a. Photomicrograph of thin (10μm) section of the Andura meteorite, an olivine bronzite-chondrite (H6). Note the strong contrast between the relatively coarse, equigranular, “metamorphic” texture of the matrix surrounding the chondrule, lower left, and the fine-grained, unrecrystallized texture of the chondrule itself and other parts of the matrix, a contrast that indicates a nonmetamorphic origin. Silicates, mostly olivine and pyroxene, show light pastel colors, metal (NiFe) brown, troilite (FeS) dark brown. This section also illustrates the extreme difficulties in performing a modal analysis optically. Length of section 2.3 mm. b. Photomicrograph of thin (10μm) section of the Pulsora olivine-bronzite chondrite (H3 to H7?). Upper left part consists of skeletal and zoned olivine (Fa_13 to Fa_16) in silica-rich glass (H3). The normal matrix, lower right, containing numerous chondrules and fragments, is unsorted, mostly fine-grained and has the same (and constant) olivine-pyroxene composition as the chondrules. Some lithic fragments, also with constant olivine composition, show an “achondritic” (H7?) texture. Silicate minerals show varying pastel colors, the glass is pinkish, and the opaques (metal and troilite) are dark. Note the eutectic metal/troilite spherule, top left. This section clearly demonstrates that the Pulsora chondrite never suffered thermal metamorphism. Length of section 3.6 mm. (Fredriksson et al., “The Pulsora Anomaly.”)

SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES • NUMBER 14

Mineral Sciences Investigations 1972–1973

George S. Switzer

EDITOR

ABSTRACT

Switzer, George S., editor. Mineral Sciences Investigations, 1972–1973. Smithsonian Contributions to the Earth Sciences, number 14, 88 pages, 29 figures, and frontispiece, 1975.—Thirteen short contributions from the Smithsonian’s Department of Mineral Sciences for 1972 and 1973 are gathered together in this volume. Scientific contributions include new data on some mercury minerals from Terlingua, Texas; a description of dashkesanite from St. Paul’s Rocks; a note on high-alumina basalt from the Aleutian Trench; descriptions of samples from the Apollo 15 and 16 lunar missions; chondrule composition of the Allende meteorite; the Pulsora meteorite and metamorphic equilibration in chondrites; the possible survival of very large meteorites that encounter the earth’s surface; data on eight observed-fall chondritic meteorites; chemical analyses of two micro-probe standards; and a technological note on the preparation of multiple micro-probe samples. A history of mineral sciences in the Smithsonian Institution and a list of meteorites in the Smithsonian collections complete the volume.

OFFICIAL PUBLICATION DATE is handstamped in a limited number of initial copies and is recorded in the Institution’s annual report, Smithsonian Year. SI PRESS NUMBER 5138. SERIES COVER DESIGN: Aerial view of Ulawun Volcano, New Britain.

Library of Congress Cataloging in Publication Data

Switzer, George S., comp.

Mineral sciences investigations, 1972–1973.

(Smithsonian contributions to the earth sciences, no. 14)

Supt. of Docs. no.: SI 1.26: 14

“Thirteen short contributions from the Smithsonian’s Department of Mineral Sciences.”

1. Meteorites. 2. Mineralogy. 3. Lunar petrology. I. National Museum of Natural History. Dept. of Mineral Sciences. II. Title. III. Series: Smithsonian Institution. Smithsonian contributions to the earth sciences, no. 14.

QE1.S227 no. 14 [QE395] 550’.8s [549] 74–10590

For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 - Price $2.50 (paper cover)

Contents

HISTORY

MINERAL SCIENCES IN THE SMITHSONIAN INSTITUTION, by Brian Mason

MINERALOGY

NEW DATA ON SOME MERCURY MINERALS FROM TERLINGUA, TEXAS, by Roland C. Rouse

DASHKESANITE: HIGH-CHLORINE AMPHIBOLE FROM ST. PAUL’S ROCKS, EQUATORIAL ATLANTIC, AND TRANSCAUCASIA, U.S.S.R., by Sara S. Jacobson

PETROLOGY

NOTE ON HIGH-ALUMINA BASALT DREDGED NEAR THE ALEUTIAN TRENCH, by William G. Melson

LUNAR STUDIES

COMPOSITION OF THREE GLASS PHASES IN AN APOLLO 15 BASALT FRAGMENT, by George S. Switzer

PETROGRAPHIC ANALYSIS OF APOLLO 16 SAMPLES 66083,1 AND 67943,1, by Brian Mason

METEORITES

THE ALLENDE METEORITE: CHONDRULE COMPOSITION AND THE EARLY HISTORY OF THE SOLAR SYSTEM, by Andrew L. Graham

THE PULSORA ANOMALY: A CASE AGAINST METAMORPHIC EQUILIBRATION IN CHONDRITES, by Kurt Fredriksson, Ananda Dube, Eugene Jarosewich, Joseph A. Nelen, and Albert F. Noonan

IMPACT SURVIVAL CONDITIONS FOR VERY LARGE METEORITES, WITH SPECIAL REFERENCE TO THE LEGENDARY CHINGUETTI METEORITE, by Robert F. Fudali and Dean R. Chapman

PRELIMINARY DATA ON EIGHT OBSERVED-FALL CHONDRITIC METEORITES, by Roy S. Clarke, Jr., Eugene Jarosewich, and Albert F. Noonan

LIST OF METEORITES IN THE NATIONAL MUSEUM OF NATURAL HISTORY, SMITHSONIAN INSTITUTION, compiled by Brian Mason

STANDARDS FOR CHEMICAL ANALYSIS

CHEMICAL ANALYSES OF TWO MICROPROBE STANDARDS, by Eugene Jarosewich

POLISHED SECTION TECHNIQUES

PREPARATION OF MULTIPLE MICROPROBE SAMPLES, by Grover C. More-land and Richard Johnson

MINERAL SCIENCES INVESTIGATIONS 1972–1973

Dedicated to

EDWARD P. HENDERSON

Curator Emeritus, Department of Mineral Sciences Smithsonian Institution

Mineral Sciences Investigations 1972–1973

Mineral Sciences in the Smithsonian Institution

Brian Mason

ABSTRACT

The Smithsonian Institution’s interest in mineral sciences extends back to the founding of the Institution, whose founder, James Smithson, published a number of mineralogical papers. This account traces the development of the mineral sciences (including all of geology, except paleontology and stratigraphy) in the Smithsonian from its founding in 1846 to 1963.

Brian Mason, Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20560.

Introduction

This history has been compiled to record the origin and development of mineral sciences as a part of the Smithsonian Institution. Mineral sciences are interpreted in a very broad sense as including all of geology, except paleontology and stratigraphy. This is essentially how the subject has evolved in the Institution, and the present Department of Mineral Sciences is responsible not only for mineralogy and petrology (both terrestrial and extraterrestrial—meteorites and lunar rocks), but also for most aspects of physical geology, including the exhibition hall “Our Restless Planet” and the answering of many queries from the public on general geology. The sources of this history include published information from annual reports and research papers, excerpts from manuscripts in the department’s files (including a lengthy historical account written by Dr. G. P. Merrill near the end of his long curatorship), and verbal reminiscences by staff members and others. The account has been carried up to 1963, when the Department of Geology was divided into two departments, Paleobiology and Mineral Sciences. This seems to be a convenient point in time to stop, since subsequent developments are well known both from published reports and from the personal knowledge of the present staff.

Although the Department of Mineral Sciences was established as recently as 1963, the Smithsonian’s interest in this field extends back to the establishment of the Institution—or even before, if we consider James Smithson’s own contributions to mineralogy. He published a number of mineralogical papers, the most notable being one in the Philosophical Transactions of the Royal Society (1803), in which he showed that the material then known as calamine comprised two distinct minerals, zinc carbonate (now known as smithsonite) and zinc silicate (hemimorphite). Along with Smithson’s monetary bequest, the Institution received his cabinet of minerals, described (Goode, 1897:305) as “a cabinet, which … proves to consist of a choice and beautiful collection of minerals, comprising probably eight or ten thousand specimens. The specimens, though generally small, are extremely perfect, and constitute a very complete geological and mineralogical series, embracing the finest vari-ties of crystallization, rendered more valuable by accompanying figures and descriptions by Mr. Smithson, and in his own writing. The cabinet also contains a valuable suite of meteoric stones, which appear to be suites of most of the important meteorites which have fallen in Europe during several centuries.” This collection was unfortunately lost in the disastrous fire at the Institution in 1865.

The original charter of the Smithsonian Institution provided not only for a museum, but also for a chemical laboratory. The chemical laboratory was established by 1853, since in his report for 1854 the then Secretary, Joseph Henry (1854:18), recorded: “The laboratory of the Institution during the past year has been used by Professor J. Lawrence Smith in the examination of American minerals. … He also made a series of analyses of meteorites, among which were fourteen specimens belonging to the cabinet of James Smithson.” This work was published as “Re-examination of American Minerals” (1853–1854) and “Memoir on Meteorites” (1855). Unfortunately, the specific meteorites from the Smithson collection are not identified and presumably were lost in the 1865 fire. J. Lawrence Smith moved to Louisville in the fall of 1854, after giving a series of lectures during the winter of 1853–1854 (for which he was paid $550, according to the financial records). Apparently, however, he worked in the Smithsonian chemical laboratory during several subsequent summers.

After the brilliant beginning provided by Smith, the mineral sciences languished for the next quarter century. Joseph Henry was unwilling to commit the Institution’s limited income for the development of a museum. Indeed, he appears to have discouraged the accumulation of large collections. In 1861 Professor Thomas Egleston of the School of Mines at Columbia University, a prominent mineralogist, was employed in the Smithsonian laboratory examining and classifying the collections representing the acquisitions of the various land office surveys, exploring expeditions, and other sources (Henry, 1862:38). It is further recorded (Henry, 1873:51) that during the interval 1861–72 “a large number of specimens in mineralogy and geology were also packed up and transmitted to Professors Egleston and Newberry of the School of Mines of New York under the existing arrangements with those gentlemen to select and label a perfect single series for the U.S. National Museum and to exchange the duplicate specimens in its interest.” This may not have been altogether in the interest of the Smithsonian Institution; Merrill comments:

It is impossible, however, from the available records to state the full number in the collections at any one time, owing to the manner in which sets were made up to send out under the administration of Messrs. Egleston and Newberry. There is here shown a singular and inexplicable discrepancy between manifested intentions and actual accomplishment since under the administration of Egleston and Newberry these collections were largely, and in some cases almost completely dissipated or depleted.

In this connection the following excerpt (Merrill, c.1925) of a letter from W. P. Blake to G. P. Merrill dated 12 October 1899 is significant:

I was also astonished in looking through the museum collection at Columbia College, New York to see the series of very remarkable concretions I collected on the Colorado desert in the cases. Wondering how they got there I inquired of Prof. Baird and he told me that an arrangement had been made with Newberry to look over the mass of material which had been accumulated with permission to him to take such duplicate material as he liked. [Merrill (c.1925) comments:] “Evidently Prof. N. made the most of his opportunity!”

In 1873 F. M. Endlich was appointed chemist and mineralogist in the Institution and served until 1879 when he resigned. During this period he was engaged during the summers as a geologist on the Hayden surveys in Colorado. Endlich reported in 1873 that the geological collections all told constituted 6300 specimens of which 3000 were minerals, representing 230 species; 2300 rocks and 500 ore specimens, with about 800 samples on hand awaiting classification. In his final report Endlich (1880: 333–335) listed 343 species and varieties of minerals in the collection.

The museum operations of the Smithsonian Institution were reorganized and greatly expanded in 1880, following the great accretion of collections from the Centennial Exhibition of 1876 and the provision of a large new building to house them (the present Arts and Industries Building). In a handwritten manuscript Merrill commented:

It was a square squatty affair of red, blue and yellow brick, exteriorly an architectural horror, interiorly a barren waste. It presented but one redeeming feature—space; and as it was space that Baird was after I presume it may at first thought have been considered a success. One can here but be reminded of the reply made by a high official after being shown thru the then newly finished Pension Office building. “Well,” it was asked, “have you any criticism?” “Yes,” was the reply, “it is fireproof.”

FIGURE 1.—George P. Merrill (1854–1929).

The expansion and reorganization of 1880 found expression in the creation of several departments and the appointment of salaried officials to take charge of the various collections. Dr. George W. Hawes was appointed curator of geology and mineralogy. In 1881 he was given three aids: F. P. Dewey for chemistry and metallurgy, G. P. Merrill for petrology (Figure 1), and W. S. Yeates for mineralogy. The organization thus formed was shortlived, being terminated by the death of Dr. Hawes on 22 June 1882. Upon the death of Dr. Hawes, Mr. Dewey was appointed an assistant curator and shortly afterwards full curator of a separate Department of Metallurgy and Economic Geology. In December 1883, Dr. F. W. Clarke of the U.S. Geological Survey was made honorary curator of the Department of Mineralogy, with Mr. Yeates as assistant. In the same year Dr. Merrill was made assistant acting curator in charge of the newly created Department of Lithology and Physical Geology. In 1889, after the resignation of Mr. Dewey to become assayer at the Bureau of the Mint, the two departments of Metallurgy and Economic Geology, and Lithology and Physical Geology were united under the title of Department of Geology, Systematic and Applied, and Dr. Merrill appointed curator. A complete reorganization in 1897 created a single Department of Geology, with three divisions: Physical and Chemical Geology, Mineralogy, and Stratigraphic Paleontology. Merrill was appointed head curator of the department, and was also curator of physical and chemical geology. Clarke remained as honorary curator of mineralogy, with Wirt Tassin assistant curator and Dr. L. T. Chamberlain as honorary custodian of gems and precious stones. The Department of Geology so constituted survived with minor modifications for over sixty years, until the creation of separate departments of Mineral Sciences and Paleobiology in

FIGURE 2.—William F. Foshag (1894–1956).

1963. Throughout this time, however, the divisions of Physical and Chemical Geology, and of Mineralogy actually functioned essentially as a single unit, although they appear as separate units on the table of organization until 1942. Merrill was effectively curator of both divisions until his death in 1929. He was succeeded as head curator of the Department of Geology by Dr. R. S. Bassler, a paleontologist, and Dr. W. F. Foshag (Figure 2) was appointed curator of both divisions. Dr. Bassler retired in 1948, and Foshag succeeded him as head curator, a position he held until his death in 1956. Dr. G. A. Cooper, also a paleontologist, then became head curator, and Dr. G. S. Switzer, curator of mineralogy, an arrangement that continued until the eventual formation of separate departments of Paleobiology and Mineral Sciences.

Functions of the Department

With this introduction, it is convenient to describe the operations of the different segments of the department under the headings of mineralogy, petrology, meteorites, and gems and precious stones.

MINERALOGY

William S. Yeates, the first appointee specifically in mineralogy, graduated M.A. in 1881 from Emory and Henry College, Virginia, and immediately thereafter became an assistant to Dr. Hawes. After Hawes’ death in 1882, Yeates remained as the salaried officer in charge of the mineral collections until May 1893, when he resigned to become state geologist of Georgia. He was apparently more an administrative officer than a scientific investigator, and his work at the Smithsonian Institution contributed little to the published record. Yeates was succeeded for a short period by O. C. Farrington, whose career is essentially linked with the Field Museum of Natural History in Chicago, where he was curator of geology from 1894 to 1930. In 1894 Wirt Tassin became assistant curator, with F. W. Clarke continuing as honorary curator.

Tassin worked in the Division of Mineralogy from 1894 to May 1909, when he resigned to go into private business. He left an interesting and informative manuscript account of the history of the division up to 1906:

FIGURE 3.—Joseph E. Pouge (1887–1971).

In 1883 Mr. F. W. Clarke was appointed honorary curator. This marks the real beginning of the present Division of Mineralogy. To Mr. Clarke more than any other is due the present standing of the collection. His appreciation of good minerals, his knowledge of their value, his enthusiasm, his widespread acquaintance and his position on the Geological Survey and on exposition boards has been of incalculable value to the collection. In fact it would be almost impossible to say too much concerning the value of his influence in securing fine specimens.

Tassin gave an account of the growth of the mineral collections from 1859 to 1906. The total number grew slowly from 793 in 1859 to 3551 in 1880, and then increased rapidly, evidently due to the reorganization, reaching 45,291 in 1895; growth then leveled off, the total in 1906 being 48,987. While Tassin evidently devoted much of his work to his curatorial and exhibition responsibilities, he also did some research. His name is associated with Dr. Merrill’s in the investigation of several meteorites, the first such research in the Institution since that of J. Lawrence Smith half a century earlier.

Tassin was succeeded in 1909 by Dr. Joseph E. Pogue (Figure 3), of whom Merrill (c.1925) remarked: “For the first time in the history of the Department the collections were administered by a

FIGURE 4. Edgar T. Wherry (1885–). Photograph taken in his garden in Chevy Chase, D. C, about 1917.

trained mineralogist.” Pogue worked as assistant curator of the Division of Mineralogy until October 1913, when he resigned to join the U.S. Geological Survey. Much of his time must have been occupied in moving the collections and exhibits into the present Natural History Building, which was opened in 1910. During his term in office Dr. Pogue visited many European museums, studying collections and displays. He also published several papers involving original research, among them a monograph on turquoise published by the National Academy of Sciences in 1915.

Pogue was followed by Dr. Edgar T. Wherry (Figure 4), who carried on the work of the division along the lines laid down by his predecessors, but who was able to devote more time to research. He published a number of papers, including one in 1917 giving the name “merrillite” to a new calcium phosphate mineral that Dr. Merrill had recognized as a meteoritic constituent in 1915. He was one of the founders of the American Mineralogist and its first managing editor (1916–1921), and president of the Mineralogical Society of America in 1923. He resigned from the Smithsonian Institution in August 1917 to join the Bureau of Chemistry of the Department of Agriculture.

When contacted in April 1972, Dr. Wherry was kind enough to provide the following reminiscences:

In 1913 I was teaching mineralogy at Lehigh University, Bethlehem, Pennsylvania, and spending summers as field assistant to Professor Florence Bascom of Bryn Mawr College in the preparation of geologic folios of quadrangles in southeastern Pennsylvania, for the U. S. Geological Survey. I was also collecting the minerals of the state, and writing articles about them. Finding these activities somewhat overtaxing I was glad to accept an invitation from Dr. George P. Merrill, head curator of Geology at the Smithsonian, to join his staff as assistant curator of Mineralogy and Petrology.

Some years before this position had been held by a Mr. Wirt Tassin, who had arranged the mineral collection as a sort of textbook, accompanying each specimen with an elaborate descriptive label, the study of which would take far more time than most visitors could spare. When he retired, his place was taken by Joseph Pogue, who rearranged the collection in accordance with standard classifications, replacing the textual labels with simple ones bearing name, composition, and locality. He resigned to go into business, and I was taken on to complete his reorganization of the collection.

My duties included answering correspondence about minerals, including especially requests for identification of specimens submitted, usually with reference to their potential commercial value. Sometimes my reports would be questioned, but to make me feel at ease, the Smithsonian office showed me a bit of pertinent correspondence: this comprised a report on a specimen made by Dr. Merrill, a response from the sender questioning its correctness, and the marginal annotation addressed by Merrill to the Secretary of the Smithsonian Institution, “If what this man says is true, Merrill ought to be fired.”

The most worth-while specimen I received was a bit of clay, and instead of an inquiry as to its value, the question was: “Is this of igneous or sedimentary origin?” Finding it to be free from quartz grains, which make up the large bulk of ordinary sediments, I guessed that it represented altered volcanic ash. I was promptly contacted by a patent-lawyer, who explained that his client held a patent on the use of igneous material for water-softening, and wished to claim royalties from the organization marketing this clay for that purpose, if it was indeed of igneous origin. I was accordingly invited to go to South Dakota where the material occurred, and study it fully. I was thereby enabled to establish the nature of “bentonite” as representing altered volcanic ash, which has had important geological applications.

In the course of that trip I stopped off at several notable mineral localities, and collected multiple specimens of such things as geodes, and lead-zinc ore-minerals. These were packed in barrels, which could then be shipped under government frank, and sent back for adding to the educational collections which the Smithsonian Institution was distributing to schools.

In those days the whole field of mineralogy was handled by one man, and I never had a technical assistant or understudy. Records were kept by a pleasantly efficient secretary, Miss Margaret W. Moody. She had scratched with a diamond point a catalog number on the back of every gem-stone; and when I resigned, it was her duty to check the gems against the catalog, to see that I had not lost any of them. It was pleasant to hear that only one ruby appeared to be missing, but that turned out to have been transferred to a special exhibit of North Carolina specimens.

Dr. Wherry was succeeded as assistant curator by William F. Foshag, and at about the same time Earl V. Shannon was appointed assistant curator in the Division of Physical and Chemical Geology, Merrill being curator of that division as well as head curator of the Department of Geology. Shannon was an accomplished analyst and a keen mineralogist, and an extremely diligent worker. Between 1919 and 1929 he published over 80 papers, many of them short notes but also some lengthy ones, including a 483-page monograph on the minerals of Idaho. Tragically he suffered a mental breakdown in 1929 and left the Institution. He was succeeded by Edward P. Henderson, who served for over 35 years until his retirement in 1966, and is still active in the department as a research associate.

In 1926 the mineral collection was enormously enriched by two remarkable bequests, which raised it from comparatively undistinguished stature to one of the world’s great mineral collections. These were the Roebling and Canfield bequests.

Colonel Washington A. Roebling (the Colonel was a Civil War veteran) was a civil engineer and the builder of the Brooklyn Bridge. During the latter work he suffered “cassion disease,” with permanent impairment of his health. This caused him to turn his attention to mineral collecting. He sought not only beautifully developed specimens but also those that were rare—indeed his aim was to secure a representative of every known mineral, however insignificant and uninteresting in appearance. In this he was eminently successful, the collection on his death lacking only about a dozen of the accepted mineral species at that time. His impaired health made travel and field collecting impossible for him, but he had ample financial means, and corresponded vigorously with mineralogists and mineral dealers throughout the world. He died on 28 July 1926, leaving his collection of 16,000 carefully selected specimens to the Smithsonian Institution. His son, John A. Roebling, generously established an endowment fund of $150,000, the income to be used for the acquisition of additional material. This endowment has provided for the continued growth of the Roebling collection.

The Canfield collection really comprises three collections. The nucleus was formed by Mahlon Dickerson of Dover, New Jersey, who began collecting in the early part of the nineteenth century. This collection passed to his nephew, Frederick Canfield, and to it were added many fine specimens collected at Franklin and Sterling Hill between 1840 and 1866. This collection, comprising some 1600 specimens, was displayed in the family mansion near Dover, where it remained until it was transferred to Washington in 1926. Frederick A. Canfield, son of Frederick Canfield, who inherited the collection, preferred to leave it intact and begin a new one of his own. This, at the time of his death on 3 July 1926, totaled some 7500 specimens. Frederick A. Canfield was educated as a geologist and mining engineer at Rutgers and Columbia Universities. In the practice of his profession he had the opportunity to travel and acquire many fine specimens at first hand. He also subsidized workmen in the railway tunnels and quarries of northern New Jersey, and in that way obtained many choice specimens of the trap rock minerals. His professional connection with the Franklin and Sterling Hill mines enabled him to keep pace with the new and rare minerals constantly found there. He also obtained many fine suites of specimens from outstanding mineral localities. With the bequest of the mineral collections Mr. Canfield also provided an endowment of $50,000 for future accessions.

Dr. Merrill died on 15 August 1929 and was succeeded as head curator of the Department of Geology by Dr. R. S. Bassler. Dr. Foshag was appointed curator of both the Division of Mineralogy and Petrology, and the Division of Physical and Chemical Geology, in effect combining the two divisions, although on the table of organization the Division of Physical and Chemical Geology survived until 1942. Dr. Foshag was born on Long Island in 1894, but his family moved to California and he graduated from the University of California in 1919. In 1917 and 1918 he served as chemist for the Riverside Portland Cement Company at the famous mineral locality of Crestmore, which probably effectively started his career in mineralogy. During his service with the Smithsonian Institution he examined many famous mineral localities in the United States and Mexico. During World War II he spent most of his time in the latter country in cooperative work with the Mexican authorities in the development of mineral deposits. During that time, in 1944, the new volcano Paricutin erupted, and he began a long-continued study of its eruptive processes and products, a study terminated by his death. His Mexican work also led him to an interest in Latin American archeology and specifically a study of jade objects from Central America. He was successful in pinpointing a source for this jade in

Guatemala. His contributions to mineralogy were recognized by the ward of the Roebling Medal of the Mineralogical Society of America in 1953.

Dr. Foshag died on 21 May 1956 and was succeeded as curator of the Division of Mineralogy and Petrology by Dr. George S. Switzer, who had joined the museum as associate curator in the division in April 1948. In August 1957 Paul E. De-sautels was appointed associate curator in the division, and later in the same year Roy S. Clarke, Jr., was appointed chemist. These men, together with Dr. Henderson and Dr. Switzer, comprised the professional staff when the division was reformed as the Department of Mineral Sciences in 1963.

PETROLOGY

Systematic petrology in the Smithsonian Institution can be fairly dated from the appointment of G. W. Hawes as curator of the Department of Geology on 1 January 1881. Hawes was one of the pioneers in the use of the petrographic microscope in the United States, having learned its use during graduate work at Yale University with Professor E. S. Dana, and at the University of Heidelberg with Professor Harry Rosenbusch; he received the Ph.D. degree from the latter university in 1880. At the same time as his appointment to the Smithsonian Institution, Hawes began an investigation of the building-stones of the United States as part of the Tenth Census; the Annual Report for 1881 (Baird, 1882:110) states:

Dr. Hawes … has gathered specimens of stone from every quarry in the United States; and a force of fifteen men, in part detailed from the Census Office, has been occupied all the year in preparing them for study and exhibition…. Numerous analyses of building-stones by the chemical and specific gravity methods have been made by Messrs. F. P. Dewey and F. W. Taylor. Since the 1st of June (1881), Mr. Geo. P. Merrill has prepared 1550 microscopic slides of building-stones, to be used in connection with the investigation.

Unfortunately Hawes developed tuberculosis during 1881, and the disease advanced rapidly. In 1882 he went to Colorado in the hope of checking it, but he died in Manitou Springs on 22 June 1882. On his death the petrographic work on the building-stones fell to G. P. Merrill, who noted in his manuscript (c.1925) that he was wholly inexperienced in this field. He evidently learned quickly and well, however, since he was one o£ the co-authors of “Reports on the Building-Stones of the United States and Statistics of the Quarry Industry for 1880” (1884), in which he contributed an article on the microscopic structure of the building-stones and eighteen reproductions of photomicrographs.

Merrill continued his petrographic work on building-stones and became an authority on the subject, writing several monographs and books thereon. He served as a special agent in this field for the Twelfth Census (1912). He was consulted frequently by both private and public officials regarding the stone to be used for various structures. He thus served in an advisory capacity in the selection of stone for the Natural History Building, the Old Post Office Building, Constitution Hall, the columns on the west face of the Treasury Building, and numerous others. Perhaps the most momentous question left for his decision was the choice of stone for the Lincoln Memorial (Yule marble from Colorado). Probably through his work on building-stones, Merrill became very interested in rock weathering, and wrote extensively on this subject, culminating in his book, A Treatise on Rocks, Rock Weathering, and Soils. He also authored The Nonmetallic Minerals: Their Occurrence and Uses.

After the turn of the century, Merrill’s interest turned to meteorites, and for the remainder of his life his research work was concentrated in this field. The petrological collections continued to grow, largely through accessions of material from the U. S. Geological Survey illustrating regional monographs and bulletins. In 1916, however, Joseph P. Iddings was appointed honorary curator of petrology, and after his death in 1920 Whitman Cross succeeded to this honorary position and held it until his death in 1949. These appointments brought two of the authors of the CIPW system of igneous rock classification into the Smithsonian Institution; a third, Henry S. Washington, was at the Geophysical Laboratory of the Carnegie Institution of Washington and many of his collections were eventually given to the Smithsonian Institution. During his period as honorary curator, Cross developed a collection of some 2000 igneous rocks comprising most of the types established by the CIPW system. Each rock has a thin section accompanying it, with a meticulous description on a file card; many are chemically analyzed. This is probably the most comprehensive systematic collection of igneous rocks in existence.

After the death of Cross active curatorial and research work in petrology was largely discontinued, because of inadequate staffing. This situation was remedied by the establishment of a Division of Petrology within the newly organized Department of Mineral Sciences in 1963, and the appointment of Dr. William G. Melson in 1964 to direct it.

METEORITES

As mentioned earlier, the original Smithson bequest included his cabinet of minerals, which contained “a valuable suite of meteoric stones, which appear to be suites of most of the important meteorites which have fallen in Europe during several centuries” (Goode, 1897:305). Some of these were analyzed by J. Lawrence Smith in the chemical laboratory of the Institution in 1853–54. Unfortunately, these meteorites were evidently lost along with the rest of Smithson’s cabinet in the fire of 1865.

The number of falls actually represented in the collection at the first date mentioned (1880) cannot with absolute certainty be given owing to the imperfection of the record, but it was small; seven localities were represented: Imilac and Vaca Muerta, Chile; Marietta (New Concord), Ohio; Parnallee, India; Searsmont, Maine; and Cold Bokkeveld, South Africa. The Tucson iron which should have formed the chief attraction was not catalogued, though brought, through the influence of Dr. B. J. D. Irwin, to Washington in 1863. The Casas Grandes iron which came to Washington from the Philadelphia Centennial should also have received attention (Merrill, c.1925).

The collection grew rapidly, evidently largely through the work of Dr. F. W. Clarke, who was appointed honorary curator in the Department of Mineralogy in December 1883. In 1889 he published a catalog of the meteorite collection as of October 1888, in which he lists 128 distinct falls and finds; in addition, there were 217 meteorites in the Shepard collection, which was deposited in the museum by Shepard’s son in 1886 (and ultimately bequeathed to the Smithsonian Institution in 1915). There was considerable duplication between the two collections and many of the specimens in both collections were fragments. Nevertheless, the building-up of the meteorite collection by Clarke, almost entirely by exchanges, was a notable contribution at this early time.

In 1888 Merrill published his first paper on meteorites, and was an active researcher in the field until his death in 1929, publishing over eighty papers on meteorites. The collection continued to grow. In 1902, Tassin brought the Clarke catalog up to date. For the purposes of this catalog the Shepard meteorites were listed along with the museum’s collection. The combined collections contained 348 distinct falls and finds. In 1916 Merrill published a “Handbook and Descriptive Catalogue of Meteorite Collections in the United States National Museum”. The combined collections at that time contained 412 independent falls and finds. The meteorite collection has continued to grow steadily and may now be the world’s largest and most comprehensive from the standpoint of the number of meteorites represented.

The tradition of meteorite research begun by Merrill has continued. Dr. Foshag wrote a number of papers on meteorites during his curatorship, and his presidential address (1940) to the Mineralogical Society of America was entitled “Problems in the Study of Meteorites.” Meteorite research within the Institution, however, became the major interest of Dr. Edward P. Henderson. Beginning in 1934 and continuing throughout his curatorship and after his retirement, he had published over thirty papers on meteorites. Many of these were written in collaboration with Stuart H. Perry (1874–1957), a Michigan newspaper publisher. Perry graduated in 1894 from the University of Michigan, where he studied chemistry, geology, and zoology. Fossils were his first love, but around 1930 his scientific interests became directed towards the study of meteorites. He was a vigorous collector, being aided in this respect by adequate private means. In 1944, the Smithsonian published Perry’s “Metallography of Mete-oritic Iron,” which for many years has been the standard reference in this field. He also compiled and privately published nine albums of photomicrographs of iron meteorites (166 in all), of which six sets were produced. Through the years that Perry was studying and collecting meteorites he generously shared his knowledge and specimens with others. Although he presented specimens to many institutions, and privately assisted others in their studies of meteorites, he was sincerely interested in the growth of the national collection and presented what he considered to be his most important specimens to the Smithsonian Institution. During his life Perry donated 192 meteorites in this way.

After J. Lawrence Smith’s death in 1883, his widow endowed the Lawrence Smith Medal, to be awarded by the National Academy of Sciences for “original investigation of meteoric bodies.” This medal was awarded to George P. Merrill in 1922, Stuart H. Perry in 1945, and Edward P. Henderson in 1970.

GEMS AND PRECIOUS STONES

This collection owes its beginning to an exhibit made by F. W. Clarke and paid for ($2500) by funds appropriated for the New Orleans Exposition of 1884. The same collection was displayed at the Cincinnati Exposition the following year, after which it was returned to Washington and placed on exhibition in the museum. A detailed description of this collection was published by G. F. Kunz in 1889. In 1891 the collection was greatly augmented by purchases from the estate of Dr. Joseph Leidy of Philadelphia, and was exhibited at the Columbian Exposition in Chicago in 1893. In 1894, Mrs. Frances Lea Chamberlain gave the museum a collection of precious stones that had been made by her father, Dr. Isaac Lea. Later, in 1897, her husband, Dr. L. T. Chamberlain, was appointed honorary curator of the collection and added a large number of desirable specimens. On his death in 1913 he bequeathed a sum of money, the income from which is used for its further increase.

The growth of the gem collection is documented by the 1900 “Descriptive Catalogue” by Wirt Tassin and in the 1922 “Handbook and Descriptive Catalogue” by G. P. Merrill. A recent popular account is Gems in the Smithsonian by Paul E. Desautels.

Literature Cited

Baird, S. F.

1882. Report of the Secretary. Annual Report of the Board of Regents of the Smithsonian Institution for the Year 1881, 839 pages.

Clarke, F. W.

1889. The Meteorite Collection in the U.S. National Museum: A Catalogue of Meteorites Represented November 1, 1886. Annual Report of the Smithsonian Institution for 1886, 2:255–265.

Desautels, P. E.

1972. Gems in the Smithsonian. Washington, D.C.: Smithsonian Institution Press.

Endlich, F. M.

1874. Mineralogical Collection. Annual Report of the Board of Regents of the Smithsonian Institution for the Year 1873, pages 51–53.

1880. List of Species and Varieties of Minerals in the National Museum of the United States in 1879. Proceedings of the United, States National Museum, 3:333–335.

Goode, G. B.

1897. The Smithsonian Institution, 1846–1896. Washington, D.C.

Henry, J.

1854. Report of the Secretary. Ninth Annual Report of the Board of Regents of the Smithsonian Institution, 463 pages.

1862. Report of the Secretary. Annual Report of the Board of Regents of the Smithsonian Institution for the Year 1861, 463 pages.

1873. Report of the Secretary. Annual Report of the Board of Regents of the Smithsonian Institution for the Year 1872, 456 pages.

Kunz, G. F.

1889. Gem Collection of the U.S. National Museum. Annual Report of the Smithsonian Institution for 1886, 2:267–275.

Merrill, George P.

1879. A Treatise on Rocks, Rock Weathering, and Soils. 1st edition, 411 pages. New York: MacMillian and Co. [2nd edition, 400 pages, published in 1906.]

1884. Reports on the Building-Stones of the United States and Statistics of the Quarry Industry for 1880. U.S. Tenth Census, 10:1–410.

1888. On the San Emigdio Meteorite. Proceedings of the United States National Museum, 11:161–167.

1904. The Nonmetallic Minerals: Their Occurrence and Uses. 414 pages. New York: John Wiley and Sons.

1916. Handbook and Descriptive Catalogue of Meteorite Collections in the United States National Museum. United States National Museum Bulletin, 94:1–206.

1922. Handbook and Descriptive Catalogue of the Collections of Gems and Precious Stones in the United States National Museum. United States National Museum Bulletin, 118:1–225.

[c. 1925.] [History of the Department of Geology.] Manuscript, files of the Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution.

Perry, S. H.

1944. Metallography of Meteoritic Iron. United States National Museum Bulletin, 184:1–206.

Pogue, J. E.

1915. The Turquoise: A Study of Its History, Mineralogy, Geology, Ethnology, Archaeology, Mythology, Folklore, and Technology. Memoirs of the National Academy of Sciences, 12 (2, 3d memoir), 162 pages, 22 plates.

Shannon, E. V.

1926. The Minerals of Idaho, United States National Museum Bulletin, 131:1–483.

Smith, J. L.

1853.–1854. Re-examination of American Minerals. American Journal of Science, 15:207–215; 16:41–53, 365–373; 18:372–381.

1855. Memoir on Meteorites. American Journal of Science, 19:153–163, 322–343.

Smithson, J.

1803. A Chemical Analysis of Some Calamines. Philosophical Transactions of the Royal Society (London), 93:12–28.

Tassin, W.

1900. Descriptive Catalogue of the Collection of Gems in the United States National Museum. Annual Report of the Smithsonian Institution for 1900, pages 473–670.

Tassin, W.

1906. [The Mineral Collections, 1859–1906.] Manuscript, files of the Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution.

Wherry, E. T.

1917. Merrillite, Meteoritic Calcium Phosphate. American Mineralogist, 2:119.

New Data on Some Mercury Minerals from Terlingua, Texas

Roland C. Rouse

ABSTRACT

An X-ray study has been performed on the three mercury minerals eglestonite, mosesite, and kleinite. Previous work is reviewed and, where necessary, corrected in the light of new data. Eglestonite is cubic, Ia3d, with a = 16.04 Å and has the formula Hg_4 Cl_2O. Mosesite and kleinite are mercury nitrogen chloride sulfates. Mosesite is cubic with a = 28.62 Å and kleinite, hexagonal with α = 40.60 and c = 11.16 Å. Although the chemical formulas of their supercells are still uncertain, their subcell formulas correspond essentially to the chloride salts of Millon’s base (Hg_2NOH · H_2O).

Roland C. Rouse, Department of Geology and Mineralogy, The University of Michigan, Ann Arbor, Michigan 48104.

Introduction

The mercury deposit at Terlingua, Brewster County, Texas, is known mineralogically for its suite of secondary mercury minerals. It is, in fact, the type locality for six of them including terlinguaite (Hg_4O_2Cl_2), eglestonite (Hg_4Cl_2O), and the mercury nitrogen chloride sulfates mosesite and kleinite. These minerals are known from but a few localities and one investigator (Lipscomb, 1957) in a review of the crystal chemistry of mercury found it quite remarkable that kleinite and mosesite should occur at all in nature. The latter two are of particular interest as they are thought to be stuffed derivatives of the high tridymite and high cristobalite structures, respectively. They contain NHg_4 tetrahedra, which play the same structural role as SiO_4 tetrahedra do in silicates.

There exists one definitive study of the whole group, that of Hillebrand and Schaller (1909). Subsequent investigators have compiled a large body of chemical, optical, and crystallographic data, but their results have often been ambiguous or contradictory. An accurate determination of the crystal structure has been made only for terlinguaite and since this has resolved most of the problems associated with this mineral, it was not included in the present study. The terlinguaite structure (Aurivillius and Folkmarson, 1968) is interesting from a crystal chemical viewpoint as it contains mercury in two valence states. Some of the mercury atoms are divalent and form the characteristic linear O-Hg-O groups (Grdenić, 1965). Others are arranged in equilateral triangular clusters in which each mercury has a formal oxidation number of + 4/3. The Hg–Hg distances in the cluster are shorter than those in solid mercury indicating in-termetallic bonding, and terlinguaite is therefore a metal cluster compound.

Experimental Methods

The study of eglestonite, mosesite, and kleinite is rendered difficult by their tendency to occur as multiple crystals, whether as twins, parallel growths or random intergrowths. In the case of kleinite this seems to be invariably the case. The specimens used in this study were from Terlingua and Huahuaxtla, Mexico, and were obtained from the U. S. National Museum collections. As reported by previous workers, eglestonite is photosensitive, its color changing rapidly from yellow to brown to black. The color change produced no obvious changes in the x-ray diffraction patterns, but this matter was not investigated systematically.

Unit cell parameters were determined from precession photographs and verified by the cone-axis or rotating crystal methods. Space groups were determined from precession and Weissenberg photographs taken with MoKα and CuKα radiations, respectively. The cell parameters were refined from powder data by the method of least-squares using the program of Appleman and Evans. In the case of mosesite and kleinite the data were obtained from a powder diffractometer utilizing monochro-matized CuKα radiation and quartz as an internal standard. Since there was not enough eglestonite available for this procedure, it was necessary to use 16 reflections between 102° and 165° 2θ measured from a Debye-Scherrer photograph. The powder patterns in Tables 1, 2, and 3 were likewise measured from shrinkage-corrected Debye-Scherrer photographs taken with a 114.6 mm diameter camera and filtered CuKα radiation. Intensities were estimated visually.

Minerals Studied

EGLESTONITE

Eglestonite was first described by Moses (1903) as a cubic mineral having the formula Hg_6Cl_3O_2. Hillebrand and Schaller (1909:145, 147) confirmed the cubic symmetry but found the formula to be Hg_4Cl_2O on the basis of three chemical analyses. The crystal class was determined to be m3m from the presence of the hexoctahedron as a common form.

The crystal structure of eglestonite is of some interest due to the presence of the binary ion Hg_2+2. Two structures have been proposed, both by the same investigator. Hedlik (1948) found eglestonite to be cubic, Pm3n, with α = 16.07 Å. She went on to propose a structure containing the mercurous ion and having Hillebrand and Schaller’s chemical formula. However, in Hedlik (1950) there appeared a revised structure based on a cell having a = 8.03 Å and symmetry Im3m. The formula was also changed to Hg_6Cl_4O, which is not in accord with the existing chemical analyses. No explanation was offered for the revisions and since both structures were derived with powder and rotating crystal data, neither can be considered reliable. To compound the confusion, Wolfe (cited in Palache, et al., 1951:51) reported the cell parameter a = 16.03 Å and a probable space group Ia3d for eglestonite.

The present study has confirmed Wolfe’s results. Eglestonite is cubic, Ia3d, with a refined parameter a = 16.0398 ± 0.0003 Å. There is also a very prominent

TABLE 1.—Powder pattern of eglestonite

I

dobs

dcalc

hkl

10

6.549

6.548

211

40

4.006

4.010

400

100

3.271

3.274

422

<1

3.142

3.146

510, 431

7

2.925

2.928

521

7

2.832

2.835

440

10

2.599

2.602

611, 532

50

2.529

2.536

620

5

2.471

2.475

541

10

2.313

2.315

444

5

2.265

2.268

543, 710, 550

<1

2.179

2.183

721, 633, 552

<1

2.135

2.143

642

1

2.034

2.037

651, 732

1

2.003

2.005

800

80

1.887

1.890

660, 822

1

1.858

1.865

831, 750, 743

<1

1.811

1.816

752

3

1.788

1.793

840

20

1.707

1.710

664

1

1.687

1.691

851, 930, 754

10

1.633

1.637

844

<1

1.617

1.620

941, 853, 770

1

1.586

1.588

10 · 1 · 1, 772

1

1.554

1.558

943

5

1.526

1.529

10 · 3 · 1, 952

5

1.499

1.502

871

<1

1.475

1.477

961, 10 · 3 · 3

5

1.461

1.464

10 · 4 · 2

1

1.384

1.386

11 · 3 · 2, 10 · 5 · 3, 972

5

1.373

1.375

10 · 6 · 0, 866

10

1.334

1.337

12 · 0 · 0, 884

<1

1.308

1.310

10 · 7 · 1, 11 · 5 · 2

<1

1.290

1.293

12.3.1, 983

5

1.266

1.268

12 · 4 · 0

3

1.237

1.237

10 · 8 · 2

<1

1.215

1.216

13 · 2 · 1, 11 · 7 · 2

5

1.182

1.182

12 · 6 · 2

Plus ca. 65 more lines to 0.777 Å

subcell having A = a/2 = 8.02 Å and symmetry Im3m. That the 16.04 Å cell is the correct one is confirmed by powder data (Table 1), which can only be indexed fully on the larger cell. The unit cell contents calculated from the average of Hille-brande’s analyses are Hg94.11 Cl49.16 O23.76. From a consideration of the available equipoints in Ia3d, the correct formula must be Hg_4Cl_2O with Z = 24. These results indicate that Hedlik’s revised structure is necessarily wrong since it is based on the subcell rather than the true cell and gives a formula inconsistent with the chemical analyses. Preliminary work on a redetermination of the eglestonite structure is underway and a complete study is planned.

MOSESITE

Mosesite was described by Canfield, et al. (1910) as a new mercury-ammonium compound containing chloride, sulfate, and water. Although cubic in morphology, it was weakly birefringent but became isotropic when heated to ~186°C. From this they concluded that mosesite exists in high and low temperature polymorphic forms with the inversion temperature being 186°C. This, of course, is not necessarily the case as many cubic materials show a weak, anomalous birefringence. In a study of mosesite from the Fitting district of Nevada, Bird (1932) found on the basis of powder data that mosesite is cubic with a face-centered lattice and α = 9.57 Å.

A restudy of mosesite was performed by Switzer, et al. (1953), who obtained the first complete chemical analysis of the mineral. Noting the strong similarity of its powder pattern and chemistry to those of Millon’s base (Hg_2NOH · 2H_2O), they derived a formula Hg_2N(Cl,SO_4,MoO_4,CO_3) · H_2O (Z=8) for material from Huahuaxtla Mexico. Mosesite is, therefore, the chloride salt of Millon’s base with lesser amounts of other large anions. The structure of Hg_2NOH · H_2O was determined by Lipscomb (1951) to be cubic, F43m, with α = 9.58 Å. It is a stuffed derivative of the high cristobalite structure with a 3-dimensional framework of linked NHg_4 tetrahedra. The OH− and H_2O occupy the large open channels in the framework. This explains the presence of large complex anions in the mosesite formula. Switzer, et al. (1953) also proposed a structure for mosesite analogous to that of Millon’s base. The structure is cubic, , with a = 9.524 Å, which is consistent with the powder pattern.

The author has reexamined the mosesite crystals from Huahuaxtla, Mexico, analyzed by Fahey (in Switzer, et al., 1953). Although the X-ray study of this material is not yet complete, several important results can be reported. Weissenberg photographs

TABLE 2.—Powder pattern of mosesite

1

dobs

dcalc

hkl

75

5.512

5.508

333, 511

10

3.375

3.373

660, 822

90

2.877

2.876

933, 771, 755

100

2.756

2.754

666, 10 · 2 · 2

40

2.382

2.385

12 · 0 · 0

40

2.186

2.188

993, 13 · 1 · 1

25

1.834

1.836
1.832

999, 15.3.3
12 · 10 · 0

35

1.685

1.686
1.683

12 · 12 · 0
17 · 0 · 0

25

1.610

1.612
1.607

17 · 5 · 1
14 · 11 · 0

20

1.454

1.455
1.453

19 · 5 · 1
18 · 8 · 0

30

1.436

20

1.375

20

1.334

20

1.241

10

1.192

10

1.165

15

1.102

20

1.093

15

1.066

15

1.047

Plus ca. 16 more lines (mostly broad bands) to 0.787 Å

confirm the cubic symmetry, but the space group has not yet been determined with certainty. A rotating crystal photograph shows that mosesite has a supercell with α = 28.8 Å, three times the value previously reported. The refined value is a = 28.618 ± 0.002 Å. The subcell has A = a/3 = 9.54 Å. There is also a second subcell, defined by the strong reflections, which has A’ = a/12 = 2.38Å.

Powder data for mosesite are presented in Table 2. The pattern is similar to that of Switzer, et al. (1953), except that the d-values and intensities of the reflections are in better agreement with those of Hg_2NOH · 2H_2O than are the data of Switzer, et al. This is especially true of the line at 5.512 Å, whose intensity is much greater than reported by those authors. The indexed reflections in Table 2 do obey the presence rule for a face-centered 9.54 Å cell. Powder diffractometer scans, however, show a small peak at 12.87 Å, which can only be indexed as 210 (dcalc= 12.80 Å) of the 28.62 Å supercell. This is in accord with the single crystal results and also seems to require a primitive lattice for mosesite. It is possible that the 9.54 Å subcell is face-centered, while the supercell is primitive. The substructure corresponds to the structure of Millon’s base and the superstructure is perhaps connected with ordering of the several kinds of large interstitial anions in mosesite. The symmetry and lattice type of the supercell is the subject of continuing single crystal studies.

KLEINITE

A fourth yellow mercury mineral occurring at Terlingua was mentioned by Moses (1903), but it remained for Sachs (1905) to name it kleinite. Hillebrand and Schaller (1909) found it to be another mercury ammonium compound with chloride and sulfate, but despite many chemical analyses they could not derive a satisfactory formula. They also described in detail the highly anomalous optical properties of kleinite. Although the mineral is morphologically hexagonal, basal sections are strongly birefringent. Above about 130°C, however, kleinite becomes uniaxial and, as in the case of mosesite, this was ascribed to polymorphism. They also noted that birefringent basal sections would not extinguish under crossed polars. This was explained by assuming each crystal to be composed of a group of parallel biaxial plates stacked along c. During further heating experiments, Canfield, et al. (1910) made the interesting observation that kleinite becomes isotropic above 186°C.

In an x-ray investigation Heritsch (1949) found that all kleinite crystals are composed of several individuals and that heating above the supposed inversion temperature does not change this. His crystals were all hexagonal, probably P6_3/mmc, with a=13.56 and c=11.13 Å. There is also a sub-periodicity of a/2 = 6.78 Å. A crystal structure was deduced using rotating crystal data. In a later paper Heritsch (1954) noted that mosesite had been shown to be isostructural with Millon’s base, which is in turn a high cristobalite derivative. By analogy, he proposed that kleinite is a high tridymite derivative with the formula (Hg_2N) (Cl,SO_4) · xH_2O where x~1/4. As with mosesite the structural channels contain the large anions and water molecules.

Nijssen and Lipscomb (1954) came to the same conclusion on the basis of the close relationship between kleinite and Hg_2NBr. They determined the structure of the latter to be a derivative of high tridymite. Hg_2NBr is hexagonal, P6_3/mmc, with a = 6.65 and c=11.26 · , which corresponds to the kleinite subcell. In a later paper, however, Lipscomb (1957) reported evidence that the a parameter of kleinite given by Heritsch should be tripled. He further suggested on the basis of some intensity calculations that the channels in the kleinite structure contain mercury atoms as well as anions.

In the present study, the interpretation of the diffraction photographs was greatly hindered by the fact that every crystal examined was multiple. In some cases, however, the volume of one individual was considerably greater than those of the others. It was therefore possible to separate its reciprocal lattice pattern from those of the others and study its symmetry and cell parameters. This approach is not infallible, but its results are supported by the powder data, which are not subject to the uncertainties introduced by the multiplicity of the single crystals.

Rotation photographs around the c-axis are consistent with Hillebrand and Schaller’s model of a stacking of parallel plates along c. Adjacent individuals, however, seem to be slightly tilted with respect to one another by ~1.5° in those crystals examined.

As suggested by Lipscomb (1957), kleinite is hexagonal with a three times the value given by Heritsch. The refined cell parameters are a = 40.599 ±0.005 and c=11.155±0.003 Å. There are two subcells. One, defined by the total pattern of medium plus strong reflections, has A= a/6 = 6.77 and C = c= 11.16 A. The other, defined by the strong reflections alone, has A’ = a/12 = 3.39 and C’’ = c/2 = 5.58 Å. An independent check on these parameters is provided by the powder pattern (Table 3). It contains four low-angle reflections (220, 222, 811, and 702), which cannot be indexed on Heritsch’s cell but which can be indexed quite satisfactorily on the 40.60 Å cell.

The space group of the supercell could not be determined since the superstructure reflections on the Weissenberg photographs are too few and scattered. However, the 6.77 Å subcell does have symmetry P6_3mc, P62c, or P6_3/mmc. This subcell is the analog of the Hg_2NBr cell.

Using the average chemical analysis of Hillebrand and Schaller (1909), the supercell contents are

Hg330.47N141.41Cl158.95S24.96O143.91H88.14

TABLE 3.—Powder pattern of kleinite

1

dobs

dcalc

hkl

10

10.19

10.15

220

15

5.871

5.860

600

15

5.577

5.577

002

25

5.188

5.188

601

5

4.890

4.888

222

20

4.040

4.040

602

<1

3.850

3.861

811

3.836

820

1

3.731

3.732

702

10

3.382

3.383

660

5

3.132

3.140

603

3.127

433

100

2.931

2.930

12 · 0 · 0

70b

2.888

2.893

662

2.890

860

2.883

752

15

2.831

2.834

12 · 0 · 1

90

2.788

2.789

004

3

2.688

2.693

903

2,689

224, 960

100

2.592

2.594

12 · 0 · 2

2.592

504

5

2.518

2.518

604

2.513

10 · 4 · 2

<1

2.446

5vb

2.306

10

2.215

10

2.171

1

2.084

10

2.057

20vb

2.019

3

1.900

15

1.843

3

1.772

3

1.736

30

1.690

Plus ca. 40 more lines (mostly broad bands) to 0.781 Å

bbroad, vbvery broad

On the basis of the available data it is difficult to derive a satisfactory formula from this. A formula for the 6.77 Å subcell, however, may be derived by analogy to that of Hg_2NBr. The subcell contents are

Hg9.18N3.93Cl4.42S0.69O4.00H2.45

or very nearly Hg_9N_4(Cl,SO_4)5 · H_2O. This can be rewritten as 4Hg_2NCl · Hg(Cl,SO_4) · H_2O. Presumably, the 4Hg_2NCl represents that part of the substructure analogous to Hg_2NBr (for which Z = 4), while the remainder represents the contents of the structural channels.

The true symmetry and formula of the superstructure can only be settled by a complete structure determination combined with a new chemical analysis. The former objective, however, may not be attainable due both to the lack of single crystals and the experimental difficulties inherent in treating highly absorbing compounds with very large supercells. The outlook for mosesite is more hopeful, however, and further work is anticipated on this mineral.

Literature Cited

Aurivillius, K., and L. Folkmarson

1968. The Crystal Structure of Terlinguaite Hg_4O_2Cl_2 · Acta Chemica Scandinavica, 22:2529–2540.

Bird, P. H.

1932. A New Occurrence and X-Ray Study of Mosesite. American Mineralogist, 17:541–550.

Canfield, F. A., W. F. Hillebrand, and W. T. Schaller

1910. Mosesite, a New Mercury Mineral from Terlingua, Texas. American Journal of Science, 4th series, 30:202–208.

Grdenić, D.

1965. The Structural Chemistry of Mercury. Quarterly Reviews (London), 19:303–328.

Hedlik, A.

1948. Über die Formel und Struktur von Eglestonit. Experientia, 4:66.

1950. Über Formel und Struktur des Mercurooxychlorides Eglestonit. Tschermaks Mineralogische und Petro-graphische Mitteilungen, Dritte Folge, 1:378–389.

Heritsch, H.

1949. Röntgenuntersuchungen an Kleinit. Tschermaks Mineralogische und Petrographische Mitteilungen, Dritte Folge, 1:300–312.

1954. Bemerkungen zur Kristallchemischen Konstitution des Kleinites. Anzeiger der Österreichischen Akademie der Wissenschaften, Mathematisch-Wissenschaftliche Klasse, 1:1–4.

Hillebrand, W. F., and W. T. Schaller

1909. The Mercury Minerals from Terlingua, Texas. United States Geological Survey Bulletin, 405.

Lipscomb, W. N.

1951. The Structure of Millon’s Base and Its Salts. Acta Crystallographica, 4:156–158.

1957. Recent Studies in the Structural Inorganic Chemistry of Mercury. Annals of the New York Academy of Sciences, 65:427–435.

Moses, A. J.

1903. Eglestonite, Terlinguaite and Montroydite, New Mercury Minerals from Terlingua, Texas. American Journal of Science, 4th series, 16:253–263.

Nijssen, L., and W. N. Lipscomb

1954. A Hexagonal Modification of a Salt of Millon’s Base. Acta Crystallographica, 7:103–106.

Palache, C, H. Berman, and C. Frondel

1951. Dana’s System of Mineralogy. Volume 2, 7th edition. New York: John Wiley and Sons.

Sachs, A.

1905. Der Kleinit, ein Hexagonales Quecksilberoxydchlorid von Terlingua in Texas. Sitzungberichte der Königlichen Preussischen Akademie der Wissenschaften (Berlin), 1091–1094.

Switzer, G., W. F. Foshag, K. J. Murata, and J. J. Fahey

1953. Re-examination of Mosesite. American Mineralogist, 38:1225–1234.

Dashkesanite: High-Chlorine Amphibole from St. Paul’s Rocks, Equatorial Atlantic, and Transcaucasia, U.S.S.R.

Sara S. Jacobson

ABSTRACT

New data are given for dashkesanite, a high-chlorine amphibole, from two localities, Transcaucasia, U.S.S.R., and St. Paul’s Rocks, Equatorial Atlantic. Four new analyses (by electron microprobe) of the mineral from Transcaucasia gave a chlorine content ranging from 4.15 to 5.34 percent. The original analysis by Krutov (1936) by wet chemical methods reported Cl = 7.24 percent. Five analyses (by micro-probe) of dashkesanite from St. Paul’s Rocks gave Cl ranging from 6.03 to 6.51 percent. The mineral from both localities is low in SiO_2 and MgO and high in FeO, Cl, and K_2O compared to other hornblende compositions. It is hastingsitic using the classification of Ernst (1968).

Sara S. Jacobson, Department of Geology, University of California, Los Angeles, Los Angeles, California 90024.

Introduction

High-chlorine amphibole was first described by Krutov (1936). He found the mineral in skarn rocks surrounding sheetlike magnetite ore bodies at Dashkesan, Transcaucasia, U.S.S.R. These skarn rocks occur about 1200 meters from the ore body and extend for over 200 meters with an average thickness of 0.60–0.75 meters. The surrounding country rock is described as porphyrites and tuffs with dikes of gabbro porphyrite occuring near the skarn. Krutov (1936) named the mineral “dashkesanite” for the locality.

The mineral was also found by Melson, et al. (1972) in brown hornblende mylonites from St. Paul’s Rocks, an ultrabasic intrusion exposed in a series of islets in the equatorial Atlantic. Brown hornblende mylonites are the second most abundant of three rock types found on the islets; peridotite mylonites are the most abundant rock type and clinopyroxene mylonites are the least abundant. All samples examined were collected in 1966 during Cruise 20 of the R. V. Atlantis II. Samples from both of these areas were investigated in the present study.

ACKNOWLEDGMENTS.—I wish to thank W. G. Melson for suggesting the project and his help throughout.

Petrography

The specimen from Transcaucasia available for study (USNM 120180) consists of fine- to mediumgrained, subhedral to anhedral crystals of dashkesanite; minor chlorite and epidote and a finegrained material that may be scapolite are also found in the specimen. This specimen of dashkesanite is dark green. In thin section, it shows a strong yellow to blue-green pleochroism. Cleavage is not well developed; rather a basal parting appears to dominate. The mineral has inclined extinction and positive elongation.

Dashkesanite from St. Paul’s Rocks was studied in two sections of brown hornblende mylonite, (USNM 110393–13 and 110393–31). Both are from the Southeast Islet. (See Melson, et al., 1972, for map of localities.) The primary assemblage is kaersutitic hornblende, plagioclase, and Fe-Ti oxides. These occur with accessory amounts of dashkesanite, allanite, zircon, scapolite and titanbiotite.

FIGURE 1.—Portion of a hornblende augen in section USNM 110393–13. The diagonal grayish area in the central part of the photo is dashkesanite. Width of field is 1.6 mm × 1.3 mm.

The hornblende forms large rounded augen. Dashkesanite occurs in veins in the augen and as overgrowths on the hornblende augen. It is also found in veins in the fine-grained matrix. It does not occur disseminated in the matrix (Figure 1).

The optical properties of the St. Paul’s Rocks dashkesanite are similar to those described for the mineral from the type locality. The dashkesanite forms fine to coarse, anhedral to subhedral masses; good crystal forms are rare. The mineral again shows the distinctive, strong yellow-green to blue-green pleochroism. The dashkesanite is not sheared nor mylonitized.

Analytical Procedure

Analyses of the above samples were done on an ARL EMX electron microprobe using a 15kV acceleration potential, 0.15 μA sample current and a

TABLE 1.—Amphibole analyses

10μm–15μm beam size. The analyses were corrected using the Bence and Albee (1968) correction procedures, and the summations corrected for chlorine equivalents of oxygen. The results are given in Table 1. The ionic proportions were calculated on the basis of 24 anions with H_2O not determined and all Fe assumed to be ferrous. The choice of 24 anions rather than 23 was made because Cl− rather than OH− appears to nearly completely fill the A site. Since the occupancy of this site is known and need not be assumed, a normalization on the basis of 24 anions is a justified approximation. The actual number of anions is probably between 23 and 24.

Chemistry

Dashkesanite from the two localities has similar chemistry in some respects. Both are low in SiO_2 and MgO and high in FeO, Cl, and K_2O compared to other hornblende compositions (Leake, 1968; Deer, et al., 1963a:290), while CaO, TiO_2, and Al_2O_3 are consistent with other hornblendes. These hornblendes are hastingsitic, using the classification of Ernst (1968).

There are also chemical differences between the two occurrences. The dashkesanite from the St. Paul’s Rocks is higher in SiO_2, Cl, Na_2O, MgO and lower in total Fe and K_2O than the dashkesanite from Transcaucasia. There are also differences between Krutov’s original analyses and those done for the present paper. The new analyses show less Cl, SiO_2, and Na_2O, and higher Al_2O_3. These differences may be due to the differences in analytical technique.

The cation sums (Table 1) are high, generally summing over 16. This is probably because for the microprobe analyses all iron is assumed to be ferrous. Krutov’s analysis shows a considerable amount of ferric iron, and indicates that from 13 to 14 percent of the ferrous iron reported in the probe analyses may be ferric.

Particularly, the totals for the Y site (Fe + Ti + Mg + octahedral Al) are high, being between 5.23 and 5.50. Leake (1968:249) postulates that good analyses would have sums between 4.75 and 5.25 for this site. Recalculating the ionic proportions assuming all iron as ferric iron reduces the sum for this site by approximately 0.70 and reduces the cation total by approximately 1. Depending on the amount of ferric iron present, all the cation proportions are probably less than those reported for the present analyses in which all iron is assumed as ferrous iron.

Discussion

Dashkesanite from the two localities is close in optical characteristics and chemical composition in spite of the differences in the environments in which they are found. In St. Paul’s Rocks dashkesanite is a late stage mineral, as shown by the absence of shearing or mylonitization. Melson, et al. (1972:241) include dashkesanite in the neomineral group. These minerals occur as undeformed grains indicating formation by recrystallization and precipitation continuously during or after mylonitization. Melson, et al. (1972:241) speculate the high-chlorine minerals found (dashkesanite, scapolite and chlorapatite) formed either by reaction of primary minerals with a chlorine-rich pore fluid or by direct crystallization from such a pore fluid.

It is possible that the chlorine was derived from sea water during weathering of the brown hornblende mylonites. The dashkesanite does occur with scapolite, however, which is most characteristically formed in upper amphibolite facies rocks (Deer, et al., 1963b:330); this would indicate moderate to high temperatures.

The formation of the dashkesanite may be related to the formation of the brown hornblende mylonites. Of the three rock types present, the brown hornblende mylonites have the largest amount of chlorine in their bulk composition (1.22–1.86% compared with 0.67% in the clinopy-roxene-plagioclase mylonite and 0.05–0.20% in the peridotite mylonites [Melson, et al., 1972]). The higher amount of chlorine may account for the observable presence of the dashkesanite and other high chlorine phases in the brown hornblende mylonites. High chlorine content appears to be a characteristic of the strongly undersaturated alkalic rock clan to which the brown hornblende mylonites are chemically related (Melson, pers. comm.).

The dashkesanite in the Trancaucasian rocks formed by contact metamorphism. Krutov (1936) feels that the dashkesanite was formed by reaction of the fluids from the magma, containing large amounts of FeO and Cl, with the surrounding country rocks described as porphyrites and tuffs. He projects conditions of low temperature and high fluid pressure. Krutov (1936) thinks the source of the fluids are the basic differentiates of the intrusion, which have a high chlorine content. These basic differentiates occur as dikes of gabbro porphyrite near the amphibole skarn.

The differences in chemistry between the two localities of dashkesanite as noted in the preceding section can be accounted for by the differences in environments. There are, however, strong similarities between the two environments. Both occurrences are in silica-undersaturated environments and this would account for the low SiO_2 content of dashkesanite. Although the specific conditions of formation are not known, both occurrences of the mineral appear to be related to the late stage fluids derived from basic and ultrabasic intrusions. Dashkesanite may be present but may not have been recognized in other rocks of similar composition as the Transcaucaian rocks and St. Paul’s Rocks. Further observance of this mineral in other silica-undersaturated rocks could add to our knowledge of the geochemistry of chlorine, the concentration of chlorine in such rocks, and the late stage fluids associated with these rocks.

Dashkesanite may also prove interesting crystal-lographically because the chlorine ion is the largest (1.81 Å) of the ions commonly reported in the A site in amphiboles (OH−, 0.91–0.105 Å and F−, 1.33 Å [Bloss, 1971]).

Literature Cited

Bence, A. E., and A. L. Albee

1968. Empirical Correction Factors for the Electron Microanalysis of Silicates and Oxides. Journal of Geology, 76:382–403.

Bloss, F. Donald

1971. Crystallography and Crystal Chemistry. 545 pages. New York: Holt, Rinehart and Winston, Inc.

Deer, W. A., R. A. Howie, and J. Zussman

1963a. Chain Silicates. Volume 2 of Rock-Forming Minerals. 379 pages. New York: John Wiley and Sons.

1963b. Framework Silicates. Volume 4 of Rock-Forming Minerals. 435 pages. New York: John Wiley and Sons.

Ernst, W. G.

1968. Amphiboles. 125 pages. New York: Springer-Verlag New York, Inc.

Krutov, G. A.

1936. Dashkessanite: A New Chlorine Amphibole of the Hastingsite Group. Bulletin de l’Academie des Sciences de l’URSS, Classe des Sciences Mathematiques et Naturelles, Serie Geologique, 341–373. [See also Mineralogical Abstracts, 6(1937): 438.]

Leake, B. E.

1968. A Catalog of Analyzed Calciferous and Subcalciferous Amphiboles Together with their Nomenclature and Associated Minerals. Geological Society of America Special Paper, 98.

Melson, W. G., S. R. Hart, and G. Thompson

1972. St. Paul’s Rocks, Equatorial Atlantic: Petrogenesis, Radiometric Ages and Implications on Sea Floor Spreading. Geological Society of America Memoir, 132:241–272.

Note on High-Alumina Basalt Dredged near the Aleutian Trench

William G. Melson

ABSTRACT

High-alumina basalt was dredged from a small seamount in the Adak Fracture Zone near and south of the Aleutian Trench. The basalt, dredged from magnetic anomaly 25 (about 63 million years old) has a composition transitional between basalt from spreading centers and basalt from seamounts. It thus may have been derived from the ancestral East Pacific Rise or from younger off-ridge volcanism. Extensive weathering effects have changed the concentrations of some elements, and obscured the primary igneous composition.

William G. Melson, Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, D. C. 20560.

Introduction

Very little is known about the igneous rocks on the floor of the north Pacific Ocean. Samples dredged from this region were transferred to the National Museum of Natural History, Smithsonian Institution, by Dr. Barrett H. Erickson of the U.S. National Oceanographic and Atmospheric Administration. These are the only samples in the Museum’s collections from this area, and their description is the subject of this report.

ACKNOWLEDGMENTS.—I am indebted to Dr. Erickson for providing the samples for study; to Mr. Paul Grim, also of the U.S. National Oceanographic and Atmospheric Administration, for helpful discussions and information on the Adak Fracture Zone; to Mr. E. Jarosewich, National Museum of Natural History, Smithsonian Institution, for performing the chemical analyses; and to Dr. S. R. Cann and his associates, University of East Anglia, England, for performing trace element analyses on the samples.

Specimen Features

Two basalt samples were received, both identical in hand specimen features and weighing 195 gm (USNM 112471) and 400 gm (USNM 112472). Both are angular, and have very thin, black, hydrous iron-manganese oxide coatings on at least one surface. Other surfaces are free of the coatings, indicating that the fragments were broken off larger boulders or outcrops by the dredge. A thin, 5 to 10 mm, reddish altered zone extends inward into the rock from the oxide-encrusted surfaces. The unencrusted surfaces are mottled by small black circular encrustations, probably composed of hydrous iron-manganese oxides, about 1 to 2 mm across, on a yellowish background of altered basalt. The less-altered appearing interior is dark brown, contains scattered large (up to 1 cm across) rounded, multicrystal aggregates of plagioclase (An_80), which compose about 3 volume percent of each sample. The groundmass contains abundant plagioclase micro-lites (average An_60-An_70), and small granules and sheaflike quench crystals of clinopyroxene. The large plagioclase crystals are altered to white clay minerals on the outer, oxide-encrusted surface. The very fine grain-size of the samples shows that they cooled near quenched surfaces, although neither fresh glass nor palagonitized glass surfaces occur. There are no obvious grain-size gradients across the samples. These features indicate that the samples are from the interior, but probably less than 20 centimeters from a cooling surface, of a pillow lava or from the contact of a shallow intrusion.

Bottom Exposure Age

The thickness of the hydrous iron-manganese oxide coating on deep-sea rocks is proportional to the length of time of exposure on the sea-floor. The rate of deposition ranges between 1 and 10 mm per million years (Bender et al., 1966; Ku and Broecker, 1967; Somayujulu, 1967). The maximum thickness of 1 mm on these samples thus indicates a bottom exposure age of from 0.1 to 1 million years.

Sample Locality and Oceanic Basement Age

The sample was dredged from a depth of 4714 m on the south side of a small seamount which rises to 3790 m. The locality (49°30.43’ N, 177°32.88’ W) is on magnetic anomaly 25 (Grim and Erickson, 1969; Erickson and Grim, 1969), which has an age estimated at 63 million years according to the magnetic reversals time scale of Heirtzler, et al. (1968). The thin hydrous iron-manganese encrustation shows that the sample has been exposed at the sea floor for a much shorter period of time than this. The inference, then, is that it has only recently been exposed at the sea-floor by faulting or slumping off of overburden, and/or it is a geologically recent eruptive rock.

The unnamed seamount from which the samples were dredged is elongated in an east-northeast direction, and rises 1210 m over a distance of 15 km in this direction. Steepest slopes are perpendicular to this direction, and average about 10°. The bathymetry itself would indicate formation of the feature as an off-ridge submarine volcano. However, the direction of elongation is nearly paralled to the trend of the regional magnetic anomalies. This feature raises the possibility that the seamount was a bathymetrically high ridge formed originally at a spreading center. The composition of the basalt from the seamount, as will be discussed, does not indicate unambiguously which of these possibilities is true.

Composition

The Adak Fracture Zone basalt samples are high-alumina basalt with evidence of significant weathering

TABLE 1.—Chemical composition of high-alumina basalt from the Adak Fracture Zone

Constituent

1

2

3

4

5

SiO_2

46.80

49.61

0.72

49.84

48.16

Al_2O_3

17.99

16.01

0.85

14.09

18.31

Fe_2O_3

7.52

2.21

0.74

3.06

4.24

FeO

3.52

7.19

1.25

8.61

5.89

MgO

4.48

7.84

0.90

8.52

4.87

CaO

12.14

11.32

0.64

10.41

8.79

Na_2O

2.84

2.76

0.25

2.15

4.05

K_2O

0.37

0.22

0.12

0.38

1.69

H_2O+

1.66

0.63

0.22

–

–

H_2O−

0.77

0.45

0.30

–

–

TiO_2

1.67

1.43

0.29

2.52

2.91

P_2O_3

0.17

0.14

0.07

0.26

0.93

MnO

0.19

0.18

0.04

0.16

0.16

Total

100.12

–

–

–

–

Total FeO*

10.05

11.49

1.27

11.36

9.71

TRACE ELEMENTS (ppm)

Rb

7.2

–

–

–

–

Sr

148

123

46

–

–

Y

57

43

12

–

–

Zr

111

100

42

–

–

Nb

0.8

–

–

–

* All Fe recalculated as FeO.

Column 1: Using classical methods, E. Jarosewich, analyst; trace elements by X-ray fluorescence by J. R. Cann and coworkers.

Column 2: Average ocean-floor basalt (Cann, 1971), 94 analyses; Fe_2O_3, FeO, H_2O +, H_2O−, and trace element averages (Melson and Thompson, 1971).

Column 3: Standard deviations for column 2.

Column 4: Average of 181 olivine tholeiites and tholeiites from the Hawaiian Islands (MacDonald and Katsura, 1964). Recalculated on an anhydrous basis.

Column 5: Average of 10 samples of alkali basalt from submarine volcanoes and islands of the eastern Pacific Ocean (Engel, et al., 1965). Recalculated on an anhydrous basis.

(Table 1). The ferric to ferrous iron ratio is considerably greater than fresh oceanic basalts, and reflects submarine oxidation. The water content, on the other hand, is higher (2.43 versus 1.08) than most midocean ridge basalts (Table 1). Weathering of deep-sea basalts commonly produces potassium-rich smectite (Melson and Thompson, 1973) which significantly increases the bulk K_2O content of even slightly weathered submarine basalts. Although clay minerals are abundant in the mesostasis, the K_2O content of the sample, 0.37 percent, is barely higher than the average for fresh ocean-floor basalt (0.22, Table 1).

TABLE 2.—Trace element composition (ppm) of the Adak Fracture Zone high-alumina basalt compared to other regions (all data and averages by Dr. J. R. Cann and colleagues; averages from Pearce and Cann, 1971)

Sample

Ti

Rb

Sr

Y

Zr

Nb

Adak Basalt

USNM 112471

10012

7.2

148

57

111

0.8

USNM 112472

−

9.7

144

49

108

4.2

Average Ocean floor basalt

7760

−

−

27

80

−

Average Island are andesite

4050

−

−

21

106

−

Average Hawaii Basalt

15360

−

−

24

162

−

In this region of the Adak Fracture Zone old oceanic crust formed by sea-floor spreading at the northern extension of the east Pacific rise about 63 million years ago? Or, is the seamount from which it was dredged the product of much younger, off-ridge volcanism? These two modes of origin correlate with distinct differences in chemical composition. A number of elements whose concentrations commonly differ in these two settings were determined in the Adak sample. These include Ti, K, and Zr, which are characteristically higher in volcanic islands and seamounts compared to deep-sea basalts from spreading ridges.

The most striking compositional differences between the Adak Fracture Zone basalt and most ocean-floor basalts, are its high alumina content, low magnesia content, and high total iron to magnesia ratio. These features are probably not a result of weathering. The Zr and Ti contents are transitional between seamount basalt and basalt derived from spreading centers (Table 2). Chemically, it is thus not clear to which category the Adak Fracture Zone basalt belongs.

If actually derived from a spreading center about 63 million years old, its chemically and perhaps even bathymetric corresponding half would be identifiable on the opposite side of the spreading center at magnetic anomaly 25. This test of a sea-floor spreading origin for the basalt cannot be made because the eastern counterpart of the region from which the Adak basalt may have come has long since been subducted beneath North America.

Origin of High-Alumina Content

High-alumina content can be a feature of erupted liquid, or a reflection of an abundance of already present calcic plagioclase phenocrysts. In the Adak high-alumina basalt, the high-alumina content is a reflection of a high-alumina liquid composition. Although large rounded plagioclase crystals occur, they compose on the order of 3 volume percent of the samples, an amount much too small to account for the high-alumina content of the sample. The large, rounded calcic plagioclase crystals are probably cognate, and may reflect convective movements or settling of early forming plagioclase crystals from cooler to hotter portions of the pre-eruption magma chamber.

Literature Cited

Bender, M. L., T. Ku, and W. Broecker

1966. Manganese Nodules: Their Evolution. Science, 151: 325–328.

Cann, J. R.

1971. Major Element Variations in Ocean-Floor basalts. Philosophical Transactions of the Royal Society of London, A.268:495–505.

Engel, A. E. J., C. G. Engel, and R. G. Havens

1965. Chemical Characteristics of Oceanic Basalts and the Upper Mantle. Geological Society of America Bulletin, 76:719–734.

Ericksson, B. H., and P. J. Grim

1969. Profiles of Magnetic Anomalies South of the Aleutian Island Arc. Geological Society of America Bulletin, 80:1387–1389.

Grim, P. J., and B. H. Ericksson.

1969. Fracture Zones and Magnetic Anomalies South of the Aleutian Trench. Journal of Geophysical Research, 74:1488–1494.

Heirtzler, J. R., G. O. Dickson, E. M. Herron, W. C. Pitman III, and X. Le Pichon

1968. Marine Magnetic Anomalies, Geomagnetic Field Reversals, and Motions of the Ocean Floor and Continents. Journal of Geophysical Research, 73: 2119–2136.

Ku, T., and W. S. Broecker

1967. Uranium, Thorium and Protactinium in a Manganese Nodule. Earth and Planetary Science Letters, 2:217–320.

MacDonald, G. A., and T. Katsura

1964. Chemical Composition of Hawaiian Lavas. Journal of Petrology, 5:82–133.

Melson, W. G., and G. Thompson

1971. Petrology of a Transform Fault Zone and Adjacent Ridge Segments. Philosophical Transactions of the Royal Society of London, A.268:423–441.

1973. Glassy Abyssal Basalts, Atlantic Sea Floor near St. Paul’s Rocks: Petrography and Composition of Secondary Clay Minerals. Geological Society of America Bulletin, 84:703–716.

Pearce, J. A., and J. R. Cann

1971. Ophiolite Origin Investigated by Discriminant Analysis Using Ti, Zr, and Y. Earth and Planetary Science Letters, 12:339–349.

Somayujulu, B. L. K.

1967. Beryllium-10 in a Manganese Nodule. Science, 156: 1219–1220.

Composition of Three Glass Phases in an Apollo 15 Basalt Fragment

George S. Switzer

ABSTRACT

The fragment studied contains glass of three distinct types: A: colorless, high silica glass; B: brown, high-iron interstitial glass. Microprobe analyses show high-iron interstitial glass. Microprobe analyses show there has been strong partitioning of certain elements, especially of K into the high-silica glass, and P and Ti into the high-iron glasses. The high-iron glasses are thought to have been formed as immiscible liquids.

George S. Switzer, Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20560.

Introduction

Some silicate liquids on cooling separate into two or more liquids of markedly different compositions. This process, generation of immiscible liquids, may be an important process in the generation of certain classes of igneous rocks, such as those in the syenitic and granitic families (Roedder, 1951; Philpotts and Philpotts, 1969; Roedder and Weiblen, 1970). Immiscibility has long been known in certain experimentally studied systems (Greig, 1927; Roedder, 1951), but was first documented in natural materials in Apollo 11 basaltic rocks (Roedder and Weiblen, 1970). Here I describe one of the best examples of liquid immiscibility yet reported in lunar samples.

During a study of Apollo 15 soil sample 15272,11 an unusual basalt fragment was encountered that contains glass of three distinct types, which for convenience are designated types A, B, and C: A is a colorless, high-silica glass; B is brown, high-iron blebs immiscible in A; and C is a brown, high-iron interstitial glass.

The sample is an angular, 2.0 mm fragment composed primarily of plagioclase, orthopyroxene, glass, cristobalite, ilmenite, and clinopyroxene, in that order of abundance. The density of the fragment is > 2.90 < 3.00. A photomicrograph is shown in Figure 1.

Microprobe analyses and microscopic examination yielded the following data on the principal minerals. Plagioclase crystals up to 0.2 × 0.8 mm in size have a composition near An_86, with slightly more sodic (An_83) rims. The orthopyroxene, in crystals up to 0.5 mm, has composition En_75Fs_25Wo_2. A single crystal of clinopyroxene is En_34Fs_26Wo_40.

FIGURE 1.—Thin section of basalt fragment from Apollo 15 soil sample 15272.11. Maximum dimension of fragment 2.0 mm. Transmitted light.

FIGURE 2.—Ilmenite crystal surrounded by interstitial Type C glass except where in contact with plagioclase. Area on left with mosaic structure is cristobalite. Note darkening of glass due to reaction with ilmenite. a, Transmitted light. b, Reflected light. Length of bar = 0.1 mm.

The cristobalite shows typical mosaic structure. Droplets of iron and possibly some sulfide are scattered throughout the specimen. The ilmenite contains 2.8 percent MgO.

Ilmenite-Glass Reaction

Ilmenite is a prominent phase (about 5 volume percent). Where ilmenite is in contact with Type C glass, the glass is frequently dark brown to opaque, with the depth of color decreasing away from the contact, as though ilmenite has reacted with the glass (Figure 2a, b). A microprobe step scan for Fe and Ti at 2µm intervals across an ilmenite-glass contact (along A-A’ of Figure 3a) yielded the data plotted in Figure 4. There has been some reaction between the two phases, but an apparent more extensive reaction seen in the thin

FIGURE 3.—Ilmenite crystal in contact with (to left) Type C interstitial glass, and (to right) with high-silica glass (Type A) with high-iron (Type B) immiscible blebs. A-A’ is line along which step scan analysis was made (see Figure 4). a, Transmitted light. b, Reflected light. Length of bar = 0.1 mm.

FIGURE 4.—Microprobe step scan for Fe and Ti along A-A’ of Figure 3.

FIGURE 5.—Large area of immiscible glass (left) consisting of high-silica colorless glass (Type A) with blebs of high-iron (Type B) glass. Right half of each photograph is same area as shown in Figure 3. a, Transmitted light. b, Reflected light. Length of bar = 0.1 mm. Circular, highly-reflective area in upper left is iron.

TABLE 1.—Composition of glass phases

section is due to inclined grain boundaries in a section that is approximately 40 μm thick.

The Glass Phases

Microprobe analyses of the three glasses are given in Table 1. The analyses were made using close standards and corrected by use of the ABFAN program of the Geophysical Laboratory (Boyd, et al., 1969). For comparison are given compositions of immiscible glass in Apollo 11 and 12 rocks described by Roedder and Weiblen (1971).

The areas of high-silica glass with immiscible blebs of high-iron glass (Figure 5a, b) are similar to those described in Apollo 11 and 12 rocks by Roedder and Weiblen (1970, 1971). Comparison of the high-silica glasses (Table 1, columns 1, 4, and 5) shows them to be similar, and characterized (in addition to high-silica), by low iron, calcium, and magnesium, and high potassium.

The correspondence between analyses of the brown immiscible blebs (columns 2, 6, and 7) is not

FIGURE 6.—Area of Type C high-iron glass interstitial to plagioclase and surrounding crystal of ilmenite. Triangular area above is high-silica glass (Type A) with high-iron glass blebs (Type B). a, Transmitted light. b, Reflected light.

as close. However, it should be pointed out that Roedder and Weiblen’s analyses of high-iron glasses in Apollo 11 and 12 rocks are averages of seven and five analyses, repectively, with a range in SiO_2 of 36.5–50.2 percent (for Apollo 11), and 40.0–45.0 (for Apollo 12). These authors point out that the high-iron glass in their samples varied somewhat in composition between samples, between blebs, and even within blebs. The new analysis presented here for Apollo 15 is of a single 20µm diameter bleb.

An analysis of the high-iron Type C glass is given in Table 1, column 3. This glass is clear and vitreous and typically interstitial (Figure 6), and quite distinct in this latter feature from the Type B immiscible blebs. It also differs chemically from Type B, as can be seen by comparison of columns 2 and 3 of Table 1.

Discussion

Apollo 15 glass analyses in Table 1 show that there has been strong partitioning of certain elements into one or the other liquid, the same as found by Roedder and Weiblen (1970, 1971) in their studies of immiscible glasses in Apollo 11 and 12 rocks. Of particular interest is the high concentration of K in the high-silica glass and the high concentration of P in the high-iron glasses. The depletion of phosphorus in the high-silica (granitic) fraction is a reverse trend to that in normal fractional crystallization and is thought to be the result of the separation of the liquids by immiscibility (Anderson and Greenland, 1969, and Roedder and Weiblen, 1970, 1971).

Because phosphorus is enriched in both types (B and C) of high-iron glasses described here, one can conclude that both were formed as immiscible liquids. The question then is why one of the two high-iron glasses occurs as blebs in high-silica glass, and the other interstitial to the plagioclase and pyroxene. One possible explanation is that, due to a complex cooling history, initially two immiscible liquids formed, of compositions (A + B) and C. Then on further cooling (A + B) further separated into Type B blebs immiscible in Type A.

Literature Cited

Anderson, A. T., and L. P. Greenland

1969. Phosphorus Fractionation Diagram as a Quantitative Indicator of Crystallization Differentiation of Basaltic Liquids. Geochimica and Cosmochimica Acta, 33:493–505.

Boyd, F. R., L. W. Finger, and F. Chayes

1969. Computer Reduction of Electron-probe Data. Carnegie Institution Year Book 67, Annual Report of the Director, Geophysical Laboratory, pages 210–215.

Greig, J. W.

1927. Immiscibility in Silicate Melts. American Journal of Science, series 5, 13:1–44.

Philpotts, A. R., and J. A. Philpotts

1969. Liquid Immiscibility Between Syenitic and Gabbroic Magmas (Abstract). Geological Society of America Abstracts 1969, pages 176–177.

Roedder, E.

1951. Low Temperature Liquid Immiscibility in the System K_2O–FeO–Al_2O_3–SiO_2. American Mineralogist, 36:282–286.

Roedder, E., and P. W. Weiblen

1970. Lunar Petrology of Silicate Melt Inclusions, Apollo 11 Rocks. Pages 801–837 of volume 1 in A. A. Levinson, editor, Proceedings of the Apollo 11 Lunar Science Conference, Houston, Texas, January 5–8, 1970. Geochimica and Cosmochimica Acta, supplement 1, volume 34.

1971. Petrology of Silicate Melt Inclusions, Apollo 11 and Apollo 12 and Terrestrial Equivalents. Pages 507–528 of volume 1 in A. A. Levinson, editor, Proceedings of the Second Lunar Science Conference, Houston, Texas, January 11–14, 1971. Geochimica and Cosmochimica Acta, supplement 2.

Petrographic Analysis of Apollo 16 Samples 66083,1 and 67943,1

Brian Mason

ABSTRACT

Two samples of 2–4 mm fines collected on the Apollo 16 mission consist largely of fragments of anorthositic rock and breccias derived therefrom.

Brian Mason, Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20560.

Sample 66083,1 was a 0.5 g sample of 2–4 mm fines from a clod of white impact ejecta collected at Station 6 on the southwest wall of a subdued 10 m crater on the lowest “bench” of Stone Mountain, near its base; the astrogeology report (Apollo 16, 1973) says “possibly from South Ray crater, but location generally shadowed from South Ray crater ejecta.”

The sample as received contained 12 fragments > 2 mm, with a total weight of 0.433 g, and an average weight of 0.036 g; there was 0.066 g of material < 2 mm. The > 2 mm fragments were density-fractionated in methylene iodide-acetone liquids, with the results as shown in Table 1. Polished thin sections were made of fragments B, C, D, E, F, and of one from 60083,1 A (designated as 66083,1AA). Half of fragments AA and F were ground and fused with lithium tetraborate flux, and the resulting glasses analyzed with the micro-probe, with the results given in Table 2. A polished thin section (66083,1H) was also prepared from the 0.2–0.4 mm material obtained by sieving from the coarser fragments; this material contained 334 individual particles, which were classified as shown in Table 3. There appears to be a continuous sequence between breccia and crystalline rock fragments, and for some fragments the assignment to one class or the other is to some degree arbitrary.

Microprobe analyses of mineral grains gave the following results (number of grains analyzed in parentheses): plagioclase (10): An88–97, mean An_93; olivine (4): Fa20–25, mean Fa_23; orthopyroxene (6): Wo2–4, Fs21–26, mean Wo_3Fs_25; augite (1): Wo_41Fs_11 En_48. Six glass fragments were also analyzed, with the results as shown in Table 4. Glasses 1, 2, and 3 could be melted regolith from this site; 2 and 3 are very similar to AA in Table 2, while 1 is somewhat more feldspathic. Glass 6 corresponds to a completely melted mare basalt. The interpretation of the compositions of glasses 4 and 5 is not so clear-cut, and they probably represent mixtures of different components.

The petrography of the fragments larger than 2 mm is as follows:

AA. A breccia with a glassy matrix containing about 20–30 percent of crystal fragments. The fragments are predominantly plagioclase (maximum

TABLE 1.—Density-fractionation results for 66083,1

Fragment

Density

Number of fragments

Grams

A

<2.70

7

0.208

B

2.72

1

0.030

C

2.85

1

0.042

D

2.90

1

0.029

E

3.03

1

0.025

F

3.07

1

0.099

Total

12

0.433

TABLE 2.—Analyses and norms of two fragments from 66083,1 (analyst: J. Nelen)

Constituent

AA

F

ANALYSES

SiO_2

44.8

47.3

TiO_2

0.62

0.92

Al_2O_3

25.5

19.2

Cr_2O_3

0.14

0.18

FeO

5.76

9.20

MnO

0.12

0.16

MgO

6.11

9.86

CaO

14.7

11.4

Na_2O

0.52

0.59

K_2O

0.18

0.32

P_2O_5

0.1

0.3

Total

98.6

99.4

NORMS

An

66.4

48.8

Ab

4.4

5.0

Or

1.1

1.9

Di

4.7

4.9

Hy

13.5

31.6

Ol

6.6

3.9

Il

1.2

1.8

Ap

0.2

0.7

Cr

0.2

0.3

AA = fragment with D<2.70; F = fragment with D = 3.07.

size 0.3 mm), with minor olivine and orthopy-roxene, and some lithic fragments, also mainly plagioclase. Some of the plagioclase fragments show bending of the twin lamellae. This fragment appears to be typical for the material with D <2.70; its analysis (Table 2) is very similar to that of fines

TABLE 3.—Classification of 334 particles from 66083,1H

Particles

Number

Percent

Crystalline rock fragments

126

37.7

Breccia fragments

125

37.4

Glass (clear and devitrified)

36

10.8

Plagioclase fragments

31

9.3

Plagioclase, partly melted

8

2.4

Spherules, glass or devitrified

7

2.1

Metal fragment

1

0.3

Total

334

100.0

TABLE 4.—Analysis of six glass fragments from 66083, 1H

from the same location (66081, H. Rose pers. comm.), indicating that it represents partially melted soil.

B. A fragment of partly devitrified glass, with some plagioclase fragments (maximum size 0.1 mm) in one area; one spherule of metal, 0.1 mm diameter, was noted.

C. A fine-grained feldspar-rich rock, made up of a felted aggregate of small plagioclase laths (up to 0.01 mm long) with about 10 percent of interstitial pyroxene and olivine; and minor amounts of opaques (probably ilmenite); occasional larger equidimensional grains of plagioclase (up to 0.1 mm) are also present. The texture suggests a recrystallized breccia, with the larger plagioclase grains being relict fragments from a coarse-grained rock.

D. A breccia consisting of clasts of plagioclase (up to 0.25 mm) and plagioclase-rich rock (up to 2 mm) in a fine-grained microcrystalline feldspathic groundmass; four metal spherules, the largest 0.35 mm in diameter, are present. Microprobe analyses give an average plagioclase composition of An_90 (range An_88-An_94); four pyroxene grains show a range of Wo4.3–11.6, Fs17.6–22.0; one grain of olivine gave Fa_29.

E. A fragment consisting of plagioclase clasts (up to 0.3 mm) in a fine-grained groundmass of plagioclase and ferromagnesians (olivine and pigeonite) in subequal amounts, with some opaques (ilmenite and a few metal grains); the texture of the groundmass suggests that it may represent a recrystallized glass. Microprobe analyses of the individual minerals (number of grains analyzed in parentheses) gave plagioclase (9), An_84–An_95, mean

TABLE 5.—Density-fractionation results for 67943,1

Density

Number of fragments

Grams

<2.70

2

0.061

2.70–2.80

6

0.051

2.80–2.90

5

0.199

2.90–3.00

3

0.049

An_90; pigeonite (7), Wo8–12, Fs22–24, mean Wo_9,Fs_23; olivine (14), Fa25–27, mean Fa_26.

F. A crystalline rock made largely of subequal amounts of plagioclase and ferromagnesians (pyroxenes and olivine), with a minor amount of opaque material (mainly ilmenite, but with some prominent metallic spherules up to 0.4 mm in diameter). There are distinct areas of different grain size, suggesting the rock is a recrystallized breccia of lithic and mineral fragments; this is supported by the presence of occasional large (up to 0.4 mm) plagioclase grains, probably por-phyroclasts.

Microprobe analyses of the individual minerals gave the following results (number of grains analysed in parentheses): plagioclase (12): An90–98, mean An_95; olivine (18): Fa38–43, mean Fa_41; orthopyroxene (17): Wo3–7, Fs25–32, mean Wo_4Fs_28; pigeonite (6): Wo10–12, Fs30–31, mean Wo_11Fs_31; augite (18): Wo34–40, Fs16–20, mean Wo_37Fs_17; metal (7): Ni 4.7–6.5 percent, mean 5.1 percent, and Co 0.58–0.77 percent, mean 0.67 percent.

The analysis (Table 2) shows that the fragment is of noritic composition, but the texture is hornfelsic rather than igneous, suggesting recrystallization of a norite breccia at high temperatures (perhaps high enough to produce a metal-sulfide melt, represented by the metallic spherules, but not high enough to melt the silicates). The fragment is very similar in composition and texture to 65015, a 1.8 kg rock collected at the adjacent Station 5 and ascribed by the Geology Investigation Team to South Ray crater ejecta.

Sample 67943,1 was a 0.5 g sample of 2–4 mm fines, one of the sieve fractions from 67940, a soil sample collected from the House Rock area on the southeast of North Ray crater (Station 11 of the Apollo 16 traverses).

The sample as received contained 16 fragments >2 mm, with a total weight of 0.453 g, and an

TABLE 6.—Analyses and norms of three fragments from 67943 (analyst: J. Nelen)

Constituent

D = 2.70–2.80

D = 2.70–2.80

D = 2.80–2.90

ANALYSES

SiO_2

44.9

43.4

44.6

TiO_2

0.42

0.35

0.44

Al_2O_3

29.6

29.2

27.9

FeO

3.52

3.58

4.29

MnO

0.05

0.08

0.07

MgO

3.22

3.24

5.43

CaO

16.8

16.4

15.4

Na_2O

0.68

0.60

0.67

K_2O

0.10

0.09

0.15

Total

99.3

96.9

99.0

NORMS

An

77.6

76.6

72.4

Ab

5.8

5.1

5.7

Or

0.6

0.6

0.9

Di

4.9

3.9

3.2

Hy

4.8

3.5

6.1

Ol

4.9

6.4

9.5

Il

0.8

0.7

0.8

An

93

93

91

Fa

35.8

36.8

29.8

Pyx

Ca_25Mg_48Fe_27

Ca_26Mg_47Fe_27

Ca_17Mg_58Fe_25

average weight of 0.029 g; there was 0.047 g of material <2 mm. The >2 mm fragments were density-fractionated in methylene iodide-acetone liquids, with the results as shown in Table 5. Compared to 66083, another sample of 2–4 mm fines analyzed, this sample shows a smaller density range, and a concentration of material where D = 2.70–2.90.

Polished thin sections were made of 11 fragments covering the full density range; for three of them sufficient material remained after sectioning for microprobe analysis after fusion with lithium tetraborate flux, and the results are given in Table 6.

Except for two fragments in the D = 2.90–3.00 fraction, the individual fragments could all be classed as brecciated anorthosites; they differed one from another mainly in the amount of glass in the matrix, the lower density fragments having larger amounts of glass. This glass was usually pale brown and isotropic, sometimes showing incipient devitrification. The analyses in Table 6 confirm the anorthositic composition of these fragments; they all show over 80 percent normative plagioclase of anorthite composition, with minor amounts of olivine and pyroxene.

Of the two non-anorthositic fragments, both with density between 2.90 and 3.00, one was an equigranular plagioclase-rich microgabbro, with individual grains averaging 0.1 mm across. The estimated mineral composition is 65 percent plagioclase (An_94), 15 percent olivine (Fa_19), 15 percent pigeonite (Wo_12Fs_23En_65), and 5 percent opaques (mostly ilmenite). The compositions given for the minerals are averages of microprobe analyses; plagioclase and olivine are very uniform in composition, whereas pigeonite shows minor variability from grain to grain.

The other non-anorthositic fragment appeared to be a composite particle, consisting of a relatively coarse (plagioclase grains up to 0.6 mm) troctolite welded to a fine-grained (maximum grain size 0.1 mm) gabbroic anorthosite. However, the mineralogy of the two parts of the fragment are identical—plagioclase (An_94), olivine (Fa_21), minor hyper-persthene (Fa_19), and a little opaques—and the fine-grained material may be comminuted and recrystallized troctolite. The boundary between the two parts is quite sharp.

These two non-anorthositic fragments may represent primary igneous rocks from the Apollo 16 site that have escaped the ubiquitous brecciation and recrystallization so characteristic of most of the rocks collected on this mission. Alternatively, they may be exotic fragments transported to the Apollo 16 site from some other region on the Moon.

ACKNOWLEDGMENT.—This research was supported by a grant from the National Aeronautics and Space Administration (NGR 09–015–146).

Literature Cited

Apollo 16 Preliminary Examination Team

1973. The Apollo 16 Lunar Samples. Science, 179:23–34.

The Allende Meteorite: Chondrule Composition and the Early Histroy of the Solar System

Andrew L. Graham

ABSTRACT

Fifty chondrules and aggregates from the Allende meteorite (Type III carbonaceous chondrite), have been analyzed for the major elements using a fusion technique and subsequent microprobe analysis of the resulting glass bead. A portion of each sample was retained and made into a polished thin section for mineralogical studies. The major element chemistry suggests that the Ca/Al-rich chondrules and aggregates exhibit compositional changes, whereas the Mg/Fe-rich chondrules do not. There appears to be no simple relationship between these two chondrule groups. Concomitant with a decrease in the (CaO + Al_2O_3) content is a decrease in TiO_2 and an increase in Na_2O. This is paralleled by changes in the mineralogy of the chondrules. Although the (CaO + Al_2O_3) to TiO_2 relationship is that which has been predicted in terms of a condensing solar nebular model, that of (CaO + Al_2O_3) with Na_2O does not conform to this model. Other evidence against the primary nature of the Ca/Al-rich Allende chondrules is cited.

Andrew L. Graham, Department of Mineralogy, British Museum (Natural History), London S.W. 7, England.

Introduction

The Allende meteorite is a Type III carbonaceous chondrite of the Vigarano subgroup (Clarke, et al., 1970). It is composed of chondrules and microcrystalline aggregates distributed heteroge-neously throughout a black, olivine-rich matrix. Some of the chondrules and aggregates contain minerals rarely found in meteorites. These include melilite, magnesian spinel, fassaite, wollastonite, cordierite, hibonite, and grossular (Clarke, et al., 1970; Fuchs, 1969, 1971; Marvin, et al., 1970). From a possible composition of the primitive (that is, undifferentiated), solar nebular gas (e.g., table in Cameron, 1968:127), and making assumptions as to the initial temperature of this gas, the condensation sequence with falling temperature of stable molecules can be calculated. Such calculations (Lord, 1965; Grossman, 1972) indicate that corundum, spinel, and melilite form early in this sequence. It is, therefore, tempting to suggest that the occurrence of these minerals in Type III carbonaceous chondrites is evidence supporting the thermodynamically derived condensation sequence. It is not at present known whether the Ca/Al-rich aggregates and the melilite-bearing chondrules of the Allende and similar meteorites are “bulk primary” condensates or not. Does their bulk composition represent a quasiequilibrium state, similar to that shown by terrestrial igneous processes, in which the crystalline solids represent one side of an equilibrium solidification sequence, or are these chondrules and aggregates the result of the association of material after the condensation sequence had finished?

The structure and chemistry of the carbonaceous chondrites provide the basis for a strong argument against the metamorphism of these meteorites subsequent to their accretion. This is particularly shown by the wide variation in the Fe/Fe + Mg of the olivines they contain, and by the presence of glass within the chondrules. The bulk chemistry of the chondrules has not, therefore, been changed by metamorphism since the formation of the meteorite. In this work chondrules and aggregates separated from the Allende meteorite have been analyzed for their major elements to see whether there is a sequential relationship in their chemistry. Do they represent particular stages in the condensation

TABLE 1.—The composition of some chondrules and aggregates from the Allende meteorite

of the nebular gas or are they random associations which have been formed for material produced by this primitive condensation? If the latter is the case then no chemical trends would be expected, while if the former is the case then a sequential chemistry may be shown.

ACKNOWLEDGMENTS.—This work was performed during the tenure of a Smithsonian Research Fellowship. Dr. B. Mason and Dr. R. F. Fudali are thanked for their assistance and also Dr. L. Walter who gave advice on the analytical procedure used. The constructive criticism and suggestions of Dr. A. A. Moss and Dr. R. F. Fudali much improved the manuscript.

Method

Chondrules and aggregates were picked from fractured faces of specimens of the Allende meteorite. The aggregates, which are friable, were removed from the bulk material with a stainless steel needle. Each sample was then crushed in an agate mortar. An aliquot of between 1 and 2 mg was mixed with 2.5 times its weight of a lithium tetraborate/lithium carbonate flux prepared according to the method of Norrish and Hutton (1969). The mixture was fused to a glass bead in a small gold crucible by maintaining it at 960° C for five minutes in a vertical quench furnace. After quenching, the bead was mounted in a lucite disc, polished and analyzed for nine elements in an A.R.L. EMX electron microprobe. United States Geological Survey standards Wl, AGV1, DTS1 and the Allende bulk standard were prepared in the same way and used as standards. The homogeneity of the standards and unknowns was checked by performing multiple analyses of the standards and three separate analyses of each unknown. Reproducibility of the whole procedure was checked by making six separate beads of a standard and analyzing each as an unknown. The relative mean deviation of the analyses in this case was ±3 percent for elements present in the undiluted material at concentrations greater than 0.5 percent by weight. Summation to 100 percent was also used as a test; any analysis that did not total 100 ± 2 percent was rejected. The values used for the composition of the USGS standards were those given by Flanagan (1969), and those of the Allende bulk standard were given in Clarke, et al. (1970).

Results

The analyses of 50 chondrules and aggregates have been used to plot Figures 1–3 and in Table 1 representative analyses are quoted for eight individual samples. The mineralogy of most of the samples was examined by preparing a thin section from a fragment of each. Analyses 1–3 of Table 1 are of Mg/Fe-rich chondrules. Analyses 4 and 5 are of fine-grained aggregates; these are too fine for microscopic identification of their constituent minerals, but x-ray powder diffractrograms show the presence of clinopyroxene, melilite, and spinel.

FIGURE 1.—Ternary plot of SiO_2 against (CaO + Al_2O_3) and (FeO+MgO), all in weight percent, for the chondrules and aggregates from the Allende meteorite. The line shown is a possible fractionation trend.

■ well crystallized Ca/Al-rich chondrules

□ finely crystalline aggregates

▲ olivine-rich chondrules

Analyses 6–8 are of coarse-grained chondrules composed of melilite and clinopyroxene with minor spinel. The composition of a melilite and some clinopyroxenes from similar chondrules are given in Clarke, et al. (1970) and in Marvin, et al. (1970).

Figure 1 is a ternary plot of (CaO + Al_2O_3) against SiO_2 and (MgO + FeO) for the data obtained in this work. FeO was combined with MgO as most of the analyses showed less than 5 percent FeO, except for the olivine chondrules in some of which the FeO content rises to 14 percent. From the distribution of points it can be seen that there are two chondrule/aggregate groups. One shows evidence for a development trend, that is to say its composition could be regarded as changing regularly in some manner, but the second shows no such vector properties in the diagram. The former group is made up of the Ca/Al-rich bodies and the latter of chondrules containing olivine and orthopyroxene and, occasionally, glass. The group with a trend in bulk chemistry also shows a corresponding mineralogical development. At the Ca/Al-rich end, the chondrules are composed predominantly of gehlenite with a little spinel and clinopyroxene. Progressing from this extreme towards the (MgO + FeO)-SiO_2 join the following trends are observed:

This is accompanied by a decrease in the TiO_2 content and an increase in the Na_2O content of the chondrules. The concentration of K_2O is too low to be meaningful with the analytical method used. Figure 2 shows the distribution of TiO_2 contents. The average concentration of TiO_2 in the melilite plus clinopyroxene chondrules is 1.2 percent, and this decreases on moving from the most Ca/Al-rich compositions plotted in Figure 1 towards the SiO_2-(FeO + MgO) join. The olivine chondrules show a uniform TiO_2 content of around 0.2 percent by weight. The changes in the concentration of Na_2O in the same sequence is more complex, as shown in Figure 3. The maximum Na_2O content is observed in those chondrules whose compositions plot in the middle of Figure 1; the MgO + FeO-rich chondrules are almost as low in Na_2O as are the gehlenite-rich bodies. Petrographic examination of the thin sections confirms the distinction between the two groups shown in Figure 1. The group richest in CaO and Al_2O_3 contains soda-free melilite and clinopyroxene with spinel and occasionally

FIGURE 2.—A histogram of TiO_2 concentrations in Allende chondrules and aggregates. The peak at 1.2 percent TiO_2 occurs at the Ca/Al-rich end of the line drawn on Figure 1.

FIGURE 3.—A histogram of Na_2O concentrations in Allende chondrules and aggregates. The peak at about 0.2 percent Na_2O is due to the melilite chondrules and that at 0.6 percent Na_2O to the olivine chondrules.

anorthite while the other group contains olivine and orthopyroxene with occasional glass. The coexistence of olivine and melilite was not seen nor was that of olivine and clinopyroxene. A further interesting observation, not expected from experience with terrestrial samples, is the coexistence of anorthite and melilite. Schairer and Yoder (1969) reported the coexistence of these minerals in experimental runs and commented that this had not, so far, been observed in nature.

Discussion

The distinctive petrographic and chemical differences between the Ca/Al-rich chondrules and aggregates and the Mg/Si-rich chondrules strongly suggest that there was very little brecciation and mixing of chondrule fragments prior to their incorporation in this meteorite. It is, therefore, possible to regard the bulk composition of the Ca/Al-rich chondrules and aggregates as being that of the solid phases of a fractionation sequence and so any trends in their major element chemistry can be interpreted as reflecting changes in the composition of their parent material. Changes in the pressure and temperature of the parent material, the nebular gas of the condensation hypothesis, will have very little effect upon this relationship, since dP/dT for the vapor to solid transition for melilite, enstatite, forsterite, and spinel is almost constant over a pressure range of 10−7 to 10−2 atmospheres, and has very nearly the same value for all these phases (Grossman, 1972). A further point is that fine-grained aggregates are similar in composition to the more coarsely crystalline Ca/Al-rich chondrules. It is not possible to distinguish between them in terms of those elements used to construct Figure 1. This may, in part, be due to the small number of analyses, data for only six fine-grained aggregates being currently available, but these all plot within the field defined by the analyses of the coarse-grained Ca/Al-rich chondrules. The implication is that either the conditions favoring the crystallization of material from a similar parent were not uniform during the formation of the Ca/Al-rich bodies, or that subsequent recrystallization of the first-formed microcrystalline aggregates produced the coarsely crystalline chondrules. Evidence suggesting that some recrystallization has occurred comes from the Rb/Sr systematics of the Ca/Al-rich bodies. They do not define a single isochron (Gray, et al., 1973), implying that there has been some movement of Rb and/or Sr since their formation. It has been shown, however, that the chondrule olivines show radiation damage whereas the matrix olivines do not (Green, et al., 1971). Since this damage is removed by heating to about 500° K (Green, et al., 1971), the chondrule olivines must have remained below this temperature during and after the accretion of the meteorite. Further, the presence of grossular in some of these aggregates (Clarke, et al., 1970) and of andradite (Fuchs, 1971) implies temperatures of the order of 700° K. Grossular has been synthesized at 800° C from a glass (Yoder, 1954) and at 400° C from a mixture of 3SiO_2-Al_2O_3−3CaCO_3 (Christophe-Michel-Levy, 1956). Thus an upper temperature limit of about 700° K can be given for the postformation history of the Ca/Al-rich bodies of this meteorite, and of about 500° K for the Mg/Fe-rich chondrules. These temperatures are too low to cause the formation of the coarse-grained chondrules from the finegrained aggregates by recrystallization during or after the accretion of the meteorite.

The changes in the bulk chemistry of the two chondrule types, Ca/Al-rich and Mg/Fe-rich, are such that it is not possible at present to connect them unequivocally into a single fractionation sequence with a common parent. It may be that any sequential change in the Mg/Si ratio of the olivine-rich chondrules that developed as a result of early condensation processes has been modified by subsequent exchange between these chondrules and the residual material prior to the accretion of the Allende meteorite. In particular, the magnesium silicates, enstatite, and forsterite will become more iron-rich by this process, which moves their composition toward the MgO + FeO apex of Figure 1. Plotting this figure on an iron-free basis does not, however, cause the magnesium-rich chondrules to plot on an extension of the line drawn; the distinction between the two groups of chondrules remains.

The alignment of chondrule compositions in the Ca/Al-rich portion of Figure 1 suggests that their bulk compositions were fixed by a fractionation sequence similar to that derived by Grossman (1972) from theoretical considerations of the primitive nebular gas. Fuchs and Blander (1973), however, give a summary of the phenomena that they have observed in Ca/Al-rich chondrules from the Allende meteorite that suggests a liquid precursor for these chondrules, rather than their formation from a vapor by direct condensation. In particular they note the spherical nature of the chondrules and the occurrence of eutectic intergrowths of pyroxene and anorthite and also gehlenite and anor-thite. Grossman and Clark (1973) maintain that the formation of any liquid took place after the main condensation sequence, from solids produced in this sequence. This is required by their theory because the calculated condensation sequence predicts the formation of some phases, for example clinopyroxene and anorthite, at temperatures that are below their solidi. The direct condensation hypothesis has difficulty in explaining the observed Mg/Si ratios of the Ca/Al-rich chondrules, which are almost constant during the decrease in (CaO + Al_2O_3) content (Figure 1). The direct condensation hypothesis predicts spinel as an early solid phase, subsequent condensates being more siliceous. There should then be a decrease in the Mg/Si ratio of the succeeding chondrules as condensation proceeds. This trend is not observed for the chondrule compositions plotted in Figure 1; actually there is a slight increase in this ratio.

The evidence from the Allende Ca/Al-rich chondrules suggests that, if they are “primary condensates,” they have had a more complicated history than simply that of condensation and incorporation into Type III carbonaceous chondrite matrix. How far this has erased evidence of the primitive state of these condensates is not clear. The great heterogeneity of the meteorite is remarkable and it may be that further samples will provide a better means for distinguishing between phenomena that could be produced by the early condensation sequence in the solar nebula, and those that are the result of processes subsequent to this event.

Literature Cited

Cameron, A. G. W.

1968. A New Table of Abundances of the Elements in the Solar System. Pages 125–143 in L. H. Ahrens, editor, Origin and Distribution of the Elements. New York: Pergamon.

Christophe-Michel-Levy, M.

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The Pulsora Anomaly: A Case against Metamorphic Equilibration in Chondrites

Kurt Fredriksson, Ananda Dube, Eugene Jarosewich, Joseph A. Nelen, and Albert F. Noonan

ABSTRACT

Four Indian H-group chondrites, Andura, Butsura, Pulsora, and Sitathali, with almost identical chemical composition but differing in texture and structure, are described. All have essentially the same and constant (“equilibrated”) olivine and pyroxene composition. Pulsora, however, contains lithic fragments, some of which are coarsely crystalline with almost no metal, while others contain skeletal olivine in silica-rich glass. Thus Pulsora could not have been “equilibrated” after the final agglomeration, nor is it necessary to postulate any such “metamorphic” equilibration to explain the texture and mineralogy of other chondrites.

Kurt Fredriksson, Eugene Jarosewich, Joseph A. Nelen, and Albert F. Noonan, Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, D. C. 20560, Ananda Dube, Geological Survey of India, Calcutta 13, India.

Introduction

Circumstances of fall, morphology, and general classification of the four Indian H-group chondrites, Andura, Butsura, Pulsora, and Sitathali, have been reported by Murthy, et al. (1969), who also referred to some previous work by Coulson (1940). A more detailed description of Sitathali was published by Viswanathan, et al. (1971). Andura and Butsura were grouped together by Murthy, et al., while according to Coulson (using the Rose, Tschermak, Brezina classification) they were respectively Cck, crystalline spherical, and Ci, intermediate chondrites. Pulsora and Sitathali were described by Murthy, et al (1969) as brecciated chondrites with “fine” and “coarse” matrix respectively and as Cib, brecciated intermediate, and Chob, brecciated howarditic chondrites by Coulson (1940). All four belong to the H-group (high iron) as defined by Urey and Craig (1953) and Keil and Fredriksson (1964). According to the subdivision, mainly on degree of “crystallinity,” proposed by Van Schmus and Wood (1967), Butsura is H6 and Sitathali H5. Andura and Pulsora have not been classified previously according to this system. However, by applying the criteria of Van Schmus and Wood, Andura is definitely within the H5–H6 range. Pulsora on the other hand shows a variety of features allowing it to be placed in any group from H3 to H6 similarly as the Hedjaz L-group chondrite (Kraut and Fredriksson, 1971).

These four meteorites were selected for detailed comparative studies from a number of meteorites currently being investigated under a joint program of the Geological Survey of India and the Smithsonian Institution, because of their essentially identical chemical composition in spite of gross morphological and textural differences as indicated by the studies referred to above as well as our data.

ACKNOWLEDGMENTS.—We are grateful to the Director General of the Geological Survey of India, Dr. M. K. Roy Chowdhury, as well as his predecessors for encouraging this cooperative work over many years. Mr. R. K. Sundaram and Drs. S. V. P. Iyengar and M. V. N. Murthy, all of the Geological Survey of India, also gave much assistance. For various data reductions we are indebted to the Smithsonian Information Systems Division and B.

FIGURE 1.—Photomicrograph of thin section of the Andura bronzite-chrondrite (H6). Only one chondrule, right center, is discernible; its boundaries are indistinct. Part of the matrix is relatively coarse and equigranular; other parts, however, are still fine-grained. White to gray are silicates; black, metal and troilite. Length of section 5 mm. Compare with frontispiece (a).

J. Fredriksson. This work has been supported in part by grants from the Smithsonian Research Foundation and NASA (NGR 09–015–207).

Mineralogy and Textures

Figures 1–4 and the frontispiece show low magnification photomicrographs of thin sections of the four chondrites. The distinction between Sitathali (H5), Andura (H5–6), and Butsura (H6) with regard to grain size, degree of crystallinity and “integration” between chondrules and matrix (Van Schmus and Wood, 1967) is clearly open to rather subjective judgment. Pulsora has parts similar in texture to the other three, but Figure 5 shows a relatively coarsely crystalline fragment within Pulsora with clear crystals of plagioclase (typical of Type 6), diopside and minor whitlockite. This fragment is also nearly devoid of metal and troilite, like so-called amphoterites, or LL-group chondrites, but its olivine is typical of the H-group (also nearly the same as in the main mass of Pulsora, see Tables 1, 5, and 6) and its texture is achondritic (perhaps a “Grade 7” in the Van Schmus and Wood (1967) 1

FIGURE 2.—Photomicrograph of thin section of the Butsura bronzite chondrite, classification H5 (towards H6). Chondrules are somewhat more discernible than in Figure 1, while the matrix shows some relatively fine-grained areas. Length of section 5 mm.

to 6 petrographic scale). The Pulsora section shown in Figures 6 and 7, on the other hand, includes a fragment (chondrule?) with skeletal to euhedral olivine in clear glass of the kind usually found only in Type 3 chondrites. The detailed composition and significance of these fragments are discussed further below.

Table 1 summarizes electron probe analyses of the major silicate phases, olivine, low and high calcium pyroxenes and plagioclase in the four meteorites. In addition, the modal composition was determined by point counting by probe analysis of (Fe, Ca, Mg) on a grid 0.3 × 0.3 mm. The calculated weight percentages of these four silicates are also indicated in Table 1. The complete modal analysis is reported in Table 3 and compared to the norm. The technique and the computer program used is described in the Appendix.

The phase compositions in Table 1 are averages from analyses performed at various times with different instruments and we estimate the accuracy to be at the best ±2 percent relative but usually better than ±6 percent.

Olivine: The iron value, which is the most reliable, is no more accurate than ±2 percent of the values given (this is about the best which can be

FIGURE 3.—Photomicrograph of thin section of the Sitathali bronzite chondrite (H5). The structure is similar to that shown in Figure 2. Chondrules, e.g., center and top left, are somewhat more abundant and distinct. Length of section 5 mm.

achieved by using a close standard and the Bence and Albee (1968) correction factors); this makes the olivines in all four chondrites essentially identical. The precision, however, while measuring olivine in a single sample is higher (±0.1% FeO), and relative differences in olivine composition in Pulsora are discussed below. Manganese, magnesium, and silicon were also measured but with less accuracy.

Pyroxenes: A calcium-poor orthopyroxene is the most abundant in all four meteorites and has essentially constant composition within each stone but small and probably real differences between the meteorites. Like the olivines they are relatively coarse, well defined and distinguishable in the modal analysis. The less abundant calcium-rich pyroxenes show greater chemical variations (especially in Pulsora), are fine-grained, and occur as inclusions in the other minerals (lamellae in Ca-poor pyroxenes) or intergrown with plagioclase in devitrified areas. Like the plagioclase they are, therefore, hard to distinguish during modal analysis (Appendix) and the average composition given in Table 1 is rather uncertain.

Plagioclase: This phase is almost impossible to identify microscopically (except in a fragment in

FIGURE 4.—Photomicrograph of thin section of the Pulsora bronzite chondrite. The classification for this section is H4 to H5, but compare also Figures 5 to 8, and frontispiece (b). Chondrules and lithic fragments, e.g., right center, are clearly visible in the mostly fine-grained, gray to opaque matrix. Large, coherent black areas are metal, troilite, and other opaque minerals. Length of section 5 mm.

Pulsora) and almost invariably contains pyroxene crystallites. The reported composition is based on the calcium content obtained in areas where iron and magnesium values approach minimum (~ background). In the modal analyses allowance was made for substantial apparent contents of magnesium and, especially, iron.

Metal, both taenite and kamacite, troilite and whitlockite were identified in our modal analyses and although numerous grains were analysed and counted detailed descriptions are not warranted because they are of average composition and abundance. Also, the absolute abundance of these phases can be estimated more accurately from the bulk chemical analyses. A number of common accessory minerals, e.g., chromite and ilmenite, as well as more exotic ones, like copper and spinels, were also identified (cf. Ramdohr, 1973) but these phases seem to contribute little to the understanding of current models for the origin of chondrites, especially ours involving impact-melting and brecciation.

TABLE 1.—Abundance and average composition of major silicate phases

Chemical Composition

The analyses reported in Table 2 are almost identical. Only Andura shows less metallic Fe and more FeO. Apparently some of its metal (and/or troilite) has been more susceptible to atmospheric oxidation. This assumption is strongly supported by the fact that the calculated normative fayalite content of the olivine, Fa_23 (Table 3), is considerably higher than the measured value, Fa_19 (Table 1), which is the same as in the three other stones. Andura also has a more “rusty” appearance both macroscopically and in thin section. Pulsora and Butsura seem to have higher carbon contents than the other two but the possibility of contamination cannot be entirely disregarded. (The analysis of Sitathali reported by Viswanathan, et al. (1971) is apparently erroneous, especially with regard to the iron content as the authors suspected.)

In Table 3 the normative and modal compositions are compared. The mode was obtained by electron probe analysis as described above and in the Appendix. The composition of the normative minerals agrees closely with the values obtained

TABLE 2.—Chemical composition (analysts: J. Nelen, Andura; and E. Jarosewich, Butsura, Pulsora, Sitathali)

Constituent

Andura

Butsura

Pulsora

Sitathali

Fe

13.72

16.61

17.23

16.08

Ni

1.62

1.75

1.78

1.79

Co

0.08

0.07

0.10

0.09

FeS

5.57

5.89

4.99

5.76

SiO_2

36.85

36.27

35.97

36.65

TiO_2

0.16

0.12

0.12

0.14

Al_2O_3

1.85

1.98

2.26

2.37

Cr_2O_3

0.53

0.56

0.52

0.43

FeO

12.23

9.65

10.58

9.96

MnO

0.39

0.31

0.29

0.31

MgO

23.42

23.21

22.77

23.45

CaO

1.97

2.00

1.59

1.71

Na_2O

0.91

0.85

0.84

0.87

K_2O

0.12

0.08

0.10

0.10

P_2O_5

0.29

0.31

0.26

0.30

H_2O+

0.19

0.53

0.00

0.10

H_2O−

0.10

0.13

0.10

0.06

C

0.05

0.15

0.14

0.05

Total

100.05

100.47

99.64

100.22

Total Fe

26.74

27.85

28.62

27.48

TABLE 3.—Normative and modal (weight percent) compositions

by probe analysis (except for the high Fa value in Andura, explained above). Although in the modal analysis only two pyroxenes were distinguished, i.e., those with <1% CaO (Pyroxene 1) and >1% CaO (Pyroxene 2), the average composition calculated according to Table 1 is Wo_10En_75Fs_15 while the normative pyroxenes (Table 3) are in the range Wo_6–9En_72–76Fs_18–19. The amount of pyroxene in the norm, however, is consistently lower than in the mode while the reverse is true for olivine and plagioclase. Because the “Residue” in the modal analyses is substantial, we have attempted to establish its chemical composition by deducting the elements in the modal minerals as well as normative metal, troilite, chromite, ilmenite, and apatite. In Table 4 these residues are compared with the chemical composition of the bulk silicates obtained by deducting FeO for ilmenite and chromite and CaO for apatite from the chemical analyses in Table 2. It seems clear that the residue is severely deficient in silica but enriched in alumina and alkalies. Since a large part of the residue in these finegrained rocks must be due to “overlap” between two or more phases, we attempted to remove first olivine, requiring least silica, and secondly pyroxene, having the same composition as in the “bulk” (but different proportions), from the residue. In all the four cases the end result is substantial excess of alumina and FeO, ~1 percent and 0.5 to 1.5 percent, respectively, of the total weight. Alkalies show a similar excess in all cases while calcium appears to be deficient in all but Andura. This calcium deficiency is probably not real but is due to uncertainty in the analysis of the Ca-rich pyroxenes.

Iron and magnesium, as might be expected, are about the same in bulk silicates and residue, again excepting Andura for which the results are distorted because of the oxidation discussed previously. This supports the probability that most of the finegrained “matrix” is indeed “rock flour” similar in composition to the bulk meteorites. The excess iron may possibly be explained as admixed ultra-fine metal and/or troilite. The excess of alumina and alkalies, however, is more puzzling. Three possible interpretations are offered: (1) Our modal and phase analyses are too inaccurate to allow these kinds of calculations. The consistency of the results, however, speaks against this, as well as the fact that if olivine is underestimated and pyroxene overestimated in the mode, which seems most likely, the discrepancies become worse. (2) A small amount of an undiscovered discreet phase(s) is present, e.g., corundum or spinel for alumina, or some silicate

TABLE 4.—Chemical composition of bulk silicates from chemical analyses and of unidentified fractions residue in the modal analyses

strongly enriched in alumina and alkalies and possibly iron. Our studies have not so far revealed any such exotic minerals though we have searched for all the ones recently described by Ramdohr (1973) and Mason (1972). (3) The fine-grained ground mass does contain a “real matrix” entirely different from the bulk meteorite. This is in accordance with suggestions by Fredriksson and Keil (1964) that some carbonaceous chondrites are mixtures of low and high temperature fractions. Similar mixture models have been pursued in great detail by the Chicago group led by E. Anders in a number of papers, e.g., Anders (1964) and Laul, et al. (1973); (this paper has numerous references), for especially gas-rich and/or unequilibrated chondrites. A study of carbon distribution in some chondrites (Fredriksson and Nelen, 1969) led to the conclusion that also ordinary equilibrated chondrites may have small amounts of a low temperature real matrix and current work (Fredriksson, et al., in prep.) indicates that this matrix is also enriched in some heavy volatiles, e.g., Pb, Zn, and possibly also N and F (Kerridge, pers. comm.). From our present study, however, we can only conclude that if such a matrix is present, its bulk chemistry is still uncertain although Al/Si, Na/Si, and probably Fe/Si are higher than in the bulk silicates of H-group chondrites (as in some carbonaceous chondrites).

The Pulsora Anomaly

It has been demonstrated that Pulsora is chemically and mineralogically almost identical to three other ordinary equilibrated chondrites although its petrographic grade (Van Schmus and Wood, 1967), even on cursory inspection, seems somewhat lower, i.e., 4–5, than the others of 5–6. Detailed studies of a number of thin sections, however, have revealed several unusual lithic fragments that are not conspicuous in hand specimens. Two of these, extremely different from each other and from the bulk, are described in some detail because they have profound implications as to the thermal history of Pulsora and by analogy of other H-group chondrites. The achondritic fragment (Figure 5) referred to previously consists of relatively coarse, equi-

FIGURE 5.—Crystalline “achondritic” (H7?) fragment, lower right quarter, in Pulsora. Diopside (D), plagioclase (P) and whitlockite occur as large clear crystals together with normal olivine and orthopyroxene. Note the scarcity of metal and troilite (black) as compared to the main mass. Length of section 4 mm.

TABLE 5.—Phase compositions in Pulsora achondritic fragments

Constituent

Olivine

Pyroxene 1

Pyroxene 2

Plagioclase

SiO_2

−

−

−

−

TiO_2

−

−

−

−

Al_2O_3

−

−

1.6

−

FeO

18.0

10.8

5.2

−

MgO

40.5

28.8

17.9

−

CaO

−

2.2

19.0

1.6

Na_2O

−

−

−

−

K_2O

−

−

−

−

granular (in strong contrast with the bulk) olivine, ortho-pyroxene, diopside, plagioclase and apatite, in order of decreasing abundance. The composition of the major silicate phases are given in Tables 5 and 6. Although the accuracy of our iron determinations is no better than ±2 percent relative, we believe that we obtained a precision better than ± 0.1 percent FeO in alternate measurements between fragment and matrix and thus established a small difference in olivine composition, i.e., 18.0 (Table 5) in the fragment and 18.3 (Table 1) in the bulk. The ortho-pyroxene in the fragment (Pyroxene 1) has decidedly higher (2.2%, Table 5) CaO content than in the bulk (1.3%, Table 1) indicating a higher temperature of “equilibration,” whereas the plagioclase is somewhat less calcic, An_5–7 versus An_10, in the bulk. In the fragment, troilite and metal are scarce (~0.5%), the latter consisting of about equal amounts of taenite (~45% Ni) and kamacite (~ 5% Ni). In contrast the main mass contains 17 percent metal with only minor amounts of taenite with ~45 percent Ni; its kamacite has ~7 percent Ni. The overall Ni content of the Pulsora metal (Table 2) is 9 percent corresponding to ~95% kamacite and ~5% taenite.

The glassy fragment (Figures 6, 7) consists of euhedral and skeletal crystals of olivine (~65%) displaying normal zoning, in clear glass (~35%) enriched in silica; the composition is given in Table 6. The olivine has somewhat lower average iron content than olivine in the bulk and in other lithic fragments. The variation indicated in Table 6 is mostly due to zoning in the individual crystals, i.e., the cores have almost constant composition with 10–12 percent FeO. The glass is enriched in Si, Al, Ca, and Na and depleted in Mg and Fe. In its overall composition this fragment resembles some glassy chrondrules described from unequilibrated chondrites (e.g., Fredriksson and Reid, 1965) although the iron content of the olivine is unusually high and the glass has > 5 percent normative quartz, also unusual in glassy chondrules. In addition it contains a small, 0.5 mm, metal-sulfide spherule (Figure 8) with ~65 percent kamacite (7.3% Ni), ~35 percent troilite and a eutectic texture. The troilite contains 0.9 percent Ni in sharp contrast to troilite in the main mass of Pulsora, as well as in other ordinary chondrules, which have < 0.05 percent Ni. The texture indicates rapid crystallization and the 0.9 percent Ni content of the troilite would indicate quenching from ~1000° C (Kullerud, 1963) without any appreciable reheating.

This fragment might be a deformed chondrule even if applying the restricted definition proposed by Fredriksson, et al. (1973), but the irregular shape and the fact that other similar but angular fragments were found lead us to believe that it is a

TABLE 6.—Phase compositions in Pulsora glassy fragments

Constituent

Olivine

Glass

Calculated bulk*

ANALYSES

SiO_2

41–39

65

48.5

TiO_2

−

0.4

0.1

Al_2O_3

−

7.8

2.6

FeO

10–15

11.0

12.2

MgO

49–44

6.5

33.7

CaO

−

5.7

1.9

Na_2O

−

2.5

0.8

K_2O

−

0.3

0.1

NORMS

Qtz

5.5

−

C

0.3

−

Or

2.3

0.8

Ab

30.6

11.7

An

40.8

6.3

Wo

−

1.9

En

8.7

21.2

Fs

11.2

5.6

Fo

−

40.5

Fa

−

11.8

Il

0.5

0.2

* Modal analysis gave ~⅔ olivine and ~⅓ glass of the composition indicated in the two preceding columns. Compare bulk silicates in Table 4.

FIGURE 6.—Thin section of Pulsora including a lithic fragment consisting of olivine in a silica-rich glass (outlined by black, dotted line). Compare Figure 7. The black sphere consists of metal and troilite; see Figure 8. Length of section 11 mm.

fragment of a pre-existing rock. In Table 6 we also present the calculated bulk composition of the silicate in this glassy fragment. It is remarkably similar to the composition of the Pulsora bulk silicates as given in Table 4, again indicating a common parent material.

Clearly, the glassy fragments have not been equilibrated within themselves or with the rest of Pulsora either before or after incorporation in the meteorite. The achondritic fragment might have been equilibrated or recrystallized and drained of metal before incorporation in the bulk which then, if metamorphic equilibration is invoked, must have been metamorphosed somewhere else, then broken up and reassembled together with its fragments, most of which have identical olivine and pyroxene composition. Pulsora, or at least its main mass, must have been “metamorphosed” to exactly the same degree as the higher grade Andura, Butsura, and Sitathali, since their chemistry and mineralogy are essentially identical, implying recrystallization at various temperatures and/or length of time without any differentiation. This seems incomprehensible and to explain the chemical similarities between our four chondrites as well as their textural differences it seems necessary to have (1) a common parent material, (2) heating and cooling rapid enough to retain olivine in silica-rich glass and to

FIGURE 7.—Detail of Figure 6. Skeletal to euhedral zoned olivine (Fa_13, center to Fa_16, margin) in clear, quartz-normative glass. The bulk composition equals that of the silicates in Pulsora. Length of section 0.9 mm.

prevent chemical differentiation (except for draining of metal), and (3) repetitious brecciation and/or recrystallization processes which again do not cause gross chemical changes and consequently no equilibration.

FIGURE 8.—Metal (kamacite, 7% Ni) and troilite spherule in the glassy fragment shown in Figures 6 and 7. The eutectic texture and high (0.9%) Ni content in the troilite indicate quenching from about 1000° C. Diameter 0.5 mm.

Conclusion

We have demonstrated that the Pulsora chondrite, in spite of its constant olivine-pyroxene composition, has never been exposed to thermal metamorphism after agglomeration as has been suggested for most chondrites (e.g., Merrill, 1921; Van Schmus and Wood, 1967; Dodd, 1969). Still, Pulsora, including its greatly variable (H3 to H7) lithic fragments, is practically identical, both chemically and with regard to major phase (and possible matrix) composition, to Andura, Butsura, and Sitathali. These latter three stones may seem to be of a higher average petrographic grade but they do contain, as might be perceived from Figures 1–4, more fine-grained parts similar to the main mass of Pulsora (while Pulsora has high grade fragments). Thus, by analogy, we contend that there is no compelling evidence for the assumption that the three other chondrites here described, or any other ordinary chondrite, ever suffered severe, long term thermal metamorphism, or that the constant olivine-pyroxene compositions were established by such processes. Rather, it seems that rapid, multiple processes acting on a common (at least chemically) parent material may create conditions under which olivine-pyroxene may retain their constant initial composition once established by subliquidus, or even subsolidus, crystallization (Fredriksson, 1963; Kurat, 1967; Blander, et al., 1970). Impacts on moderate sized bodies, > 10^2 to ~ 10^3 km, seem to be the most plausible and currently most accepted explanation for the contradictions presented by ordinary chondrites. Recent investigations of lunar impact breccias, glasses, and chondrules and the interpretation thereof also seem to corroborate the impact origin of chondrites (Fredriksson, et al., 1973).

Appendix

MODAL ANALYSIS WITH THE ELECTRON PROBE

Like most chondrites the four stones investigated in this study are fine grained and the minerals are intricately intergrown. Thus modal analysis by point counting under the microscope is practically impossible as illustrated in Figures 1–4 and especially in the frontispiece. The proportions of metal, troilite (some oxides) and silicates can be readily estimated (e.g., Keil, 1962) but even estimates of

TABLE 7.—Identification of phases by number of total counts

FeKα

CaKα

MgKα

Phase

>

<

>

<

>

<

1 Kamacite

21000

99000

50

500

20

500

2 Taenite

15000

21000

200

500

20

500

3 Troilite

15800

17500

100

200

20

500

4 Olivine

2500

5000

50

150

4500

10000

5 Pyroxene-1

1500

3000

150

600

1500

5000

6 Pyroxene-2

500

3000

600

10000

1300

5000

7 Plagioclase

20

500

500

1500

20

300

8 Apatite

20

400

10000

25000

20

1000

9 “Others” or no fit

−

−

−

−

−

−

Note: Taenite is distinguished from troilite by the CaKα count, i.e., the background, the difference (somewhat uncertain) being caused by the different average atomic number (this adds another variable). In some cases “Taenite 2” was substituted for apatite by changing the criteria for Phase 8 to Fe, >10000 and <15000; Ca. (i.e., background) >200 and <500; and Mg >20 and <500.

the ratio of olivine to pyroxene in Andura (relatively coarse) differed by more than 50 percent between two of us and the amount of residue (unidentified) varied from 18 to 30 percent. In a study of Forest Vale (Noonan, et al., 1972) more rigorous optical criteria were applied which resulted in better olivine/pyroxene ratios but left ~ 45 percent of the points (i.e., > 50% of the silicates) unidentified. We, therefore, decided to resort to point counting by electron probe, simultaneously registering the relative abundance of three elements. Similar techniques have been used before (e.g., Keil, 1962, 1967), but we believe that the procedure used for this study warrants a brief description for three reasons: (1) to illustrate the accuracy (or lack) of some of our calculations, (2) some of the modifications appear to be new and easily adapted to other systems that include computerized data reduction, and (3) the inherent possibility to identify ultrafine interstitial or intergrown minerals, especially if relative abundances of six or more elements are determined simultaneously, as is possible with various modern instruments.

In our study we used an ARL EMX instrument run at 20 kV, and ~ 0.25μA beam (~0.025μA sample) current. The three spectrometers were tuned to Fekα, Cakα and Mgkα and intensities recorded in silicate standards were approximately 125 cps (counts per second) per 1 percent Fe, 220 cps/1 percent Ca and 115 cps/1 percent Mg. Counting time was 2 seconds per point and the sample was moved mechanically (manually) under the beam on a 0.3 × 0.3 mm grid during the print out (typewriter and punch cards) time of ~ 3 seconds; thus each point required an average of ~ 6 seconds and a typical thin section ~ 1 cm^2 was analyzed within 1½ hours. No real concentrations were estimated. Rather, phases were identified by number of total counts as established for each run as illustrated in Table 7. Similarly any other phases can be introduced and of course any suitable elements can be substituted for Fe, Ca, Mg to characterize these phases. The developed computer program readily accommodates such changes, i.e., it accommodates eight “fixed” phases, one “unknown” (frequently caused by overlap of different phases) and one “reject,” i.e., if all three channels register background or less, the point is not counted but the number of such points is registered and might in special cases be used to identify a special “phase,” e.g., holes or pores in a sample, etc. If the counts for each of the three channels are registered on punch card only, the limits as exemplified in the table have to be added, i.e., 48 digit (up to 10^7 counts per channel!) numbers which can be accommodated on 5 IBM cards. (A print out of the current program in Fortran IV is available on request.) The program at present is designed to accomodate up to 750 points, which we consider more than adequate for most thin sections. An average run on a Honeywell 1250 takes a maximum of 2 minutes.

In the near future an electron probe capable of registering simultaneously nine elements will be available. This will make it possible to define more sharply a greater number of phases, but this may not lead to a much greater resolution of phases in fine-grained rocks, especially those with a glassy or crypto-crystalline matrix. It should, however, be possible to obtain the average composition of such a fine-grained matrix and/or apportion (i.e., calculate the norm) unidentified points among the major phases, leaving only small amounts of excess elements or compounds.

Literature Cited

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1964. The Iron, Magnesium, Calcium and Nickel Distribution in the Murray Carbonaceous Chondrite. Meteoritics, 2:201–217.

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Impact Survival Conditions for Very Large Meteorites, with Special Reference to the Legendary Chinguetti Meteorite

Robert F. Fudali and Dean R. Chapman

ABSTRACT

Contrary to popular belief, very large meteorites (>> 1000 tons) can be sufficiently slowed by aerodynamic drag to survive impact with the earth’s surface provided that they enter the atmosphere at very low angles. This is a stringent requirement and survival probabilities for large, unguided objects are low; but they are not zero. Based on high-velocity impact experiments and published tabulations of the parameters of shallow angle entry trajectories, we estimate the probability of survival for an iron meteorite approximately the size and shape of the legendary Chinguetti meteorite (100 meters × 40 meters × 20–40 meters) to be between 0.1 and 1 percent. Together with a limiting estimate of the flux of such bodies encountering the earth, this leads to an expected survival rate of one per 10^8—10^9 years on the earth’s land surface.

Robert F. Fudali, Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, D. C. 20560. Dean R. Chapman, Thermo- and Gas-Dynamics Division, NASA Ames Research Center, Moffett Field, California 94035.

Introduction

In 1916, a small (4.5 kg) meteorite was found in the Adrar region of Mauritania (then French West Africa) by a captain in the French army, Gaston Ripert. It was designated the Chinguetti Meteorite, after the nearby oasis of Chinguetti (20° 28’N, 12° 20’W). The meteorite presently resides in the Muséum National d’Histoire Naturelle (Paris).

The fascinating part of the story is that Ripert claimed the meteorite was but the tiniest part of a gigantic mass that he was led to, with the greatest reluctance, by the then chieftain of Chinguetti, Sidi Ahmed Ould Zein. Following is Ripert’s description of the find (as originally transcribed by Lacroix, 1924, and cited in Monrod, 1952):

This specimen was collected about 45 km. to the southwest of Chinguetti and to the west of Aouinet N’Cher. It was lying on top of an enormous metallic mass measuring about 100 m. on one side and about 40 m. in height, which stands up in the middle of dunes covered by a desert plant called ’sba’ [sic]. (The mass) is in the form of a compact, unfractured parallelepiped. The visible surface is vertical, standing like a cliff above the sand, which, driven by the wind, has grooved its base to such an extent that its upper edge overhangs; the part worn by eolian erosion is polished like a mirror. The sand has piled up against the opposite face and hides it entirely, a fact that made it impossible to estimate its third dimension. The upper surface of the mass bristles with little needles, which the Arabs have tried to remove; but, because of the malleability of the metal, these were only bent. Some less important blocks (of the same material) are scattered about the neighborhood.

Understandably, this report caused considerable excitement in 1924. If the meteorite existed it would be of enormous mass. Based on dynamical considerations to fix the unreported third dimension we estimate a minimum mass of 500,000 tons and a more likely mass in excess of 1,000,000 tons. Since it would have had to tumble and skid to rest from a high velocity, the most stable attitude was probably achieved during the final stages of deceleration and this would be with the smallest dimension vertical. In the event that the vertical dimension is instead the intermediate dimension it is highly unlikely that the unknown horizontal dimension could be significantly smaller than the vertical dimension. We therefore assume that the unknown dimension would be at least 20 meters and more likely in excess of 40 meters.

In addition to the scientific interest, the meteorite would be large enough to generate thoughts of commercial gain. Over the next 14 years there were several, more or less random, attempts made to relocate the original site, without success. Curiously, it was not until 1932 that Ripert was contacted for help in these endeavors and, by then, he apparently retained only a vague notion of the general area of the site. Further, his guide had long since died. In reviewing the problem, Monod (1952) reproduced parts of two letters written by Ripert at about this time. In 1932 Ripert (translated by Brady) wrote, in part, to Dr. Jean Bosler, Director of Le Verrier Observatory in Marseille:

Unfortunately, 16 years have passed since I had occasion to describe the existence of this meteorite. The times were such that everything else was blotted out by the dramatic events that were occurring in France, and I could not realize at the time all the interest that this meteorite might arouse. I spoke of it incidentally, when I was leaving Mauritania, to one of my friends, M. H. Hubert, a Doctor of Science at Dakar, who did not seem to attach any great importance to its existence.

Moreover, in order to satisfy the urgent demands of my guide I had taken with me neither compass nor any material that would permit me to make notes or any measurements whatsoever; also, I could remain only a very short time, because of the guide’s haste to leave the spot; so my observations were extremely cursory. I was able to state that the meteorite formed a sort of cliff, with numerous projecting ridges of sand, lying in an approximately southwest direction, while the northeast side was completely covered by sand. I found there a small fragment, well rounded at the edges, which I turned over to M. Hubert. On one corner (of the large mass), toward the west, I think, sand had carved out fairly thick metallic needles, which I could not loosen or remove. Of the metallic nature of the large mass there could be no doubt at all. Examination of the small specimen given to M. Hubert proves this fact. I tried to detach one of the aforesaid needles by pounding it with the small heavy lump (= the small meteorite). The specimen showed at every point of contact traces of hammer marks, the same condition being true of the needles; and, finally, the surface appearance of the large mass was in no way comparable to that of the blackish polished surface of the rocks that are found on the ’reg’ and on the sandstone plateaus of the Adrar. On my return, I wrote down my observations (based on my memory, which was very good at the time), but, since then, I have moved so much from place to place that I do not know where I put those notes. In any case, I told M. Hubert everything that I had seen which was then quite clear in my mind.

As you may imagine, this meteorite, half-covered by sand in 1916, is very likely completely covered now, but, even so, I am astonished that it has not been found by the civilian and military expeditions that have been sent out since 1929 to look for it. It seems likely that they have been blocked by a conspiracy on the part of the natives, who seem anything but anxious that its existence should be known to Europeans. I realized this (fact) when I overheard a conversation among the camel drivers when I was with the Adrar camel corps. I had spoken of (the meteorite) to the head man of Chinguetti, Sidi Ahmed Zein, who at first vigorously denied its existence, and it was only after long conversations (negotiations?) that he consented, in spite of his fears, to lead me secretly to the spot, on condition that I would take nothing with me that might permit me to describe the exact position of the meteorite, or to make notes. Sidi Ahmed died, apparently of poison; and, without wishing to establish any connection between the facts, I cannot now point out anyone who could serve as a guide.

And in 1934 he wrote, in part, to Monod (1952; translated by Brady):

I know that the general opinion is that the stone (rock) does not exist: that, to some, I am purely and simply an imposter who picked up a metallic specimen on the ’reg’ of Mauritania; that, to others, I am a simpleton who mistook an exposure of sandstone, blackened and polished as is so often the case in that country, for an enormous meteorite. I shall do nothing to undeceive them. I care very little for what any of them may think. I know only what I saw, because I saw it, and I could probably have found (the mass) again if I had been directed to do so, when my visual memory and my age still permitted.

Monod in 1934, and one A. Pourquie, in 1938, conducted search expeditions into the Chinguetti region—both with negative results (Monod, 1952). At that point World War II intervened and the matter was not seriously broached again until the early 1950s. In his 1952 paper Monod was still convinced the huge meteorite could very well exist. However, based on his extensive experience in the region, he cautioned:

Let me add that if the meteorite is actually located among the dunes of Ouarane, 10 hours to the southeast[1] of Chinguetti, the very nature of this terrain is unsuited to easy exploration. It is foolish, of course, to pursue a search (for the meteorite) in a random fashion merely in the hope of making a lucky discovery.

Thus far, this point has been academic as there have been no further efforts to relocate the site. The reason for this neglect is that it is widely believed to be physically impossible for such an enormous mass to survive an impact with the earth’s surface. This belief is based on simple aerodynamic calculations, which have been generally interpreted as precluding any significant atmospheric braking if the incoming meteoritic mass exceeds a maximum of 100 to 1000 tons. This has been uniformly asserted in several meteoritic texts that have enjoyed wide circulation (e.g., Mason 1962; Hawkins, 1964; Heidi, 1964; Wood, 1968).

With little or no atmospheric braking a meteorite impacts the earth’s surface with enough kinetic energy to destroy both itself and a significant portion of the target rock. And there surely is ample evidence—in the form of a number of meteorite impact craters of modest dimensions—that meteorites of mass far less than that estimated for Chinguetti do normally explode upon encountering the earth’s surface. But what is not generally appreciated is that this is a normal, rather than an inevitable, result. In this paper we demonstrate that, under special conditions, a Chinguetti-size meteorite could survive a terrestrial impact essentially intact. In the following sections we delineate the conditions necessary for the survival of such a meteorite, and we compute the approximate probability of encountering such conditions. As one might suspect, the conditions are stringent and the concomittant probabilities are small—but they are certainly not zero.

TABLE 1.—Fate of aluminum projectiles impacting sand targets at high velocities and low incident angles (NASA Ames Light-Gas Gun Range experiments)

Round

Vt (km/sec)

Γ_4

Γ_4

Fate of projectile

(degrees)

DLG

209

6.1

2.1

0.9

Essentially intact

211

6.5

4.75

1.1

Two main fragments

221

5.7

7.33

1.15

Three main fragments

215

6.3

15

−

Fragmented into small pieces

233

5.9

30

−

Fragmented into small pieces

VGP

788

1.9

2.1

1.5

Intact

791

1.8

4.75

3.6

Intact

792

1.9

7.33

2.85

Intact

796

1.8

15

1.32

Essentially intact

TABLE 2.—Variation of the effective strength of aluminum projectiles as a function of their diameter (NASA Ames Light-Gas Gun Range experiments)

Projectile diameter (inch)

Impact velocity for same degree of deformation (km/sec)

Corresponding energy for same degree of deformation (ergs)

1/16

0.8

2×10^7

1/4

1.1

2×10^9

1/2

1.2

2×10^10

The foregoing should in no sense be considered an endorsement for the existence of the legendary Chinguetti meteorite. The primary purposes of this paper is not to demonstrate that it does exist, but that such a large meteorite can exist. Clearly this is the absolute minimal requirement necessary if a systematic search for the meteorite is ever seriously contemplated.

ACKNOWLEDGMENTS.—Donald Gault and John Wedekind of the NASA Ames Research Center generously furnished us with the unpublished, experimental high-velocity impact data vital to our study. For this, and for a number of stimulating discussions on all aspects of the study, we express our deep appreciation. We also thank Lionel Levy of the NASA Ames Research Center for the computer-generated trajectories of a large iron meteorite subsequent to ricochet at the earth’s surface.

Experimental Data on Impact Survival

There is, of course, no possibility of slowing a Chinguetti-size meteorite to terminal velocity by atmospheric braking alone. In the following section we show that the minimum possible velocity such a body could have upon impact would be 3–4 km/sec, and higher velocities are much more probable. We must therefore consider the possibility of survival only for impact velocities of 3 km/sec and higher.

Some of the hypervelocity impact experiments done at the light-gas gun range of NASA Ames Research Center have a direct bearing on this problem. Most of these impact experiments have been characterized by high angles of impact (> 30°). But the few experiments carried out at low incident angles show that, for aluminum projectiles impacting sand targets at velocities between approximately 2 and 6 km/sec, the fate of the projectile is a function

FIGURE 1.—Relationship between impact angle Γi, impact velocity Vimp, and rebound angle Γr. Aluminum projectiles into sand targets.

of both velocity and incident angle. For a given velocity, as the incident angle is lowered, a value is reached below which the projectile will ricochet intact. The pertinent experimental data are shown in Table 1. Figure 1 plots the angle of ricochet against the angle of incidence for three impact velocities. Note that in all cases the ricochet angle is significantly less than the incident angle.

We have used the data in Table 1 to approximately fix the boundary separating the fragmentation domain from the domain of intact ricochet on plots of impact velocities versus incident angles in Figures 2 and 3. Admittedly the data are scanty and

FIGURE 2.—Possible earth impact conditions for shallow angle entry trajectories of an iron meteorite with .

there is a rather large uncertainty associated with this boundary placement, especially at higher velocities. However, it seems likely that the boundary, as drawn, is conservative. For a Chinguetti-size, nickel-iron meteorite the true boundary should lie somewhere to the right of the boundary shown in Figures 2 and 3. There are two reasons for this: (1) Nickel-iron has a much greater strength than aluminum, and (2) scaling up from the tiny experimental projectiles to a large meteorite should be favorable for impact survival. Although the shock wave strengths are independent of scale, the deceleration or body forces acting on each element of the projectile vary inversely with the scale of the projectile. We therefore expect a large projectile to

FIGURE 3.—Possible earth impact conditions for shallow angle entry trajectories of an iron meteorite with .

effectively behave as if it were stronger than a small projectile. Some experimental confirmation of this expectation is shown in Table 2.

The conditions a projectile experiences subsequent to ricochet are specifically discussed in the following section. Here we merely point out that nothing subsequent to the initial impact can begin to approach this initial event in potential destruc-tiveness. This is because the projectile loses energy during ricochet, and is subject to further atmospheric braking after ricochet.

Possible Impact Conditions

Some years ago, Chapman (1959, 1960) published an analytical method for studying the motion of extraterrestrial bodies on shallow entry trajectories into the earth’s atmosphere. So that these trajectory calculations could be generally applied to any planetary atmosphere and to incoming bodies with any physical properties, the trajectories were described in terms of two dimensionless functions. The conic perigee parameter Fp delineates the conditions at the perigee point of the hypothetical conic trajectory that the incoming body would have had if there were no planetary atmosphere. It characterizes the trajectory prior to atmospheric encounter and is defined as

The trajectory through the atmosphere is characterized by a dependent variable termed the Z function:

where, for both equations ρ = air density, r=radius from the planet’s center, β = the atmospheric density decay parameter, M = mass (grams) of the incoming body, A = cross-sectional area normal to the flight path (cm^2), CD = the atmospheric drag coefficient, ū = the ratio of the horizontal velocity component at any point along the flight path to the circular orbital velocity (8 km/sec), and subscript p refers to conditions at the conic perigee.

For an incoming body of given Fp, initial velocity, and lift force to drag force ratio (L/D), Z can be determined at all points on its atmospheric trajectory. If Z is known, a number of other pertinent entry motion parameters can be calculated, including the horizontal velocity component and the trajectory angle with respect to the local horizontal. This has been done for a large number of trajectories and the results are assembled in computer-generated tables (Chapman and Kapphahn, 1961). One such table is reproduced herein for illustrative purposes (Table 3).

In order to use these tables for the problem under consideration, we begin by determining Z/ū at sea level (i.e., at impact) for Chinguetti-size meteorites, using equation 2. This quantity is conveniently given if we use the density of air at set level, ρ_0, for the calculation. For purposes of these calculations the following assumptions and approximations are made: (1) The meteorite is oriented by aerodynamic forces such that the minimum dimension is

TABLE 3.—Atmospheric behavior of an object entering the earth’s atmosphere under the following initial conditions: Initial velocity = 13 km/sec, Lift/drag = 0, Conic perigee parameter Fp = 0.466, and Initial atm. encounter angle= −5.00° (modified from Chapman and Kapphahn, 1961:155)

parallel to the flight path. The calculations are carried out for two minimum dimensions, 20 meters and 40 meters. (2) Density of the nickel-iron meteorite is 8 gm/cc. (3) The meteorite has no aerodynamic lift, either positive or negative (i.e., ballistic entry). The lift-to-drag ratio (L/D) is therefore zero. (4) The drag coefficient CD ≈ 1.5 over the entire flight path. (5) The variation of atmospheric density with height is exponential and everywhere in the earth’s atmosphere. (6) r ≈ radius of the earth = 6 × 10^8 cm. (7) For shallow angle entries, the (normalized) horizontal velocity component, ū, approximately equals the meteorite’s entire velocity.

Now M/A = gm/cm^2, where is the average depth of the meteorites (in cm) in the direction parallel to the flight path. Therefore M/CDA = 5.3 gm/cm^2. Also ρ_0 = 0.0012 gm/cm^3. Substituting in equation (2) we have:

Table 3 displays the trajectory parameters of a body with zero lift, entering the earth’s atmosphere at an initial velocity of 13 km/sec and an initial angle of —5.00° (the negative sign merely denoting that the body is descending). From this table we see that a meteorite characterized by (Z/ū)o = 0.57 would impact the earth’s surface at a velocity of 7.4 km/sec and an angle of —1.65°, 75 seconds after first encountering the atmosphere. If (Z/ū)o=1.14, the meteorite would impact at 4.4 km/sec and −2.8°, 96 seconds after first encountering the atmosphere. It might at first seem paradoxical that the impact angle can be less than the initial entry angle since the trajectory must always steepen (in an absolute sense) due to the combined effects of gravity and aerodynamic deceleration. However, this may indeed be the case for an impact angle measured with respect to the local horizontal since the earth’s surface curves away from the trajectory path. Both sets of parameters define points within the intact ricochet domain as delineated in Figures 2 and 3. Using the complete tables of Chapman and Kapphahn (1961),

TABLE 4.—Computer-generated trajectory parameters and conditions at second impact for an iron meteorite of meters ricocheting with velocities V_1and angle Γ_1

V_1(km/sec)

Γ_1(degrees)

Range (km)

Max. height (km)

V_2 (km/sec)

Γ_2 (degrees)

5.3

1.3

161

1.1

3.9

−1.8

4.5

1.9

153

1.4

3.4

−2.4

4.5

1.5

125

0.9

3.5

−1.9

5.0

1.0

114

0.6

4.0

−1.3

6.0

0.5

106

0.3

4.8

−0.7

6.0

0.8

152

0.6

4.4

−1.1

7.0

0.5

172

0.5

4.9

−0.8

7.0

0.7

211

0.9

4.6

−1.2

8.0

0.4

233

0.7

5.0

−0.9

8.0

0.7

306

1.5

4.5

−1.6

a number of such points can be plotted, generating the family of lines shown in Figures 2 and 3. Each line contains all the impact velocities and angles (of interest here) for a single initial encounter velocity. Lines corresponding to encounter velocities of 11.2, 13, 16, and 20 km/sec are plotted. An encounter velocity of 11.2 km/sec (escape velocity) is, of course, the lower limit for an incoming meteorite and we consider velocities between 13 and 16 km/sec to be the most likely range for large iron meteorites. Clearly, at least for all encounter velocities less than 20 km/sec, a significant portion of the generated lines lie in the intact ricochet domain.

For all impact velocities below about 8 km/sec, the associated impact angle is less than ~5° for a meteorite of and less than ~4° for a meteorite of . Combining these data, with those shown in Figure 1, we see that the only possible rebound angles are less than 3° and most are less than 2°. We have used these rebound angles to compute the after-ricochet trajectories of a meteorite of , and the conditions at second impact. The computer-generated results are shown in Table 4. In all cases there is a significant reduction in velocity at second impact and, in every case but one, the second impact angle is less than 2°. The velocities at second impact would actually be somewhat less than those shown since we did not consider any energy (and velocity) loss due to the initial impact and ricochet. Atmospheric deceleration after rebound is most effective for the higher velocity projectiles, so there is not a great deal of difference between the velocities and angles of the various cases at second impact—velocities varying from 3.4 to 5.0 km/sec and impact angles from − 0.6° to —2.4°. At these lower velocities and very low incident angles we feel that such a meteorite would most likely tumble and skid to rest without ricocheting a second time. Since aluminum projectiles vertically impacting sand targets at 2.5 km/sec remain essentially intact (although severely deformed), we expect a nickel-iron meteorite to survive such a skid to rest essentially intact.

Probabilities of Impact Survival

If certain pre-atmospheric trajectories will permit the impact survival of a Chinguetti-size meteorite, then there must be an envelope or entry corridor containing these trajectories. An unguided, extraterrestrial body on a collison course with the earth may or may not encounter this corridor. To a first approximation, the probability of a “favorable” encounter is merely the ratio of the cross-sectional area of the annular ring defining the entry corridor to the cross-sectional area of the earth itself:

where Δr is the width of the annular ring and r is the earth’s radius. To be sure, the equation is not precise, nor is it strictly the equation of applicability since the earth’s gravity field creates an effective capture Cross-section and an annular entry corridor both of which are larger than the comparable terms in equation (6). A precise derivation, however, is complex and, considering the approximations and assumptions already made, the increase in precision would be meaningless. The first approximation is at worst within a factor of 2 of a more precise derivation—for a meteorite with the lowest possible geocentric velocity (11.2 km/sec). The approximation improves as geocentric velocities increase.

For an exponential atmosphere, Δr between any two pre-atmospheric trajectories can be determined from the ratio of their conic perigee parameters since these parameters vary directly with air density (equation 1). The atmospheric density changes by a factor of 10 for every 16 km change in altitude and the corridor width is simply:

The upper limit to any entry corridor will be a trajectory resulting in just enough atmospheric braking to transfer the incoming body to an unstable elliptical orbit, which will decay and lead to atmospheric entry on a subsequent pass. For all practical purposes this atmospheric entry will be identical to that for a body with circular satellite velocity, regardless of the initial encounter velocity. (Thus all the curves in Figures 2 and 3 degenerate to the same point). Beyond this limiting trajectory the incoming body will swing around the earth on a nonreturn hyperbolic trajectory. The nonreturn boundaries for zero-lift bodies with initial velocities of 13 and 16 km/sec are characterized by Fp’s of 0.036 and 0.10, respectively (Chapman, 1960, fig. 14). The lower corridor boundary can be any arbitrarily chosen trajectory whatsoever. For example, Table 3 describes the atmospheric behavior of incoming bodies with initial velocities of 13 km/sec and pre-atmospheric trajectories characterized by Fp = 0.466. The ratio 0.466/0.036 = 12.9 = 101.11, so

The concomitant, approximate probability of an unguided, incoming body (with initial velocity of 13 km/sec) encountering this corridor is

This probability can be related to survival as follows: In Figure 3, the 13 km/sec curve encompasses possible impact velocities and angles for a meteorite of . Table 3 was used to generate one point on that line—the point labeled.006. For that class of meteorites encountering the earth, characterized by and Vi=13 km/sec, 0.6 percent will impact at velocities and angles given by the segment of the 13 km/sec curve lying between the .006 point and the atmospheric braking point. All the other numbered points in Figures 2 and 3 were derived in the same way and have the same meaning.

Discussion and Conclusions

From the foregoing sections it should be clear that meteoritic masses very much greater than 1000 tons can survive a terrestrial impact under certain conditions. In fact, mass is not strictly the governing parameter and a meteorite even more massive than the specific Chinguetti-size bodies considered herein could also survive a terrestrial impact, provided the critical parameter—its linear dimension parallel to the atmospheric flight path—remains modest. The probability of survival, however, will decrease with increasing mass because of the need for a meteorite to assume a favorable flight attitude in the atmosphere. If a meteorite has a stable flight attitude, it will be with the minimum dimension oriented parallel to the flight path. For the present study we have assumed that if all dimensions are small enough to permit significant deceleration by the atmosphere, then the meteorite will become oriented in its stable attitude prior to maximum deceleration. This holds for the maximum dimension considered (100 m) on most shallow-angle entry trajectories. As the other dimensions increase beyond this, the pre-atmospheric orientations that will lead to stable atmospheric orientation are reduced and thus the survival probability decreases, although it never goes to zero as long as the minimum dimension is fixed.

With respect to the specific question of the possible existence of the Chinguetti meteorite, we reiterate the fact that the curves, boundaries and probabilities displayed in Figures 2 and 3 are all approximate. Nevertheless, the data are surely precise enough for order of magnitude conclusions. Bearing this in mind we estimate the survival probability of a Chinguetti-size meteorite (whose geocentric velocity lies somewhere between 11.2 and 20 km/sec) to be between 0.1 and 1 percent. Put another way, such a body has between one chance in 100 and one chance in 1000 of surviving a terrestrial impact. Now, based very crudely on the number of more recent, known and probable terrestrial impact craters due to meteorites with kinetic energies similar to the hypothetical Chinguetti body, the upper limit to the encounter frequency of such bodies with the earth’s land surface cannot exceed one per 10 6 years (over the past few tens of million years). This means that the expected survival (and potentially recoverable) rate can be no higher than one every 10^8 to 10^9 years. Because the complete oxidation (and thus destruction) of large iron meteorites on the earth’s surface is accomplished in a time that is short compared to 100 million years, we are led to the following conclusions. First, the Chinguetti meteorite can exist. Second, from a purely statistical aspect, the odds are heavily against its existence. Of course, the specific existence or nonexistence of the Chinguetti meteorite is not purely a statistical problem, since it involves a reported observation. Thus there are only two possible probabilities: Either the observer, Gaston Ripert, was mistaken (or lied), or his report was correct. In the former case, the probability that the Chinguetti meteorite exists is 0. In the latter case, the probability is 1. No other probability calculations are meaningful, nor is it possible to discriminate between 0 and 1 at this point. The combination of survival and weathering rates, however, does tell us, clearly and irrevocably, that if the Chinguetti meteorite does indeed exist, it must be, now and forever in the history of mankind, unique.

Literature Cited

Chapman, D. R.

1959. An Approximate Analytical Method for Studying Entry into Planetary Atmospheres. NASA Technical Report, R-11: 44 pages.

1960. An Analysis of the Corridor and Guidance Requirements for Supercircular Entry into Planetary Atmospheres. NASA Technical Report, R-55: 47 pages.

Chapman, D. R., and A. K. Kapphahn

1961. Tables of Z Functions for Atmospheric Entry Analysis. NASA Technical Report, R-106: 271 pages.

Hawkins, G. S.

1964. Meteors, Comets and Meteorites. 134 pages. New York: McGraw Hill.

Heidi, F.

1964. Meteorites. 144 pages. Chicago: The University of Chicago Press.

Lacroix, A.

1924. On a New Type of Meteoric Iron Found in the Desert of Adrar in Mauritania. Comptes Rendus, 179:303–313.

Mason, B.

1962. Meteorites. 274 pages. New York: John Wiley and Sons.

Monod, Th.

1952. Le problème de la météorite de Chinguetti. Bulletin de la Direction des Mines, Gouvernement Général de I’Afrique Occidentale Francaise, 15 (2):405–412. [Translated by L. F. Brady, “The Problem of the [French West Africa] Chinguetti Meteorite [CN = 0127,202:]”, and published, in 1955, in Meteoritics, 1 (3):308–314.]

Wood, J. A.

1968. Meteorites and the Origin of Planets. 117 pages. New York: McGraw Hill.

Preliminary Data on Eight Observed-Fall Chondritic Meteorites

Roy S. Clarke, Jr., Eugene Jarosewich, and Albert F. Noonan

ABSTRACT

Eight observed-fall meteorites, five olivine-bronzite chondrites and three olivine- hypersthene chondrites, have been chemically analyzed and assigned a Van Schmus-Wood petrographic classification. The names, dates of fall, and classification of the meteorites are as follows; Ankober, 7 July 1942, H4; Schenectady, 12 April 1968, H4; Dwaleni, 12 October 1970, H4 dark fraction and H6 light fraction; Kiffa, 23 October 1970, H5; Kabo (Gwarzo), 25 April 1971, H4 dark fraction and H5 light fraction; Tathlith, 5 October 1967, L6; Malakal, 9–15 August 1970, L5; Wethersfield, 8 April 1971, L6.

Roy S. Clarke, Jr., Eugene Jarosewich, and Albert F. Noonan, Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20560.

Introduction

During the past several years we have obtained a number of newly fallen chondritic meteorites. These specimens, or samples from them, have been made available as promptly as possible to investigators engaged in time-dependent studies. Distribution of samples for other purposes has also been made, depending upon availability of specimen material. In an effort to support these outside studies, as well as to fulfill our curatorial responsibilities, we have undertaken preliminary examinations of each meteorite. Typically, this includes obtaining as much information as possible about the circumstances of fall and recovery of the meteorite, performing a bulk chemical analysis, a preliminary petrographic examination, and an electron micro-probe examination of the major minerals. Our objective is sound classification, and the data is circulated promptly to those who have need for it. This paper summarizes data on eight observed-fall chondrites.

The meteorites studied are listed by date of fall in Table 1, together with their geographic location, date and time of fall, and the weight of material recovered. Bulk chemical analyses and calculated normative mineral compositions are given in Table 2. In Table 2 the meteorites are listed in order of date of fall within the two major classification groups. The first five meteorites, Ankober, Schenectady, Dwaleni, Kiffa, and Kabo are all olivine-bronzite chondrites (H-group meteorites). The last three meteorites, Tathlith, Malakal, and Wethersfield are olivine-hypersthene chondrites (L-group meteorites).

RELATED LITERATURE.—A number of papers have been published giving cosmic-ray exposure ages and rare gas measurements on meteorites from our list of eight. References are given here, with the names of the meteorites studied, for papers that are not mentioned in our discussion: Bogard, et al. (1973), Tathlith, Malakal, Dwaleni, Kiffa, Wethersfield, and Kabo; Cressy (1970), Tathlith; Fireman and Goebel (1970), Ankober; Fireman and Spannagel (1971), Dwaleni; Reynolds, et al. (1971), Dwaleni; Smith and Firemen (1973), Dwaleni, Kabo, Kiffa, Malakal, and Wethersfield; Tobailem and Lalou (1972), Kiffa; Heimann, Parekh, and Herr (1974), Malakal,

ACKNOWLEDGMENTS.—The Smithsonian Institution’s Center for Short-Lived Phenomena has been responsible for obtaining our specimens of the Malakal, Dwaleni, Kiffa, and Kabo meteorites. We are indebted to the Center’s director, Robert A. Citron, and to David Squires for their assistance. Joseph A.

TABLE 1.—Recovery information on eight observed-jail chondrites (listed by date of fall)

Name

Location

Date

Time

Recovered Weight

Ankober, Ethiopia

9°32’N, 39°43’E

7 Jul 42

10:00 a.m. local time

7 kg

Tathlith, Saudi Arabia

19°21’N, 43°44’E (recovery site, both ±3’)

5 Oct 67

5:15–5:30 a.m. local time

~2kg

Schenectady, New York

42°51’39”N, 73°57’1”W

12 Apr 68

8:30 p.m. local time

283 g

Malakal, Sudan

9°30’N, 31°45’E

9–15 Aug 70

Not known

>2 kg

Dwaleni, Swaziland

27°12’S, 31°19’E

12 Oct 70

10:30 hours South African time

3.2 kg

Kiffa, Mauritania

16°35’N, 11°21’W

23 Oct 70

About 2:55 p.m. GMT

~1.5 kg

Wethersfield, Connecticut

41°42’N, 72°39’E

8 Apr 71

2–6 a.m. local time (0700–1100 hrs. GMT)

350 g

Kabo, Nigeria

11°51’N, 8°13’E

25 Apr 71

About 4:30 p.m. local time (15.30 GMT)

>10 kg

Nelen did preliminary electron microprobe examinations on several of these meteorites. A grant from the National Aeronautics and Space Administration provided funds for the purchase of the Ankober and Wethersfield meteorites, and to pay recovery expenses for the Kabo meteorite. Dr. Robert Hutchison, British Museum (Natural History) read the manuscript and provided us with several helpful suggestions.

Meteorite Descriptions

The procedures and techniques used in this study are standard for this type of investigation. Chemical analyses were perfomed following the general procedures described earlier (Jarosewich, 1966). Normative mineral compositions were calculated from the chemical data. Olivine and pyroxene compositions were determined using the electron microprobe. Individual mineral grains were selected, and Fe, Ca, and Mg were determined simultaneously. The number of grains analyzed depended both on the homogeneity of the sample and on their availability in the sections at hand. Olivine compositions are reported as mole percent fayalite (Fa) and pyroxene compositions are mole percent ferrosilite (Fs). A petrographic classification is given for each meteorite following the procedure of Van Schmus and Wood (1967).

In the following sections, brief descriptions of each of the meteorites are given in the order in which they are listed in Table 2.

ANKOBER, BOLEDE, ETHIOPIA

The Ankober meteorite fall of 7 July 1942 was observed and attracted local attention at the time. We first heard of it more than 10 years later, when Professor Guglielmo Sensi (1953) of the Pasteur Institue, Addis Ababa, wrote in behalf of the owner, Ato Assafa Abye. Professor Sensi reported that the meteorite had been incandescent in the air and that it had fallen into a field of whitish clay causing no damage. A more dramatic version of the fall attributed to Ato Assafa Abye reflects the excited state of the local inhabitants: “After having touched the earth, it sank to a depth of about one meter, giving forth steam. The natives of the region dug at the ground to remove it, but it was still burning so much they could not take it immediately. They therefore left it in place, saying that it must be a shell fired by the English.” In early 1954 we received a specimen of the meteorite (USNM 2609) and its identification was confirmed by E. P. Henderson. In 1967 Robert Citron, at that time manager of the Smithsonian Institution Astrophysical Observing Station in Ethiopia, obtained the main mass of the meteorite (USNM 3399). The essentially complete individual stone of 6955 g was subsequently deposited in the meteorite collection in Washington.

TABLE 2.—Analytical data on observed-fall chondrites (values in weight percent unless otherwise indicated; chemical analyses, Eugene Jarosewich; microprobe Fa-Fs determinations, Albert F. Noonan; classifications according to Van Schmus and Wood, 1967)

The stone is blocky in shape and about 90 percent of its surface is covered with fusion crust. Late-stage spalling of fusion crust was restricted to edges and corners where the essentially flat surfaces of the meteorite intersect. The stone appears to have tumbled during flight and there is no obvious anterior surface. One of the main surfaces is markedly less smooth than the other surfaces. This suggests a break-up at an early stage during atmospheric passage and the probability that the Ankober fall produced at least two individuals. The fusion crust is brown in color, probably due to oxidation by atmospheric moisture. It is assumed that the stone has been protected from the weather since shortly after its recovery, but we have no certain information on this prior to our obtaining the specimen.

Freshly cut surfaces of Ankober quickly become brown in color due to limonitic staining. Slices are compact and hard, due largely to the metal forming a continuous structural framework. Under low magnification (× 10) cut and broken surfaces are seen to have a surprisingly open structure. Large numbers of submillimeter size cavities are present, into which chondrules, euhedral crystals, and crystal and chondrule fragments protrude. The meteorite has a very uniform texture with no obvious brecciation or veining.

In thin section Ankober is seen to consist of distinct complete and broken chondrules in a matrix of fine-grained silicates and metallic phases. Chondrules do not normally exceed one millimeter in diameter, but a few unusually large ones up to 6 mm across were observed. Minerals present include olivine, bronzite, clinobronzite, taenite, kamacite, and troilite, with minor amounts of chromite, whitlockite, and copper. Forty microprobe analyses indicated a constant silicate composition of Fa_19 for olivine and Fs_17 for the low-Ca pyroxene. Abundant clinobronzite occurs both in chondrules and matrix, often with devitrified glass. Ankober is classified as an H4 chondrite.

SCHENECTADY, SCHENECTADY COUNTY, NEW YORK

The Schenectady meteorite fall of 12 April 1968 produced an individual stone that was recovered following a widely observed fireball. Details of the fall and recovery have been reported by Fleischer, et al. (1970). These authors also classified the meteorite, presented rare gas data, radioactive-ages and cosmic-ray track information. The meteorite is the property of The Schenectady Museum, Schenectady, New York, and it was loaned to us for study in August of 1969.

The physical characteristics of Schenectady are similar to those described for Ankober. Exposure to moisture from the air and during sawing has resulted in limonitic staining. The fusion crust however, is still black. The stone is compact and hard, but under low magnification (× 10) many small cavities can be seen. The openness of the structure, however, is less than that observed in Ankober. The stone has a uniform texture, free of brecciation or veining.

Chondrules are abundant, distinct, and as large as two millimeters in diameter. They are seen in thin section to be in a relatively coarse-grained matrix. The chondrules are composed of olivine, orthobronzite, minor clinobronzite, and devitrified glass. Forty-five microprobe analyses show the principal silicate minerals to be essentially homogeneous, with an olivine composition of Fa_19 and a pyroxene composition of Fs_17. Other minerals identified were taenite, kamacite, troilite, chromite, whitlockite, and copper. The concentration of copper was unusually high with as many as 20 grains found in one polished section. Schenectady is classified as an H4 chondrite.

DWALENI, SWAZILAND

Loud explosions accompanied the fall of the Dawleni meteorite near the Swaziland-Transvaal border on 12 October 1970. Three essentially completely fusion-crusted individuals were recovered promptly from a 12 km^2 area centering on the location given in Table 1. The individuals weighing 2.37, 0.51, and 0.35 kg were recovered from 15 to 18 cm below ground level in moist soil. We received two pieces of the 0.35 kg stone (156 g and 10 g) on 3 November 1970. This sample material and information on the fall and recovery were sent to us by J. G. Urie, Acting Director, Geological Survey and Mines Department, Mbabane.

The Dwaleni chondrite is a compact rock with a pronounced light-dark structure (Figure 1). The one surface available to us shows approximately equal areas of light and dark material, with thin dark veins penetrating both types. The light-colored areas are of uniform composition, have sharp outline and are tightly bound to the darker material. Bogard, et al. (1973:2429) have noted that the dark fraction of Dwaleni is unusually rich in rare gases.

Both light and dark materials undoubtedly have similar bulk compositions, but minor differences in

FIGURE 1.—The Dwaleni, Swaziland, chondrite. A broken surface showing light-dark structure and veining. One and a half times actual size.

individual mineral compositions between these two materials were noted. The lighter material contains relatively large crystals of homogeneous olivine, bronzite, and plagioclase. Chondrules are absent or indistinct. Twenty-five grain analyses gave olivine, pyroxene, and plagioclase compositions of Fa_20, Fs_17 and An_12. The petrographic classification of this material is H6. The dark material, however, contains olivine and pyroxene of slightly higher magnesium content and of somewhat variable composition. Eighteen grains analyses gave olivine and bronzite compositions of Fa16–19 and Fs_15–18. Chondrules up to one millimeter in diameter are well defined and contain turbid glass. The petrographic classification of the dark material is H4. Kamacite, taenite, troilite and minor chromite, and copper occur in Dwaleni, mostly in the light-colored fraction.

KIFFA, MAURITANIA

At 2:55 p.m. GMT on 23 October 1970, detonations were heard and a smoke cloud observed in the neighborhood of the town of Kiffa. About 10 a.m. the next morning a meteorite specimen was found by a child 8 km southwest of the town. It had made a shallow hole about 20 cm deep in fine sand. The meteorite shattered into many pieces on landing and less than 1.5 kg was recovered. We received a 36 g piece on 17 February 1971 from M. Henri Gruenwald, Chef de Service Géologique, Direction Des Mines et de la Géologie, Nouakchott. M. Gruenwald was also our source of information on the fall and recovery of the meteorite.

The Kiffa meteorite is a friable gray chondrite with distinct chondrules reaching a maximum diameter of approximately 2 mm. The chondrules can be separated with ease from the fine-grained white matrix, which appears to cement the chondrules and metal phases together. The texture is quite uniform and there are no obvious foreign inclusions. Olivine and bronzite are the principal silicate minerals in both chondrules and matrix. Clinobronzite is rare. Twenty microprobe analyses show chondrule olivine and pyroxene to be constant in composition, the fayalite and ferrosilite value being Fa_18 and Fs_16, respectively. The white matrix is composed, at least in part, of what appears to be comminuted chondrules and devitrified glass. In addition to olivine and bronzite, clinobronzite, kamacite, taenite, troilite, chromite, and whitlock-ite were identified. Although chondrules are distinct, Kiffa is classified an H5 chondrite principally on the basis of silicate homogeneity and the presence of only minor clinopyroxene.

KABO, GWARZO DISTRICT, KANO STATE, NIGERIA

The name Gwarzo has been used as a synonym for Kabo.

The Kabo meteorite shower of 25 April 1971 attracted considerable local attention, and at least four stones with a total weight of over 10 kg were recovered. We received a 134 g sample on 9 June 1971. Both the sample and a description of the fall and recovery were provided by Professor M. O. Oyawoye, Geology Department, University of Iba-dan. A detailed description of this meteorite has been prepared by Hutchison and coworkers (Hutchison, et al., 1973).

Kabo is an ordinary chondrite with a subtle light-dark structure. Bogard, et al. (1973) have shown that its dark fraction contains an enrichment of several trapped rare gases. Veining and distorted metal grains in Kabo seem to be preferentially associated with the dark fraction. Chondrules, which range up to two millimeters in diameter in both fractions, are well defined in the dark fraction and less well defined in the light fraction. Clinobronzite occurs in both the light and dark fractions.

The minerals identified in Kabo are olivine, bronzite, clinobronzite, kamacite, taenite, troilite, chromite, ilmenite, whitlockite, chlorapatite, and copper. Thirty grain analyses in the dark fraction show pyroxene variability over the composition range Fs_14–20. The olivines, however, are essentially homogeneous with a composition of Fa_19. Glass occurs as fragments and in chondrules in minor amounts, indicating that the dark fraction is less equilibrated than the light fraction. Thirty olivine and pyroxene grain analyses in the light fraction indicate homogeneous compositions of Fa_19 and Fs_17. The textural and compositional differences result in an H4 classification for the dark fraction and an H5 classification for the light fraction.

TATHLITH, SAUDI ARABIA

The Tathlith meteorite fell early in the morning on 5 October 1967 about 15 km from the village of Tathlith. A single blocky-shaped, fusion-crusted individual was recovered immediately. The exact weight of the stone is not known to us, but estimates based on photographs indicate that it weighed about 2 kg (Figure 2). We received a 205 g slice of Tathlith from Glen F. Brown, Chief, U.S. Geological Survey Field Party, Jiddah, Saudi Arabia on 22 November 1967. It had been identified as a meteorite by Gerhard W. Leo in the U. S. Geological Survey Laboratories in Jiddah. The main mass of the meteorite is believed to be in the possession of the Emir of Abha.

Tathlith is a highly recrystallized gray chondrite of uniform texture. Chondrules range in size up to 3 mm in diameter and are easily discernible on a cut or broken surface. In thin section, however, the chondrules appear relict and intergrown with granular plagioclase and metal. Minerals identified are olivine, hypersthene, clinohypersthene, plagioclase, kamacite, taenite, troilite, chromite, and copper. Twenty grain analyses show the major silicates to be homogeneous with olivine composition of Fa_26 and hypersthene of Fs_21. The plagioclase is also homogeneous with a composition of An_10. Small amounts of clinohypersthene, which are probably

FIGURE 2.—The Tathlith, Saudi Arabia, meteorite, a, Cut surface from which our 205 g specimen was removed. b, Meteorite sitting on cut surface. Scale in inches. Photographs by Gerhard W. Leo, U.S. Geological Survey.

remnant, occur in some of the larger chondrules. Tathlith is an L6 chondrite.

MALAKAL, UPPER NILE PROVINCE, SUDAN

The fall of the Malakal meteorite during the first half of August 1970 into an active military area has been described by Dawoud and Vail (1971). The meteorite fragment that reached Khartoum on 15 August 1970, weighed about 2 kg, and photographs of that piece indicate that it is a part of a considerably larger stone. It is not known if other fragments were recovered. We received a 194 g piece and 4.4 g of fragments from Professor J. R. Vail of the University of Khartoum on 3 November 1970. A comprehensive description of the Malakal meteorite has recently been published by El Rabaa, et al. (1974).

Malakal is a unique meteorite from the point of view of its cosmic-ray history. Cressy and Rancitelli (1974) note that cosmic-ray produced 26Al and 58Mn are anomalously high in Malakal. They conclude that the meteorite must have experienced a two-stage irradiation, and that during the earlier stage Malakal was exposed to a cosmic-ray flux several times larger than that incident on other chondrites or that measured by space probes.

Malakal is a moderately veined and brecciated hypersthene chondrite, with the dark and apparently shock-produced vein material also occurring in patches. Kamacite and troilite also appear to have been partially shock melted. Their interfaces with each other are frequently lacy and diffuse, as are their interfaces with surrounding silicates. Abundant spherules of metal or sulfide are observed within the silicates near the metallic phases. Chondrules are present, ranging up to 5 mm in diameter, and the silicate matrix is moderately recrystallized. The minerals identified are olivine, hypersthene, kamacite, taenite, troilite, ilmenite, chromite, and whitlockite. Twenty grain analyses show the major silicates to be homogeneous with olivine composition of Fa_25 and pyroxene of Fs_21 · Malakal is classified as an L5 chondrite.

WETHERSFIELD, HARTFORD COUNTY, CONNECTICUT

The Wethersfield meteorite fell into the home of Mr. and Mrs. Paul J. Cassarino during the early morning hours of 8 April 1971. It penetrated a roof of asbestos shingles and three-quarter-inch plywood, then passed through four inches of insulating material and nearly went through a half-inch sheetrock ceiling in a second floor room. Debris on the floor of the room called attention to the presence of a 350 g meteorite precariously suspended in the broken ceiling. Richard E. McCrosky of the Smithsonian Astrophysical Observatory, Cambridge, visited the Cassarino’s and obtained the specimen

FIGURE 3.—The Wethersfield, Connecticut, chondrite. The bottom left side of the photograph shows posterior fusion crust and spalled areas of crust. The bottom center area shows a broken surface and extensive interior veining.

for scientific study and preservation. He also canvassed the surrounding area and made numerous inquiries about the possibility of other pieces having been found. Only the one specimen was recovered, and no observations were reported that would allow fixing the time of fall more precisely.

The meteorite as found was largely covered with a dark fusion crust. Areas where the fusion crust had spalled late in flight covered 10 to 15 percent of the surface. The largest single surface covering nearly half of the specimen, was smooth and rounded and appeared to have been a leading surface during atmospheric flight. The other surfaces were more irregular and the opposite surface appears to have been a posterior surface. Its fusion crust is lighter in color, more vesicular, and it has small areas of the darker anterior fusion crust deposited on it. This area of posterior fusion crust is shown in the central area of Figure 3.

Wethersfield is a gray, highly recrystallized chondrite with black veins and patches of black material (Figure 3). This black material appears to have been produced by shock. Relict chondrules range up to 2 mm in diameter, with a few large ones approaching 5 mm. Fifteen microprobe grain analyses show the silicates to be homogeneous, with an olivine composition of Fa_25 and hypersthene of Fs_21 · Other minerals identified were kamacite, taenite, troilite, chromite, and whitlockite. It is classified as an L6 chondrite.

Literature Cited

Bogard, D. D., M. A. Reynolds, and L. A. Simms

1973. Noble Gas Concentrations and Cosmic Ray Exposure Ages of Eight Recently Fallen Chondrites. Geochimica et Cosmochimica Acta, 37:2417–2433.

Cressy, Philip J. Jr.

1970. Multiparameter Analysis of Gamma Radiation from the Barwell, St. Séverin and Tathlith Meteorites. Geochimica et Cosmochimica Acta, 34:771–779.

Cressy, P. J., Jr., and L. A. Rancitelli

1974. The Unique Cosmic-Ray History of the Malakal Chondrite. Earth and Planetary Science Letters, 22: 275–283.

Dawoud, A. S., and J. R. Vail

1971. Malakal Meteorite, Sudan. Nature: Physical Science, 229:212–213.

El Rabaa, S. M., A. M. Daminova, M. I. Dyakonova, L. G. Kvasha, L. K. Levskii, and A. V. Fisenko

1974. The Results of the Investigation of the Malakal Chondrite. Meteoritika, 33:83–89.

Fireman, E. L., and R. Goebel

1970. Argon 37 and Argon 39 in Recently Fallen Meteorites and Cosmic-Ray Variations. Journal of Geophysical Research, 75:2115–2124.

Fireman, Edward L., and Gert Spannagel

1971. Fresh Meteorites in 1970 and the Cosmic-Ray Gradient. Chemie der Erde, 30:83–101.

Fleischer, R. L., E. Lifshin, P. B. Price, R. T. Woods, R. W. Carter, and E. L. Fireman

1970. Schenectady Meteorite. Icarus, 12:402–406.

Heimann, M., P. P. Parekh, and W. Herr

1974. A Comparative Study on 26Al and 53Mn in Eighteen Chondrites. Geochimica et Cosmochimica Acta, 38: 217–234.

Hutchison, R., D. E. Ajakaiye, C. J. Elliott, and F. A. Fry

1973. The Kabo, Nigeria, Meteorite Fall. Mineralogical Magazine, 39:340–345.

Jarosewich, E.

1966. Chemical Analyses of Ten Stony Meteorites. Geochimica et Cosmochimica Acta, 30:1261–1265.

Reynolds, M. A., D. D. Bogard, and C. M. Polo

1971. Dwaleni—A New Gas-Rich Chondrite (Abstract). E.O.S., 52:269.

Sensi, Guglielmo

1953. [Letter from Professor Sensi to the Smithsonian Institution.] Accession file 202751, Office of the Registrar, Smithsonian Institution.

Smith, S., and E. L. Fireman

1973. Ages of Eight Recently Fallen Meteorites. Journal of Geophysical Research, 78:3249–3259.

Tobailem, Jacques, and Claude Lalou

1972. Age d’exposition de la météorite Kiffa. Comptes Rendus des Séances de L’Académie des Sciences, Series B, 274 (21): 1185–1187.

Van Schmus, W. R., and J. A. Wood

1967. A Chemical-Petrologic Classification for the Chondritic Meteorites. Geochimica et Cosmochimica Acta, 31:747–765.

List of Meteorites in the National Museum of Natural History, Smithsonian Institution

Compiled by Brian Mason

ABSTRACT

A brief history of the meteorite collection in the National Museum of Natural History is followed by a list with data of locality, type, and weight of each specimen.

Brian Mason, Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20560.

Introduction

Meteorites formed part of the original collections of the Smithsonian Institution. James Smithson’s bequest, besides the endowment fund, included (Goode, 1897:305) “a cabinet, which… proves to consist of a choice and beautiful collection of minerals, comprising probably eight or ten thousand specimens…. The cabinet also contains a valuable suite of meteoric stones, which appear to be suites of most of the important meteorites which have fallen in Europe during several centuries.” In 1854 the then Secretary, Joseph Henry (1854:18), recorded: “The laboratory of the Institution during the past year has been used by Professor J. Lawrence Smith in the examination of American minerals…. He also made a series of analyses of meteorites, among which were fourteen specimens belonging to the cabinet of James Smithson.” Unfortunately, the specific meteorites from the Smithson collection are not identified, and the meteorite collection was apparently destroyed, along with the rest of Smithson’s cabinet, in the 1865 fire.

In 1880 G. P. Merrill, in a manuscript report, noted only six meteorites in the catalog: Imilac, Vaca Muerta, New Concord, Parnallee, Searsmont, and Cold Bokkeveld. The Tucson iron, which should have formed the chief attraction, was not cataloged, although brought to Washington in 1863. The Casas Grandes iron was also received around 1880, being transferred to the Smithsonian Institution along with much other material from the Philadelphia Centennial Exhibition. However, the collection grew rapidly during the next decade, largely through the efforts of F. W. Clarke, who was appointed honorary curator in 1883. In 1889 he published a catalog of the meteorite collection as of October 1888, in which he lists 128 distinct falls and finds; in addition, there were 217 meteorites in the Shephard collection, which was deposited in the museum by Shephard’s son in 1886 (and ultimately bequeathed to the Smithsonian Institution in 1915). Considerable duplication existed between the two collections, and many of the specimens in both collections were small fragments.

Since that time the meteorite collection has grown steadily. In 1902, W. Tassin brought the Clarke catalog up to date; the Shephard meteorites were listed along with the museum’s collection, and the combined collections contained 348 falls and finds. The most recent published catalog is that by G. P. Merrill, “Handbook and Descriptive Catalogue of the Meteorite Collections in the United States National Museum.” The collection at that time comprised 412 independent falls and finds. In the Annual Report of the Smithsonian Institution, E. P. Henderson (1948) noted that the collection had grown to 767 meteorites.

The present collection contains representative material of some 1300 meteorites, or about two-thirds of all known meteorites. The current catalog in the Department of Mineral Sciences lists over 5700 individual specimens. This collection ranks in size and comprehensiveness with that of the British Museum (Natural History).

ACKNOWLEDGMENTS.—I wish to thank Mr. R. S. Clarke, Jr., and Mr. A. F. Noonan for much assistance in compiling this list, and Dr. W. R. Van Schmus for some unpublished data on the classification of individual chondrites.

Literature Cited

Clarke, F. W.

1889. The Meteorite Collection of the U.S. National Museum: A Catalogue of Meteorites Represented November 1, 1886. Report of the Smithsonian Institution, 1885–86, part 2:255–265.

Goode, G. B.

1897. The Smithsonian Institution, 1846–1896. Washington.

Henderson, E. P.

1948. American Meteorites and the National Collection. Annual Report of the Board of Regents of the Smithsonian Institution, pages 257–268.

Henry, J.

1854. Report of the Secretary. Ninth Annual Report of the Board of Regents of the Smithsonian Institution. 463 pages.

Merrill, George P.

1916. Handbook and Descriptive Catalogue of the Meteorite Collections in the United States National Museum. United States National Museum Bulletin, 94.

Tassin, W.

1902. Descriptive Catalogue of the Meteorite Collection in the United States National Museum to January 1, 1902. Report of the United States National Museum for 1900, pages 671–698.

Abbreviations

CHONDRITES:

Enstatite

E

STONY-IRONS:

Pallasite

P

(Type, where known, is indicated by a following digit)

Bronzite

H

Mesosiderite

M

Hypersthene

L

Siderophyre

S

Amphoterite

LL

Lodranite

Lo

Carbonaceous

C

IRONS:

Hexahedrite

Hx

Octahedrite

O

ACHONDRITES:

Aubrite

Ae

Coarsest octahedrite

Ogg

Diogenite

Ah

Coarse octahedrite

Og

Chassignite

Ac

Medium octahedrite

Om

Ureilite

Au

Fine octahedrite

Of

Angrite

Aa

Finest octahedrite

Off

Nakhlite

An

Plessitic octahedrite

Opl

Howardite

Aho

Ataxite

D

Eucrite

Aeu

Anomalous

Anom

List

Weights are given in grams unless otherwise indicated; “s” indicates that only a thin or polished section is present

Name

Locality

Class

Weight

Aarhus

Denmark

H

s

Abancay

Peru

Of

9.8

Abee

Canada

E4

2950

Abernathy

Texas

L6

83

Accalana

Australia

L3

14

Achilles

Kansas

H5

546

Achiras

Argentina

L6

6.8

Adams County

Colorado

H5

569

Adargas

Mexico

Om

24

ad-Dahbubah

Saudi Arabia

H5

40 kg

Adelie Land

Antarctica

L5

69

Adhi Kot

Pakistan

E3

22

Admire

Kansas

P

22 kg

Adrian

Texas

H4

1090

Agen

France

H5

163

Aggie Creek

Alaska

Om

984

Aguada

Argentina

L6

8.0

Ahumada

Mexico

P

834

Ainsworth

Nebraska

Ogg

1635

Akpohon

Canada

Om

64

Akron (1961)

Colorado

L6

70

Alais

France

Cl

0.6

Alamogordo

New Mexico

H5

905

Alamosa

Colorado

L6

1784

Albareto

Italy

L4

1.7

Albin

Wyoming

P

3200

Aleppo

Syria

L6

162

Alessandria

Italy

H5

37

Alexander County

North Carolina

Og

12

al-Ghanim (iron)

Saudi Arabia

O?

500

al-Ghanim (stone)

Saudi Arabia

H6

3755

Alfianello

Italy

L6

680

Algoma

Wisconsin

Om

22

Alikatnima

Australia

D

32

Allegan

Michigan

H5

18 kg

Allende

Mexico

C3

380 kg

Al Rais

Saudi Arabia

C2

132

Alt Bela

Czechoslovakia

Om

10

Altonah

Utah

Of

10 kg

Amates

Mexico

Og

14

Ambapur Nagla

India

H5

45

Amherst No. 1

Nebraska

L6

8017

Amherst No. 2

Nebraska

L6

473

Anderson

Ohio

P

48

Andover

Maine

L6

2791

Andura

India

H6

9.0

Angelica

Wisconsin

Om

331

Angers

France

L6

0.7

Angra dos Reis (stone)

Brazil

Aa

8.5

Ankober

Ethiopia

H4

6964

Anoka

Minnesota

Of

132

Anthony

Kansas

H5

8711

Antofagasta

Chile

P

16 kg

Apoala

Mexico

Om

324

Appley Bridge

Great Britain

LL6

545

Arapahoe

Colorado

L5

422

Arcadia

Nebraska

LL6

1676

Archie

Missouri

H6

3760

Arispe

Mexico

Og

178 kg

Arlington

Minnesota

Om

6140

Arltunga

Australia

D

979

Armel

Colorado

L5

301

ar-Rakhbah

Saudi Arabia

O

395

Arriba No. 1

Colorado

L5

1142

Arroyo Aguiar

Argentina

H5

2.9

Artracoona

Australia

L6

375

Asheville

North Carolina

Om

6.2

Ashfork

Arizona

Og

39

Ashmore

Texas

H5

16

ash-Shalfar

Saudi Arabia

H5

935

Assam

India

L5

7

Assisi

Italy

H5

29

as-Su’aydan

Saudi Arabia

H5

5530

Aswan

Egypt

Om

11

Atarra

India

L4

37

Atemajac

Mexico

L6

8

Athens

Alabama

LL6

206

Atlanta

Louisiana

E5

235

Atoka

Oklahoma

L6

432

Atwood

Colorado

L6

161

Auburn

Alabama

Ogg

235

Augustinovka

USSR

Om

99

Aumale

Algeria

L6

81

Aumières

France

L6

16

Aurora

New Mexico

H4

78

Ausson

France

L5

223

Avanhandava

Brazil

H5

162

Babb’s Mill (Troost’s Iron)

Tennessee

D

133

Bachmut

USSR

L6

9

Bacubirito

Mexico

Off

997

Bahjoi

India

Og

497

Bald Mountain

North Carolina

L4

222

Baldwyn

Mississippi

L6

0.5

Balfour Downs

Australia

Og

911

Bali

Cameroon

C3

154

Ballinger

Texas

Og

459

Ballinoo

Australia

Opl

1415

Bandong

Java

LL6

56

Bansur

India

L6

0.5

Banswal

India

L5

5.7

Baquedano

Chile

Om

864

Barbotan

France

H5

354

Barea

Spain

M

132

Baroti

India

L6

6.6

Barranca Bianca

Chile

Anom

84

Barratta

Australia

L4

4256

Bartlett

Texas

Om

670

Barwell

Great Britain

L5

1463

Barwise

Texas

H5

290

Bath

South Dakota

H4

1086

Bath Furnace

Kentucky

L6

388

Bear Creek

Colorado

Om

275

Beardsley

Kansas

H5

926

Bear Lodge

Wyoming

Om

3265

Beaver Creek

Canada

H4

731

Beddgelert

Great Britain

H5

17

Beenham

New Mexico

L5

4166

Bella Rocca

Mexico

Om

666

Belle Plaine

Kansas

L6

90

Bells

Texas

C2

0.5

Bellsbank

South Africa

Hx

343

Benares

India

LL6

88

Bencubbin

Australia

Anom

7021

Bendego

Brazil

Og

1980

Benld

Illinois

H6

6.3

Bennett County

South Dakota

Hx

8135

Benton

Canada

LL6

225

Bereba

Upper Volta

Aeu

15

Beuste

France

L5

3

Bhola

Bangladesh

L

116

Bholgati

India

Aho

1.6

Bialystok

Poland

Aho

16

Bielokrynitschie

USSR

H4

56

Billings

Missouri

Om

434

Billygoat Donga

Australia

L6

0.6

Binda

Australia

Aho

228

Bingera

Australia

Hx

197

Bir Hadi

Saudi Arabia

H5

525

Bischtübe

USSR

Og

3358

Bishop Canyon

Colorado

Of

226

Bishopville

South Carolina

Ae

630

Bishunpur

India

LL3

42

Bitburg

Germany

Of

168

Bjelaja Zerkov

USSR

H6

10

Bjurbole

Finland

L4

3509

Black Moshannon Park

Pennsylvania

L

29

Black Mountain

North Carolina

Og

18

Blackwell

Oklahoma

L5

2362

Blanket

Texas

L6

1790

Blansko

Czechoslovakia

H6

2.3

Blithfield

Canada

E6

129

Bluff

Texas

L5

8585

Bocas

Mexico

L6

2

Bodaibo

USSR

Of

261

Boelus

Nebraska

LL6

675

Boerne

Texas

H6

537

Bogou

Upper Volta

Og

3107

Boguslavka

USSR

Hx

185

Bolrumilitz

Czechoslovakia

Og

325

Bolivia

Bolivia

Og

20 kg

Bondoc Peninsula

Philippines

M

28 kg

Bonita Springs

Florida

H5

34 kg

Boogaldi

Australia

Of

79

Bori

India

L6

136

Borkut

USSR

L5

8.4

Bowden

South Africa

H5

6.5

Bowesmont

North Dakota

L6

116

Boxhole

Australia

Om

7346

Brady

Texas

L6

60

Brahin

USSR

P

20

Braunau

Czechoslovakia

Hx

241

Breece

New Mexico

Om

541

Breitscheid

Germany

H5

s

Bremervörde

Germany

H3

33

Brenham

Kansas

P

89 kg

Brewster

Kansas

L6

986

Bridgewater

North Carolina

Om

54

Briggsdale

Colorado

Om

60

Briscoe

Texas

L5

260

Bristol

Tennessee

Of

126

Britstown

South Africa

Opl

19

Broken Bow

Nebraska

H4

283

Brownfield (1937)

Texas

H3

1182

Brownfield (1964)

Texas

H5

168

Bruderheim

Canada

L6

5515

Bruno

Canada

Hx

17

Budulan

USSR

M

97

Bununu

Nigeria

Aho

331

Burdett

Kansas

H5

203

Burgavli

USSR

Og

130

Bur-Gheluai

Somalia

H5

3513

Burkett

Texas

Og

1173

Burlington

New York

Om

1325

Burnabbie

Australia

H5

65

Burrika

Australia

L6

0.6

Buschof

USSR

L6

14

Bushman Land

South Africa

Of

2865

Bushneil

Nebraska

H4

50

Bustee

India

Ae

78

Butler

Missouri

Opl

639

Butsura

India

H6

18

Cabezo de Mayo

Spain

L6

207

Cabin Creek

Arkansas

Om

34

Cacaria

Mexico

Om

165

Cachari

Argentina

Aeu

1650

Cadell

Australia

L6

71

Calico Rock

Arkansas

Hx

539

Calliham

Texas

L6

230

Cambria

New York

Of

351

Campbellsville

Kentucky

Om

9521

Campo del Cielo

Argentina

Og

196 kg

Camp Verde

Arizona

Og

541

Canellas

Spain

H5

6.5

Cangas de Onis

Spain

H5

1103

Canon City

Colorado

H5

55

Canton

Georgia

Om

409

Canyon City

California

Om

284

Canyon Diablo

Arizona

Og

1675 kg

Cape Girardeau

Missouri

H6

4

Cape of Good Hope

South Africa

D

209

Caperr

Argentina

Om

36

Cape York

Greenland

Om

8178

Carbo

Mexico

Om

24 kg

Cardanumbi

Australia

L5

0.6

Carlton

Texas

Of

1486

Caroline

Australia

H5

13

Carraweena

Australia

L3

44

Carthage

Tennessee

Om

1399

Cartoonkana

Australia

L6

s

Casas Grandes

Mexico

Om

1317 kg

Casey County

Kentucky

Og

92

Cashion

Oklahoma

H4

71

Casilda

Argentina

H5

203

Casimiro de Abreu

Brazil

Om

212

Castalia

North Carolina

H5

17

Castine

Maine

L6

0.2

Cavour

South Dakota

H6

9285

Cedar (Kansas)

Kansas

H6

191

Cedar (Texas)

Texas

H4

2181

Cedartown

Georgia

Hx

9940

Cee Vee

Texas

H5

130

Central Missouri

Missouri

Ogg

5072

Cereseto

Italy

H5

65

Chainpur

India

LL3

114

Chamberlin

Texas

H5

98

Chandakapur

India

L5

32

Channing

Texas

H5

1530

Chantonnay

France

L6

371

Charcas

Mexico

Om

182

Charlotte

Tennessee

Of

182

Charsonville

France

H6

83

Chassigny

France

Ac

23

Château-Renard

France

L6

727

Chaves

Portugal

Aho

s

Chebankol

USSR

Og

57

Cherokee Springs

South Carolina

LL6

7885

Chesterville

South Carolina

Hx

103

Chico

New Mexico

L

s

Chico Mountains

Texas

Hx

173

Chicora

Pennsylvania

LL6

272

Chihuahua City

Mexico

Anom

363

Chilkoot

Alaska

Om

5524

Chinautla

Guatemala

Of

162

Chinga

USSR

D

1613

Chinguetti

Maurctania

M

409

Chulafinee

Alabama

Om

. 119

Chupaderos

Mexico

Om

2516

Cincinnati

Ohio

Hx

32

Clareton

Wyoming

L6

208

Clark County

Kentucky

Om

2069

Claytonville

Texas

L5

198

Cleveland

Tennessee

Om

819

Clover Springs

Arizona

M

1041

Clovis No. 1

New Mexico

H3

284 kg

Coahuila

Mexico

Hx

147 kg

Cobija

Chile

H6

202

Cockarrow Creek

Australia

L6

3.2

Cockburn

Australia

L6

1850

Cocklebiddy

Australia

H5

119

Cocunda

Australia

L6

s

Colby

Wisconsin

L6

3906

Cold Bay

Alaska

P

287

Cold Bokkeveld

South Africa

C2

37

Coldwater (iron)

Kansas

O

4768

Coldwater (stone)

Kansas

H5

5472

Colfax

North Carolina

Om

312

Collescipoli

Italy

H5

127

Colomera

Spain

Anom

133

Comanche (iron)

Texas

Og

550

Concho

Texas

L6

138

Cookeville

Tennessee

Og

459

Coolac

Australia

Og

2067

Coolamon

Australia

L6

s

Coolidge

Kansas

C4

203

Coomandook

Australia

H6

11

Coonana

Australia

H4

s

Coon Butte

Arizona

L6

199

Coopertown

Tennessee

Og

1149

Coorara

Australia

L6

7.6

Cope

Colorado

H5

4147

Copiapo

Chile

Anom

174

Cortez

Colorado

H6

54

Cosby’s Creek

Tennessee

Og

1375

Costilla Peak

New Mexico

Om

1849

Cotesfield

Nebraska

L6

17

Covert

Kansas

H5

2966

Cowra

Australia

Opl

61

Coya Norte

Chile

Hx

4850

Crab Orchard

Tennessee

M

2047

Cranberry Plains

Virginia

Of

7.9

Cranbourne

Australia

Og

700 kg

Cranganore

India

L6

10

Cratheus

Brazil

Of

42

Credo

Australia

L6

7.4

Crescent

Oklahoma

C2

s

Cronstad

South Africa

H5

12

Cross Roads

North Carolina

H5

6.5

Crumlin

Ireland

L5

35

Cruz del Aire

Mexico

Of

351

Cuernavaca

Mexico

Om

738

Cubertson

Nebraska

H4

12

Çullison

Kansas

H4

2421

Cumberland Falls

Kentucky

Ae

8640

Cumpas

Mexico

Om

2212

Cushing

Oklahoma

H4

519

Cynthiana

Kentucky

L4

643

Dalgaranga

Australia

M

159

Dalgety Downs

Australia

L5

125 kg

Dalhart

Texas

L5

65

Dalton

Georgia

Om

49 kg

Dandapur

India

L6

57

Daniel’s Kuil

South Africa

E6

5

Davis Mountains

Texas

Om

117

Dayton

Ohio

Off

24 kg

Deal

New Jersey

L6

3

Deelfontein

South Africa

Og

105

Deep Springs

North Carolina

D

318

Delegate

Australia

Om

202

Del Rio

Texas

D

237

Densmore

Kansas

L6

42 kg

Denton County

Texas

Om

8

Denver

Colorado

L6

208

Deport

Texas

Og

4455

Descubridora

Mexico

Om

6021

Dexter

Texas

Om

212

Dhurmsala

India

LL6

681

Dimboola

Australia

H5

46

Dimitrovgrad

Yugoslavia

Om

219

Dimmitt

Texas

H4

6285

Dingo Pup Donga

Australia

Au

4.0

Dix

Nebraska

L

8905

Djati-Pengilon

Java

H6

464

Dokachi

Bangladesh

H5

16

Doroninsk

USSR

H6

7.5

Dorrigo

Australia

Opl

39

Douar Mghila

Morocco

LL6

0.5

Doyleville

Colorado

H5

17

Drake Creek

Tennessee

L6

152

Dresden (Canada)

Canada

H6

27

Dresden (Kansas)

Kansas

H5

212

Drum Mountains

Utah

Om

522 kg

Duchesne

Utah

Of

2780

Duel Hill (1854)

North Carolina

Of

138

Dungannon

Virginia

Og

1009

Durala

India

L6

59

Duruma

Kenya

L6

1.5

Dwaleni

Swaziland

H6

115

Dwight

Kansas

L6

174

Dyarrl Island

New Guinea

M

8

Eagle Station

Kentucky

P

345

Edjudina

Australia

H4

0.8

Edmonson

Texas

L6

281

Edmonton (Canada)

Canada

Hx

584

Edmonton (Kentucky)

Kentucky

Of

8277

Efremovka

USSR

C3

269

Ehole

Angola

H5

1528

Eichstadt

Germany

H5

1

Ekeby

Sweden

H4

18

Elba

Colorado

H5

94

Elbogen

Czechoslovakia

Om

94

El Burro

Mexico

Ogg

34 kg

El Capitan

New Mexico

Om

4831

Elenovka

USSR

L5

219

Eli Elwah

Australia

L6

55

Ellemeet

Holland

Ah

s

Ellerslie

Australia

L5

28

Elm Creek

Kansas

H4

1185

El Perdido

Argentina

H5

39

Elsinora

Australia

H5

87

Elyria

Kansas

Om

234

Emery

South Dakota

M

1002

Emmaville

Australia

Aeu

s

Emmitsburg

Maryland

Om

7

Enigma

Georgia

H4

94

Enon

Ohio

Anom

44

Ensisheim

France

LL6

225

Ergheo

Somalia

L5

1082

Erie

Colorado

L

1275

Erxleben

Germany

H6

31

Essebi

Zaire

C2

61

Estacado

Texas

H6

10 kg

Estherville

Iowa

M

10 kg

Esu

Sudan

H

s

Eustis

Florida

H4

480

Eva

Oklahoma

L5

300

Faith

South Dakota

H5

434

Farley

New Mexico

H5

930

Farmington

Kansas

L5

2620

Farmville

North Carolina

H4

5941

Farnum

Nebraska

L5

150

Faucett

Missouri

H5

6209

Fayetteville

Arkansas

H4

161

Felix

Alabama

C3

1286

Fenbark

Australia

H5

4.0

Filomena

Chile

Hx

20 kg

Finmarken

Norway

P

977

Finney

Texas

L5

277

Fisher

Minnesota

L6

6500

Fleming

Colorado

H3

68

Floyd

New Mexico

H4

256

Föllinge

Sweden

Off

14

Forest City

Iowa

H5

36 kg

Forest Vale

Australia

H4

147

Forksville

Virginia

L6

1995

Forrest

Australia

H5

1.7

Forrest Lakes

Australia

LL5

s

Forsyth

Georgia

L6

9.5

Forsyth County

North Carolina

Hx

1121

Fort Pierre

South Dakota

Om

99

Four Corners

New Mexico

Om

7255

Franceville

Colorado

Om

297

Frankfort (iron)

Kentucky

Om

1638

Frankfort (stone)

Alabama

Aho

4.7

Franklin

Kentucky

H5

207

Freda

North Dakota

D

255

Fremont Butte

Colorado

L4

162

Frenchman Bay

Australia

H3

82

Fukutomi

Japan

L5

9.7

Futtehpur

India

L6

19

Gambat

Pakistan

L6

29

Garland

Utah

Ah

102

Garnett

Kansas

H4

286

Garraf

Spain

L6

53

Geidam

Nigeria

H5

5.5

Georgetown

Colorado

H6

687

Ghubara

Saudi Arabia

L5

9

Gibeon

South-West Africa

Of

263 kg

Gifu

Japan

L6

18

Gilgoin

Australia

H5

4285

Girgenti

Italy

L6

8939

Giroux

Canada

P

2381

Gladstone (iron)

Australia

Og

21 kg

Gladstone (stone)

New Mexico

H6

3250

Glasgow

Kentucky

Om

4047

Glorieta Mountain

New Mexico

Om

11 kg

Gnadenfrei

Germany

H5

0.8

Goalpara

India

Au

163

Gobabeb

Southwest Africa

H4

25

Goodland

Kansas

L4

174

Goose Lake

California

Om

1165 kg

Grady (1933)

New Mexico

L

1768

Grady (1937)

New Mexico

H3

772

Grand Rapids

Michigan

Om

3526

Grant

New Mexico

Om

481 kg

Grant County

Kansas

L6

696

Grassland

Texas

L4

114

Great Bear Lake

Canada

H6

40

Greenbrier County

West Virginia

Om

473

Gressk

USSR

Hx

1935

Gretna

Kansas

L5

32 kg

Grosnaja

USSR

C3

4.7

Grossliebenthal

USSR

L6

49

Grüneberg

Poland

H4

16

Gruver

Texas

H4

1256

Guarena

Spain

H6

416

Guffey

Colorado

D

8200

Guibga

Upper Volta

L5

250

Guidder

Cameroon

LL5

0.4

Gun Creek

Arizona

Om

1204

Gundaring

Australia

Og

237

Gunnadorah

Australia

H5

1.2

Gütersloh

Germany

H4

22

Haig

Australia

Om

450

Hainholz

Germany

M

382

Hale Center No. 1

Texas

L5

188

Hale Center No. 2

Texas

H4

324

Hallingeberg

Sweden

L3

144

Hamilton

Australia

L6

201

Hamlet

Indiana

LL4

1543

Hammond

Wisconsin

Om

293

Hammond Downs

Australia

H4

15 kg

Haraiya

India

Aeu

2.2

Hardwick

Minnesota

L4

1091

Harleton

Texas

L6

4400

Harriman

Tennessee

Om

12 kg

Harrison County

Indiana

L6

19

Harrisonville

Missouri

L6

10 kg

Havana

Illinois

Of

12

Haven

Kansas

H6

21

Haverö

Finland

Au

1.8

Haviland

Kansas

H5

84

Hawk Springs

Wyoming

H5

88

Hedeskoga

Sweden

H5

26

Hedjaz

Saudi Arabia

L

107

Helt Township

Indiana

Ogg

135

Henbury

Australia

Om

227 kg

Hendersonville

North Carolina

L5

2695

Hermitage Plains

Australia

L6

130

Hessle

Sweden

H5

1863

Hex River Mountains

South Africa

Hx

582

Hildreth

Nebraska

L5

173

Hill City

Kansas

Of

10 kg

Hoba

South-West Africa

D

4203

Hobbs

New Mexico

H4

224

Hökmark

Sweden

L4

12

Holbrook

Arizona

L6

8454

Holland’s Store

Georgia

Hx

54

Holly

Colorado

H4

37

Holyoke

Colorado

H4

222

Homestead

Iowa

L5

5616

Honolulu

Hawaii

L5

32

Hope

Arkansas

Og

885

Hopper

Virginia

Om

25

Horace

Kansas

H5

464

Horse Creek

Colorado

Hx

140

Hraschina

Yugoslavia

Om

1.0

Huckitta

Australia

P

403

Hugoton

Kansas

H5

258

Huizopa

Mexico

Of

2790

Hungen

Germany

H6

21

Hvittis

Finland

E6

190

Ibbenbüren

Germany

Ah

9

Ibitira

Brazil

Aeu

1.6

Ider

Alabama

Om

90 kg

Idutywa

South Africa

H5

50

Ilimaes (pallasite)

Chile

P

155

Ilinskaya Stanitza

USSR

Om

184

Imilac

Chile

P

19 kg

Imperial

California

H4

4

Indarch

USSR

E4

2840

Indianola

Nebraska

L5

225

Indian Valley

Virginia

Hx

489

Indio Rico

Argentina

H6

4.7

Inman

Kansas

L4

14

Ipiringa

Brazil

H6

10

Iquique

Chile

D

168

Iredell

Texas

Ogg

97

Iron Creek

Canada

Om

122

Itapicuru-Mirim

Brazil

H5

9.7

Ivanpah

California

Om

3115

Ivuna

Tanzania

Cl

122

Jackalsfontein

South Africa

L6

30

Jackson County

Tennessee

Om

46

Jajh deh Kot Lalu

Pakistan

E6

18

Jamestown

North Dakota

Of

329

Jelica

Yugoslavia

LL6

231

Jenkins

Missouri

Og

55 kg

Jenny’s Creek

West Virginia

Og

14

Jerome

Kansas

L4

166

Jhung

Pakistan

L5

22

Joe Wright Mountain

Arkansas

Om

571

Johnson City

Kansas

L6

1955

Johnstown

Colorado

Ah

1028

Jonzac

France

Aeu

0.2

Judesegeri

India

H6

16

Juromenha

Portugal

D

16

Juvinas

France

Aeu

172

Kaalijarv

USSR

Og

4.3

Kaba

Hungary

C3

0.7

Kabo

Nigeria

H5

80

Kainsaz

USSR

C3

26

Kakangari

India

C3?

0.5

Kalaba

Zaire

H4

11

Kaldoonera Hill

Australia

H6

1.4

Kalkaska

Michigan

Om

759

Kamiomi

Japan

H4

5

Kamsagar

India

L6

9.6

Kandahar

Afghanistan

L6

123

Kansas City

Missouri

H5

283

Kapoeta

Sudan

Aho

0.9

Kappakoola

Australia

H6

0.7

Karakol

USSR

LL6

4

Karatu

Tanzania

LL6

57

Karee Kloof

South Africa

Og

27

Karkh

Pakistan

L6

49

Karoonda

Australia

C4

123

Kaufman

Texas

L5

168

Kearney

Nebraska

H5

1008

Keen Mountain

Virginia

Hx

5629

Kelly

Colorado

LL4

3512

Kendall County

Texas

Anom

2044

Kennard

Nebraska

H5

156

Kenton County

Kentucky

Om

2691

Kerilis

France

H5

2.4

Kermichel

France

L6

42

Kernouvé

France

H6

1135

Kesen

Japan

H4

2105

Keyes

Oklahoma

L6

1781

Khairpur

Pakistan

E6

27

Khanpur

India

LL5

30

Kharkov

USSR

L6

26

Khohar

India

L3

92

Khor Temiki

Sudan

Ae

90

Kiel

Germany

L6

6.2

Kielpa

Australia

H5

351

Kiffa

Mauritania

H4

25

Killeter

Ireland

H6

2.5

Kimble County

Texas

H6

4130

Kingfisher

Oklahoma

L5

2260

Kingoonya

Australia

L4

2.4

Kingston

New Mexico

Om

333

Kissij

USSR

H5

22

Kittakittaooloo

Australia

H4

10

Klein-Wenden

Germany

H6

67

Klondike

Canada

D

158

Knowles

Oklahoma

Om

58

Knyahinya

USSR

L5

1575

Kodaikanal

India

Off

283

Kopjes Vlei

South Africa

Hx

64

Koraleigh

Australia

L6

s

Krähenberg

Germany

LL5

4.4

Kramer Creek

Colorado

L4

38

Krasnoi-Ugol

USSR

L6

5.5

Krasnoyarsk

USSR

P

910

Kress

Texas

L6

113

Krymka

USSR

LL3

136

Kuleschovka

USSR

L6

11

Kulnine

Australia

L6

170

Kumerina

Australia

Opl

339

Kunashak

USSR

L6

175

Kuttippuram

India

L6

120

Kyancutta

Australia

Om

754

Kybunga

Australia

L5

94

Kyle

Texas

L6

253

Kyushu

Japan

L6

216

La Bécasse

France

L6

81

Laborel

France

H5

17

La Caille

France

Om

107

Ladder Creek

Kansas

L6

5700

Lafayette

Indiana

An

637

La Grange

Kentucky

Of

2168

L’Aigle

France

L6

448

Lakangaon

India

Aeu

10

Lake Bonney

Australia

L6

s

Lake Brown

Australia

L6

0.2

Lake Grace

Australia

L6

335

Lake Labyrinth

Australia

LL6

1085

Lake Murray

Oklahoma

Ogg

80

Laketon

Texas

L6

124

Lakewood

New Mexico

L6

523

La Lande

New Mexico

L5

158

Lancé

France

C3

185

Lançon

France

H6

73

Landes

West Virginia

O

492

Långhalsen

Sweden

L6

76

Lanton

Missouri

Om

558

La Porte

Indiana

Om

1491

La Primitiva

Chile

Hx

93

Las Vegas

Nevada

Og

2791

Laundry East

Australia

H3

1.0

Laundry Rockhole

Australia

H5

3.1

Laundry West

Australia

L4

2.9

Laurens County

South Carolina

Of

12

Lawrence

Kansas

L6

328

Leedey

Oklahoma

L6

97

Leeds

Canada

Og

20

Lenarto

Czechoslovakia

Om

208

Leon

Kansas

H5

17 kg

Leoville

Kansas

C2

482

Le Pressoir

France

L6

3.6

Les Ormes

France

L5

0.3

Lesves

Belgium

L6

1.5

Lexington County

South Carolina

Og

2617

Lick Creek

North Carolina

Hx

9.7

Lillaverke

Sweden

H5

150

Lime Creek

Alabama

D

2.9

Limerick

Ireland

H5

210

Lincoln County

Colorado

L6

71

Linville

North Carolina

D

15

Linwood

Nebraska

Og

33 kg

Lissa

Czechoslovakia

L6

118

Little Piney

Missouri

L5

78

Little River

Kansas

H6

170

Livingston (Montana)

Montana

Om

294

Livingston (Tennessee)

Tennessee

Om

123

Lixna

USSR

H4

58

Locust Grove

Georgia

Hx

2166

Lodran

Pakistan

Lo

13

Logan

Oklahoma

H5

336

Lombard

Montana

Hx

62

Lonaconing

Maryland

Og

24

Long Island

Kansas

L6

2696

Loomis

Nebraska

L6

229

Loop

Texas

L6

149

Loreto

Mexico

Om

89 kg

Los Reyes

Mexico

Om

377

Lost City

Oklahoma

H5

16 kg

Losttown

Georgia

Om

71

Lowicz

Poland

M

82

Loyola

doubtful

L5

1772

Lua

India

L5

25

Lubbock

Texas

L5

390

Lucky Hill

Jamaica

Om

40

Luis Lopez

New Mexico

Om

174

Lumpkin

Georgia

L6

31

Lundsgård

Sweden

L6

97

Luotolax

Finland

Aho

0.5

Lutschaunig’s Stone

Chile

L6

73

Macau

Brazil

H5

72

Macibini

South Africa

Aeu

15

Madoc

Canada

Om

11

Madrid

Spain

L6

3.5

Mafra

Brazil

L4

9

Magura

Czechoslovakia

Og

672

Mainz

Germany

L5

2

Malakal

Sudan

L5

160

Malotas

Argentina

H5

206

Malvern

South Africa

Aho

19

Manbhoom

India

LL6

15

Mangwendi

Rhodesia

LL6

17

Mantos Blancos

Chile

Of

356

Mapleton

Iowa

Om

3728

Maria Elena (1935)

Chile

Om

11kg

Marion

Iowa

L6

1717

Marjalahti

Finland

P

452

Marshall County

Kentucky

Om

67

Marsland

Nebraska

H5

244

Mart

Texas

Of

454

Matatiele

South Africa

Og

69

Mauerkirchen

Austria

L6

73

Mayday

Kansas

H

5

Mayodan

North Carolina

Hx

13 kg

Maziba

Uganda

L6

390

Mbosi

Tanzania

Om

779

McKinney

Texas

L4

5208

Mejillones

Chile

Hx

12 kg

Melrose

New Mexico

L5

2782

Menow

Germany

H4

110

Merceditas

Chile

Om

724

Mem

Denmark

L6

220

Mertzon

Texas

Om

3319

Merua

India

H5

197

Mesa Verde Park

Colorado

Om

3439

Messina

Italy

L5

3.4

Metsäkyla

Finland

H4

s

Mezö-Madaras

Romania

L3

335

Miami

Texas

H

1160

Mighei

USSR

C2

620

Milena

Yugoslavia

L6

99

Miller (Arkansas)

Arkansas

H5

53

Miller (Kansas)

Kansas

H

41

Mills

New Mexico

H6

367

Milly Milly

Australia

Om

283

Minas Gérais

Brazil

L

10

Mincy

Missouri

M

308

Misshof

USSR

H5

158

Misteca

Mexico

Og

344

Moab

Utah

O

253

Mocs

Romania

L6

3346

Modoc

Kansas

L6

5623

Mokoia

New Zealand

C3

6.4

Molina

Spain

L5

1189

Molong

Australia

P

864

Monahans

Texas

Opl

913

Monroe

North Carolina

H4

252

Monte Milone

Italy

L

0.6

Monze

Zambia

L6

265

Moonbi

Australia

Om

286

Mooranoppin

Australia

Og

149

Moore County

North Carolina

Aeu

460

Mooresfort

Ireland

H5

161

Moorleah

Australia

L6

s

Morito

Mexico

Om

636

Morland

Kansas

H6

517

Mornans

France

H5

32

Morradal

Norway

D

58

Morrill

Nebraska

Om

87

Morristown

Tennessee

M

1757

Morven

New Zealand

H5

112

Mosca

Colorado

L6

6136

Mosquero

New Mexico

H4

1629

Mossgiel

Australia

L4

560

Moti-ka-nagla

India

H6

77

Motpena

Australia

L6

98

Motta di Conti

Italy

H

2.4

Mount Ayliff

South Africa

Og

95

Mount Browne

Australia

H6

486

Mount Dooling

Australia

Ogg

370

Mount Dyrring

Australia

P

672

Mount Edith

Australia

Om

1577

Mount Egerton

Australia

Ae

3731

Mount Joy

Pennsylvania

Ogg

2833

Mount Magnet

Australia

Opl

100

Mount Morris

Wisconsin

E6?

557

Mount Ouray

Colorado

Om

84

Mount Padbury

Australia

M

8147

Mount Sir Charles

Australia

Of

21

Mount Stirling

Australia

Og

383

Mount Vernon

Kentucky

P

134 kg

Muddoor

India

H5

26

Mulga (North)

Australia

H6

278

Mulga (South)

Australia

H4

0.4

Mundrabilla

Australia

Om

217 kg

Mungindi

Australia

Of

573

Muonionalusta

Sweden

Of

419

Murchison

Australia

C2

30 kg

Murfreesboro

Tennessee

Om

125

Murnpeowie

Australia

Anom

191

Muroc Dry Lake

California

L

43

Murphy

North Carolina

Hx

582

Murray

Kentucky

C2

5830

Muzzaffarpur

India

Opl

5

Nagaria

India

Aeu

s

Nagy-Vazsony

Hungary

Og

36

Nakhla

Egypt

An

644

Nakhon Pathom

Thailand

L6

852

Nanjemoy

Maryland

H6

79

Naoki

India

H6

227

Nàrdoo No. 1

Australia

H5

75

Nardoo No. 2

Australia

L6

109

Narellan

Australia

L6

33

Naretha

Australia

L4

2.7

Narraburra

Australia

Om

321

N äs

Sweden

LL6

17

Nashville (Kansas)

Kansas

L6

23 kg

Nashville (North Carolina)

North Carolina

O

2676

Navajo

Arizona

Ogg

517

Nazareth (iron)

Texas

Om

315

Nedagolla

India

Anom

28

Needles

California

Of

10 kg

Neenach

California

L6

2210

Negrillos

Chile

Hx

15 kg

Nejed

Saudi Arabia

Om

2931

Nejo

Ethiopia

L6

183

Nelson County

Kentucky

Ogg

1207

Nenntmannsdorf

Germany

Ogg

15

Neptune Mountains

Antarctica

Og

997

Nerft

USSR

L6

71

Ness County

Kansas

L6

5810

Netschaevo

USSR

Om

267

New Almelo

Kansas

L5

1557

New Baltimore

Pennsylvania

Anom

3216

New Concord

Ohio

L6

8700

New Leipzig

North Dakota

Og

17 kg

Newport

Arkansas

P

222

New Westville

Ohio

Of

3318

Ngawi

Java

LL3

103

N’Goureyma

Mali

Anom

1519

Nikolskoe

USSR

L4

32

N’Kandhla

South Africa

Om

146

Nobleborough

Maine

Aeu

0.1

Nocoleche

Australia

Anom

203

Nogoya

Argentina

C2

4.5

Nora Creina

Australia

L4

8.5

Norcateur ·

Kansas

L6

133

Nordheim

Texas

D

1094

Norfolk

Virginia

Om

110

Norfork

Arkansas

Om

60

Norristown

Georgia

Om

196

North East Reid

Australia

H5

1.9

North Forrest

Australia

H4

3.8

North Haig

Australia

Au

8.2

North Reid

Australia

LL5

4.7

North West Forrest

Australia

E6

11

Norton County

Kansas

Ae

1797

Novo-Urei

USSR

Au

93

Nuevo Laredo

Mexico

Aeu

132

Nulles

Spain

H6

124

Nyirabrany

Hungary

LL5

s

Oak

Australia

L5

0.8

Oakley (iron)

Idaho

Og

111kg

Oakley (stone)

Kansas

H6

1614

Oberlin

Kansas

LL5

195

Obernkirchen

Germany

Of

302

Ochansk

USSR

H4

1668

Odessa

Texas

Og

128 kg

Oesede

Germany

H5

137

Oesel

USSR

L6

28

Ogallala

Nebraska

Og

118

Ogi

Japan

H6

40

Ojuelos Altos

Spain

L

191

Okano

Japan

Hx

20

Okechobee

Florida

L4

968

Okirai

Japan

H5

31

Olivenza

Spain

LL5

938

Ollague

Bolivia

P

296

Olmedilla de Alarcon

Spain

H

314

Orange River (iron)

South Africa

Om

120

Orgueil

France

Cl

183

Orlovka

USSR

H

127

Ornans

France

C3

3.8

Oro Grande

New Mexico

H5

9.1

Oroville

California

Om

401

Orvinio

Italy

L6

59

Oscuro Mountains

New Mexico

Og

102

Osseo

Canada

Og

37 kg

Otis

Kansas

L6

215

Ottawa

Kansas

LL6

12

Oubari

Libya

L4

151

Ovid

Colorado

H

251

Owens Valley

California

Om

157 kg

Ozona

Texas

H

1658

Ozren

Yugoslavia

Og

17

Pacula

Mexico

L6

44

Palo Blanco Creek

New Mexico

Aeu

s

Pan de Azucar

Chile

Og

101

Pantar

Philippines

H5

112

Para de Minas

Brazil

Of

223

Paragould

Arkansas

LL5

31kg

Paranaiba

Brazil

L6

322

Parnallee

India

LL3

520

Pasamonte

New Mexico

Aeu

1585

Patos de Minas

Brazil

Hx

827

Patrimonio

Brazil

L

14

Patwar

Pakistan

M

592

Pavlodar

USSR

P

12

Pavlograd

USSR

L6

97

Pavlovka

USSR

Aho

8

Peace River

Canada

L6

551

Peckelsheim

Germany

Ah

2.2

Peck’s Spring

Texas

L5

629

Peetz

Colorado

L6

810

Pena Bianca Springs

Texas

Ae

457

Penokee

Kansas

H

3552

Perpeti

Pakistan

L6

35

Perryville

Missouri

Opl

14 kg

Persimmon Creek

North Carolina

Opl

3519

Pervomaisky

USSR

L6

446

Pesyanoe

USSR

Ae

67

Petersburg

Tennessee

Aeu

42

Petropavlovka

USSR

H

118

Pevensey

Australia

LL5

14

Phillips County

Colorado

P

368

Piancaldoli

Italy

L3

s

Pickens County

Georgia

H

67

Piedade do Bargre

Brazil

Om

398

Pierceville (iron)

Kansas

Om?

808

Pier ce ville (stone)

Kansas

L

183

Pillistfer

USSR

E6

66

Pima County

Arizona

Hx

150

Pine River

Wisconsin

Om

297

Pinnaroo

Australia

M

1132

Pinon

New Mexico

D

1240

Pipe Creek

Texas

H6

312

Pitts

Georgia

Of

1022

Plains

Texas

H5

363

Plainview (1917)

Texas

H5

24 kg

Plantersville

Texas

H6

1862

Pleasanton

Kansas

H5

204

Plymouth

Indiana

Om

619

Pohlitz

Germany

L5

0.1

Ponca Creek

Nebraska

Ogg

29

Portales No. 3

New Mexico

L

156

Port Orford

Oregon

P

24

Potter

Nebraska

L6

1930

Prairie Dog Creek

Kansas

H3

314

Prambanan

Java

Off

2.3

Pribram

Czechoslovakia

H5

140

Pricetown

Ohio

L6

3.0

Providence

Kentucky

Om

5492

Puente del Zacate

Mexico

Om

2332

Pulaski County

Georgia

Og

112

Pulsora

India

H5

5.8

Pultusk

Poland

H5

3263

Puquios

Chile

Om

90

Puripica

Chile

Hx

15 kg

Putinga

Brazil

L6

962

Putnam County

Georgia

Of

2736

Quartz Mountain

Nevada

Om

57

Queen’s Mercy

South Africa

H6

424

Quenggouk

Burma

H4

35

Quillagua

Chile

Hx

741

Quinn Canyon

Nevada

Om

45

Raco

Argentina

H5

133

Rafriiti

Switzerland

D

22

Rakovka

USSR

L6

23

Ramsdorf

Germany

L6

20

Ranchapur

India

H4

59

Rancho de la Pila

Mexico

Om

54

Rancho de la Presa

Mexico

H

12

Rangala

India

L

26

Ransom

Kansas

H4

295

Ras Tanura

Saudi Arabia

H

5.9

Rawlinna

Australia

H5

2.8

Reager

Kansas

L

37

Red River

Texas

Om

79

Reed City

Michigan

Og

1877

Reid

Australia

H

4.0

Reliegos

Spain

L

26

RenazzO

Italy

C2

26

Rhine Villa

Australia

Og

114

Richardton

North Dakota

H5

5155

Richland

Texas

Hx

1026

Richmond

Virginia

L5

18

Rich Mountain

North Carolina

L6

112

Rifle

Colorado

Og

4367

Rio Loa

Chile

Hx

940

Rio Negro

Brazil

L4

66

Rochester

Indiana

H

53

Rodeo

Mexico

Om

1998

Roebourne

Australia

Om

4018

Rolla (1936)

Kansas

H

414

Rolla (1939)

Kansas

H

10

Rosario

Honduras

Og

190

Rosebud

Texas

H

5

Rose City

Michigan

H5

3587

Rowena

Australia

H6

78

Rowton

Great Britain

Om

32

Roy (1933)

New Mexico

L5

8607

Roy (1934)

New Mexico

L6

4528

Ruff’s Mountain

South Carolina

Om

4762

Rupota

Tanzania

L6

975

Rush County

Indiana

H

4020

Rush Creek

Colorado

L6

3170

Rüssel Gulch

Colorado

Om

72

Sacramento Mountains

New Mexico

Om

6550

St. Caprais-de-Quinsac

France

L

0.4

St. Francois County

Missouri

Og

236

St. Genevieve County

Missouri

Of

1380

St. Germain-du-Pinel

France

H

53

St. Lawrence

Texas

LL6

100

St. Louis

Missouri

H4

2.4

St. Mark’s

South Africa

E5

258

St. Mary’s County

Maryland

LL3

s

St. Mesmin

France

LL6

86

St. Michel

Finland

L6

231

St. Peter

Kansas

L5

549

Saint-Sauveu

France

E4

7.8

St. Severin

France

LL6

2463

Salaices

Mexico

H4

395

Salina

Utah

Om

221

Saline

Kansas

H5

897

Salla

Finland

L

318

Salles

France

H6

50

Salta

Argentina

P

24 kg

Salt Lake City

Utah

H5

2.5

Salt River

Kentucky

Opl

112

Sams Valley

Oregon

Om

19

San Angelo

Texas

Om

3443

San Cristobal

Chile

D

136

Sanderson

Texas

Om

471

Sandia Mountains

New Mexico

Ogg

1672

Sandtown

Arkansas

Om

100

San Emigdio

California

H4

490

San Francisco Mountains

Arizona

Of

1334

San José

Mexico

H5

142

San Juan Capistrano

California

H6

18

Santa Apolonia

Mexico

Om

5689

Santa Catharina

Brazil

D

11 kg

Santa Cruz

Mexico

C2

s

Santa Isabel

Argentina

L6

29

Santa Luzia

Brazil

Ogg

23 kg

Santa Rosa

Colombia

Anom

5751

Santa Rosalia

Mexico

P

63

Santiago Papasquiero

Mexico

Anom

1176

Sao Jose do Rio Preto

Brazil

L5

7.5

Sao Juliao de Moreira

Portugal

Ogg

2150

Saratov

USSR

L4

513

Sardis

Georgia

Og

800 kg

Sarepta

USSR

Og

254

Savannah

Tennessee

Om

27 kg

Schenectady

New York

H5

30

Schönenberg

Germany

L6

8.8

Schwetz

Poland

Om

165

Scott City

Kansas

H5

228

Scottsville

Kentucky

Hx

1042

Scurry

Texas

H5

26

Seagraves

Texas

H4

13 kg

Searsmont

Maine

H5

90

Seeläsgen

Poland

Og

407

Segowlie

India

L6

61

Seguin

Kansas

H

49

Seibert

Colorado

H

131

Seligman

Arizona

Og

147

Selma

Alabama

H4

157

Semarkona

India

LL3

245

Seminole

Texas

H4

457

Sena

Spain

H4

167

Seneca

Kansas

H

265

Seneca Township

Michigan

Of

9372

Seres

Greece

H4

2.0

Serre de Mage

Brazil

Aeu

25

Sevrukovo

USSR

L5

23

Seymour

Missouri

Og

1320

Shalka

India

Ah

88

Shallowater

Texas

Ae

1017

Sharps

Virginia

H3

401

Shaw

Colorado

L6

1596

Shelburne

Canada

L5

735

Shergotty

India

Aeu

270

Shingle Springs

California

D

32

Shrewsbury

Pennsylvania

Om

395

Shytal

Pakistan

L6

27

Siena

Italy

LL5

15

Sierra Gorda

Chile

Hx

17 kg

Sierra Sandon

Chile

Og

72

Signal Mountain

Mexico

Of

41

Sikhote-Alin

USSR

Ogg

4107

Silver Bell

Arizona

Ogg

192

Silver Crown

Wyoming

Og

170

Silverton

Australia

L6

69

Simondium

South Africa

M

9.1

Sindhri

Pakistan

H5

46

Sinnai

Italy

H

17

Sioux County

Nebraska

Aeu

154

Sitathali

India

H5

13

Ski

Norway

L6

1.2

Sleeper Camp

Australia

L6

3.3

Slobodka (1818)

USSR

L4

3.5

Slobodka (1838)

USSR

L

4.0

Smith Center

Kansas

L6

91

Smithland

Kentucky

D

133

Smithonia

Georgia

Hx

590

Smith’s Mountain

North Carolina

Om

57

Smithsonian Iron

Ogg

3400

Smithville

Tennessee

Og

3708

Social Circle

Georgia

Of

22 kg

Soko-Banja

Yugoslavia

LL4

337

Somervell County

Texas

P

80

Soper

Oklahoma

Anom

1122

Soroti

Uganda

Off

154

South Bend

Indiana

P

2.8

South Byron

New York

D

465

South Dahna

Arabia

O

142 kg

South Oman

Arabia

E

13

Spearman

Texas

Om

870

Springwater

Canada

P

2647

Ställdalen

Sweden

H5

192

Stannern

Czechoslovakia

Aeu

497

Staunton

Virginia

Og

6101

Stavropol

USSR

L6

52

Steinbach

Germany

S

427

Stonington

Colorado

H

100

Sublette

Kansas

L

62

Success

Arkansas

L6

3503

Suchy Dul

Czechoslovakia

H5

1.8

Sultanpur

India

L6

71

Supuhee

India

H6

89

Susuman

USSR

Om

74

Sutton

Nebraska

H5

305

Suwahib (Buwah)

Saudi Arabia

H3

5

Sweetwater

Texas

H5

1018

Sylacauga

Alabama

H

1682

Tabor

Czechoslovakia

H5

65

Tadjera

Algeria

L5

69

Taiban

New Mexico

L5

438

Tamarugal

Chile

Om

17 kg

Tambo Quemado

Peru

Om

970

Tané

Japan

L5

586

Tanokami Mountain

Japan

Og

91

Tatahouine

Tunisia

Ah

14

Tathlith

Saudi Arabia

L6

246

Tawallah Valley

Australia

D

1267

Tazewell

Tennessee

Off

1642

Tell

Texas

L6

180

Temple

Texas

L

169

Tenham

Australia

L6

5535

Tennasilm

USSR

L4

4838

Ternera

Chile

D

31

Texline

Texas

H5

646

Thiel Mountains

Antarctica

P

28 kg

Thomson

Georgia

L6

217

Thoreau

New Mexico

Og

294

Thule

Greenland

Om

449

Thunda

Australia

Om

209

Thurlow

Canada

Om

403

Tiberrhamine

Algeria

L6

100

Tieraco Creek

Australia

Om

4038

Tieschitz

Czechoslovakia

H3

31

Tilden

Illinois

L6

903

Timochin

USSR

H5

64

Tirupati

India

H

16

Tjabe

Java

H

39

Tjerebon

Java

L5

s

Tlacotepec

Mexico

D

2400

Tobe

Colorado

H4

5454

Tocopilla

Chile

Hx

1467

Toluca

Mexico

Og

109 kg

Tomatlan

Mexico

H6

168

Tombigbee River

Alabama

Hx

3001

Tomhannock Creek

New York

H5

31

Tonganoxie

Kansas

Om

231

Tonk

India

CI

3

Torrington

Wyoming

H

116

Toubil River

USSR

Om

175

Tourinnes-la-Grosse

Belgium

L6

69

Travis County

Texas

H5

1480

Trenton

Wisconsin

Om

391 kg

Trenzano

Italy

H6

285

Treysa

Germany

Om

195

Trifir

Mali

L

3.0

Troup

Texas

L6

114

Tryon

Nebraska

L

2028

Tucson

Arizona

Anom

911 kg

Tulia

Texas

H5

4917

Turtle River

Minnesota

Om

387

Twin City

Georgia

D

3400

Tysnes Island

Norway

H4

104

Uberaba

Brazil

H5

103

Ucera

Venezuela

H5

205

Udei Station

Nigeria

Om

202

Ularring

Australia

L6

1.2

Ulysses

Kansas

H

334

Umm Ruaba

Sudan

L5

64

Union

Chile

Hx

172

Union County

Georgia

Ogg

84

Ute Creek

New Mexico

H4

177

Utrecht

Holland

L6

40

Utzenstorf

Switzerland

H

105

Uwet

Nigeria

Hx

1105

Uwharrie

North Carolina

Om

1287

Vaca Muerta

Chile

M

1449

Valdinizza

Italy

L6

850

Valkeala

Finland

L6

s

Valley Wells

California

L6

11

Vavilovka

USSR

LL6

3.0

Vengerovo

USSR

H5

34

Vera

Argentina

L4

50

Veramin

Iran

M

52

Verkhne Udinsk

USSR

Om

36

Vernon County

Wisconsin

H

9.3

Victoria West

South Africa

Of

34

View Hill

New Zealand

Om

1883

Vigarano

Italy

C3

2051

Vincent

Australia

L5

s

Vishnupur

India

LL6

24

Vouillé

France

L

161

Wabar

Saudi Arabia

Om

299

Waconda

Kansas

L6

1189

Waingaroraia

New Zealand

Om

600

Waldo

Kansas

L

94

Waldron Ridge

Tennessee

Og

70

Walker County

Alabama

Hx

291

Wallapai

Arizona

Of

303 kg

Walltown

Kentucky

L

3.7

Walters

Oklahoma

L6

25 kg

Warrenton

Missouri

C3

36

Waterville

Washington

Anom

197

Wathena

Kansas

Hx

429

Weatherford

Oklahoma

Anom

1216

Weaver Mountains

Arizona

D

773

Webb

Australia

L6

3.1

Weekeroo

Australia

Og

11 kg

Weldona

Colorado

H

1070

Weiland

Canada

Om

213

Wellington

Texas

H

4224

Wellman

Texas

H5

543

Wessely

Czechoslovakia

H

0.2

Western Arkansas

Arkansas

Of

1672

West Forrest

Australia

H5

2.3

Weston

Connecticut

H4

181

West Reid

Australia

H6

0.8

Weathersfield

Connecticut

L5

290

Whitman

Nebraska

H

21

Wichita County

Texas

Og

2251

Wilbia

Australia

H5

3.8

Wildara

Australia

H5

s

Wiley

Colorado

Opl

189

Willamette

Oregon

Om

2721

Willaroy

Australia

H3

187

Williamstown

Kentucky

Om

1223

Willow Creek

Wyoming

Og

4866

Willowdale

Kansas

H

74

Wilmot

Kansas

H6

133

Wiluna

Australia

H4

284

Wingellina

Australia

H4

s

Winona

Arizona

E6?

224

Witchellina

Australia

H4

156

Wold Cottage

Great Britain

L6

57

Wolf Creek

Australia

Om

350 kg

Wonyulg-unna

Australia

Om

577

Woodbine

Illinois

Of

48 kg

Wood’s Mountain

North Carolina

Of

1786

Woodward County

Oklahoma

H4

44 kg

Woolgorong

Australia

L6

362

Wynella

Australia

H4

431

Yambo No. 1

Zaire

H

4.0

Yambo No. 2

Zaire

L3

3.2

Yandama

Australia

L6

377

Yanhuitlan

Mexico

Of

1200

Yardymly

USSR

Og

81

Yatoor

India

H5

222

Yayjinna

Australia

L6

14

Yenberrie

Australia

Og

3836

Yonozu

Japan

H4

44

York (iron)

Nebraska

Om

30

Youndegin

Australia

Og

5756

Ysleta

Texas

Anom

19

Yurtuk

USSR

Aho

33

Zaborzika

USSR

L

4.1

Zacatecas (1972)

Mexico

Anom

444

Zacatecas (1969)

Mexico

Om

6600

Zavid

Yugoslavia

L6

234

Zebrak

Czechoslovakia

H5

73

Zhovtnevyi

USSR

H

703

Zomba

Malawi

L6

270

Zsadany

Romania

H

13

Zvonkov

USSR

H

40

Chemical Analyses of Two Microprobe Standards

Eugene Jarosewich

ABSTRACT

Chemical analyses are given for two materials for use as microprobe standards: volcanic glass from the Mid-Atlantic Ridge and hornblende from Arenal Volcano, Costa Rica.

Eugene Jarosewich, Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, D. C. 20560.

There has been increasing need for well-analyzed microprobe standards because, as with any instrumental method, a standard compositionally similar to an unknown is the most likely to give reliable results. The key requirements for microprobe standards can be found in the literature in general and some are briefly summarized in an earlier paper (Jarosewich, 1972).

The chemical analyses were performed employing analytical methods described by Hillebrand, et al. (1953) and Peck (1964) except for the determination of sodium and potassium. The latter elements were determined by flame photometry. Data for two new microprobe standards follow.

ARENAL HORNBLENDE USNM 111356.—A green hornblende xenocryst from an andesitic basalt scoria was collected by Dr. W. Melson from the September 1968 eruption of Arenal Volcano, Costa Rica. The sample was crushed and sieved and the 60–100 mesh fraction purified using a heavy liquid (D 3.19–3.21) followed by Franz magnetic separation. The purified sample contains less than 0.5 percent grains with adhering groundmass. An electron microprobe check indicates the sample to be

TABLE 1.—Chemical analyses of two microprobe standards (analyst: E. Jarosewich)

Constituent

Arenal Hornblende (USNM 111356)

Basaltic Glass Juan de Fuca Ridge (USNM 111240/52)

SiO_2

41.46

50.81

Al_2O_3

15.47

14.06

Fe_2O_3

5.60

2.23

FeO

6.43

9.83

MgO

14.24

6.71

CaO

11.55

11.12

Na_2O

1.91

2.62

K_2O

0.21

0.19

H_2O+

1.21

n.d

H_2O-

<0.01

0.02

TiO_2

1.41

1.85

P_2O_5

<0.01

0.17

MnO

0.15

0.22

Total

99.64

99.83

Total Fe

8.91

9.20

n.d. = not determined.

homogeneous within the limits of analytical error.

BASALTIC GLASS USNM 111240/52.—This sample was dredged from the median, flat-floored valley of the southern part of the Juan de Fuca Ridge (44° 40’N, 130°30’W, 2195–2220 m). Approximately 2 percent of the sample is composed of inclusions, primarily plagioclase and olivine. Because the average combined chemical composition of these inclusions is similar to the composition of the glass and because they are present in small amount, the bulk chemistry of the sample is essentially the same as the glass. Electron microprobe analyses shows the glass to be extremely homogeneous in major and minor element content.

Literature Cited

Hillebrand, W. F., G. E. F. Lundell, H. A. Bright, and J. I. Hoffman

1953. Applied Inorganic Analysis. 2nd edition, 1034 pages. New York: John Wiley and Sons.

Jarosewich, E.

1972. Chemical Analyses of Five Minerals for Microprobe Standards. Smithsonian Contributions to the Earth Sciences, 9:83–84.

Peck, L. C.

1964. Systematic Analysis of Silicates. U. S. Geological Survey Bulletin, 1170:66.

Preparation of Multiple Microprobe Samples

Grover C. Moreland and Richard Johnson

ABSTRACT

Several microprobe samples may be prepared simultaneously using a new technique described here. With judicious choice of samples the same technique may be used to prepare microprobe standard discs.

Grover C. Moreland and Richard Johnson, Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, D. C. 20560.

A preparation technique has been developed whereby it is possible to prepare several probe samples simultaneously. The basic mount is a plexiglass disc ¼ inch thick cut from a 1-inch rod. Holes of any convenient size are drilled through the disc and the holes numbered with a scriber. As many as 19 samples can be mounted and prepared simultaneously (Figure 1).

A white 3 × 5 inch card is fastened to a hot plate with masking tape; this card provides a visual contrast against which the sample can be easily seen. A carefully cleaned one inch cover glass is placed on the white card, and the sample disc placed on the cover glass. A weight is added to insure good contact between the disc and the cover glass, and the hot plate temperature adjusted to 40° to 45° C (100°-115° F). Rubber cement is now painted around the edge of the coverglass-plexiglass disc sandwich, and the mount is left on the hot plate for 5 to 10 minutes, or until cured as shown by a brown color.

A mixture of epoxide and expoxide hardener is now prepared (Buehler 20–8130 epoxide and 20–8132 hardener or equivalent). A convenient amount is 4.8 gms of epoxide and 0.8 gm of hardener. This mixture is stirred on the 40° to 45° C hot plate until it reaches a watery consistency.

Each sample is now inserted in its appropriately numbered hole. Then using a dissecting needle, place some of the epoxy mixture on the plexiglass disc and with the needle push some of the mixture over the edge of each hole. The epoxy will run down the wall of the hole, hit the cover glass, and

FIGURE 1.—Schematic of plexiglass disc. (A = Dissecting needle, B = epoxy mixture, C = cross-section of plexiglass disc, D = coverglass, E = mineral grain, F = hole drilled in plexiglass disc.)

rise. This procedure should leave the specimen in contact with the cover glass, with epoxy around and above it, but very little if any beneath it. One can check under a stereomicroscope to see that the sample is resting on the cover glass (i.e., at the bottom of the hole) and that no air bubbles have formed. If these conditions are not met then the samples can be pushed down and air bubbles freed using a small dissecting needle. One then covers the entire upper (numbered) side of the disc with epoxy, thus insuring that the numbers will not be accidentally obliterated during the subsequent steps of preparation and during later use of the disc.

The epoxy mixture should be allowed to dry on the hot plate for about 30 minutes at 50° C (125° F). The card-coverglass-plexiglass disc assembly is then placed in a 50° C oven for about 10 hours. The assembly is then removed from the oven and the card separated from the remainder of the unit.

The samples are exposed by grinding off the cover glass on an 850 rpm lap with a slurry of water and #:600 aluminum oxide. Being careful to keep the lap damp, grind the disc for 2 to 3 minutes or until the samples are exposed. Also grind the numbered side, being careful not to grind off the numbers. The disc should now be washed thoroughly with soap and water and dried.

The samples are now brought to a rough polish by covering a 600 rpm wheel with a double thickness of brown wrapping paper that has been covered with polishing oil and 3 micron diamond compound. (The diamond compound regularly used is VB-3, produced by the Glennel Corp. of West Chester, Pennsylvania.) The disc should be moved counter to the rotation of the wheel; a lapping time of about 5 minutes is usually required. After washing and drying the polish is examined under a reflected light microscope. If necessary repeat the lapping until the only scratches visible are those made by the 3 micron polishing compound. The numbered side of the disc should also be polished to make the numbers visible.

Next, the disc is lapped on a 150 rpm wheel covered with a polishing cloth. The polishing cloth is covered with water to which 0.05 micron alumina is sparingly added until a damp-dry condition is reached. The disc is moved for 30 turns counter to the rotation of the wheel. The disc, same side down, is rotated 180° and given another 30 turns on the wheel. Once again it is washed and dried.

Finally the disc is lapped on a 50 rpm wheel covered with a clean polishing cloth, giving it only 5 turns with light pressure, counter to the rotation of the wheel. This final polishing is to remove any possible contamination due to smearing.

The disc is now washed and dried and examined under a reflected light microscope at about 80 magnification. The 3 micron scratches should no longer be visible and one should see only highly polished, optically flat grains.

One should exercise care in choosing specimens to be mounted in one disc as some very soft material may smear upon polishing and hence cause contamination of the rest of the specimens. Tests were made here on eight samples of varying hardness (metallic zinc, gold, magnesium, aluminum, silver, platinum. Ni-Fe-Co alloy, and lead sulfide (galena)), and mounted and polished on a single disc. A check was made by electron micro-probe to determine any effects of smearing from one sample to another due to the polishing technique. For each sample (sulfur in the case of the galena) the background level above and below the peak was determined. Each sample was then probed for Zn, Au, Mg, Al, Ag, Pt, Fe, Co, Ni, and S. Sulfur was the only element that showed a measurable concentration in some of the other samples on the disc, hence the galena did contaminate the other samples.

Preliminary tests have shown that with judicious choice of samples, microprobe standard discs may be prepared using this technique, thus effecting a considerable saving in time and materials over the one-at-a-time method of polishing microprobe standards.

ACKNOWLEDGMENT.—We wish to thank Charles Obermeyer and William Potts for their assistance in the preparation of this paper.

[1] The original report of Lacroix describing the find site as southwest of Chinguetti was subsequently corrected by Ripert to southeast of Chinguetti (Monod, 1952).