MINERALOGIC NOTES ON PUCHERITE, PYRITE,TRICHALCITE, AND WAVELLITE.
By Earl V. Shannon,Assistant Curator of Geology, United States National Museum.
INTRODUCTION.Minor investigations are constantly being conducted in this lab-oratory for the necessary purpose of accurately ascertaining themineralogic identity of materials. These may be specimens sub-mitted for identification by correspondents, they may be new andunlabeled material to be placed upon exhibition or filed with thereference collections, or they may be specimens already incorporatedin the collections whose labeling is found to require confirmationor correction. These investigations may be conducted by chemical,optical, or crystallograpliic methods or a combination of these asthe case may require. Almost invariably new facts of importance aredeveloped by these studies, and it is desirable that the resultsbe published, firstly in order to permanently record the evidenceupon which the specimen is labeled and secondly because the newdata furnished in regard to the properties or occurrence of rare andunusual minerals are of interest and value to mineralogical sciencein general.It is a practice previously inaugurated in this department to com-bine several of these minor researches, even when they are notdirectly related to each other, into a paper of convenient length forpublication in the Museum Proceedings. In the present contributionthere are assembled short papers on four different subjects : Pyritecrystals of unusual crystallographic development from Arkansas,Pucherite from a new locality in Brazil in measurable crystals agree-ing with those previously recorded on European material and show-ing one new form, Trichalcite from a new locality in Idaho havingoptical properties agreeing with those of the mineral from the originallocality and showing measurable crystals which add new informationregarding the crystallography of this rare arsenate, and Crystallo-graphic and optical properties of wavellite crystals of two specimensfrom Montgomery County, Ark.No. 2455.?Proceedings U. s. National Museum, Vol. 62, Art. 9. 1
2 PEOCEEDINGS OF THE NATIONAL MUSEUM, vol.62.UNUSUAL PYRITE CRYSTALS FROM ARKANSAS.A specimen recently received for examination from Mr. C. A.McClelland of Stillwater, Ark., contains pyrite crystals of such un-usual development as to merit a brief description. The crystals aresmall, averaging less than a millimeter in diameter, and are attachedto the faces of imperfect quartz crystals which line vuggy cavities inwhite quartz. The quartz forms veins up to 2 inches thick in ablack highly graphitic slate. No other minerals are associated withthe pyrite. The crystals all show the simple combination of cubea (100) and octahedron o(lll) both prominently developed. Their
Figs. 1-5.? Pyrite cetstals from Stillwater ,Ark.
claim to distinction lies in their unsymmetrical development. Manyof the crystals are cuboctahedrons of normal proportions. (Fig. 1.)From this habit they vary to long prismatic with the length 10 to 20times the diameter as illustrated in Figure 3, the apparently tetrag-onal prism being formed by the vertical faces of the cube, while theoctahedral planes form a terminal pyramid, often truncated at itssummit by a minute cube face. The faces are practically perfectand free from striations, although some of the long prisms taperslightly, as indicated by the following angular measurements, whichwere made on a crystal of the habit illustrated in Figure 3.
AKT.9. MINERALOGIC NOTES ON PUCHEEITE, ETC. SHANNON.Measurements on elongated pyrite a-ystalfrom Arkansas.
No.
PEOCEEDINGS OF THE NATIONAL MUSEUM. VOL. 62.Pucherite has not heretofore been reported from Brazil and, sincethe crystal measured shows one form new to the mineral, the resultsare presented briefly. Crystallized pucherite has previously beenknown only from Europe, although earthy and pulverulent materialhas been found in Arizona and California.The present specimen is from a weathered pegmatite vein m SaoJose de Bryauba in the Province of Minas Geraes, Brazil. The speci-men consists of a mass of pale yellow earthy bismutite v/hich has afaintly woody structure, as though pseudo-morphous after some columnar mineral.The exterior of the specimen is partly coatedwith the crystalline pucherite, while somepucherite is also disseminated through theinterior of the bismutite mass. The pu-cherite is dull dark brownish red in color andforms crusts of imperfect, intergrown, andsomewhat bruised crystals. Only one crys-tal was measured, and very few of thoseon the specimen are suitable for measure-ment. The crystal measured had the formshown in orthographic and clinographicprojections in Figure 6. The dominantplanes are, as show^l, the base c(OOl) andthe pyramid e(121), with a; (021) andA: (122) as smaller faces. The basal pinacoidc(OOl) gives an excellent signal, whichserves to orient the crystal in polar position.The dome a; (021) also gives very goodsignals, while the pyramid e(121) is wavyand striated parallel with its intersectionwith the base. The pyramid Ic (122) has not previously been recordedfor this species. It occurs as relatively narrow faces giving onlymoderately good signals. The measurements on the crystal aretabulated below: Forms and angles on pucheritefrom Brazil.
Fig. 6.?Orthographic and clino-graphic DRAWING.S OF A PUCHER-ITE CRYSTAL FROM MiNAS GERAES,Brazil.
Letter.
AET.9. MINEEALOGIC NOTES ON PUCHEEITE, ETC. SHANNON.TRICHALCITE FROM SHOSHONE COUNTY, IDAHO.Some years ago the writer had occasion to visit the property ofthe Liberal King claim near the Lookout Mountain mine on the highmountain east of the Forks of Pine Creek in the Pine Creek district,Shoshone County, Idaho. The following account is abstracted fromnotes made at that time:The upper tunnel of this property has developed a vein 6 to 8 feet wide, strikingN. 80? W. and dipping 80? southwest. This vein consists of porous quartz inclosingmuch wall rock. Disseminated in moderate amount through this quartz are sul-phides, mainly pyrite with less chalcopyrite and arsenopyrite and occasionally alittle galena and sphalerite. The porosity of the quartz seems to be an originalcondition and not due to the solution or removal of any primary constituent of thevein. Some coarse-grained galena was seen in a lens of quartz on the hanging wallside of the main vein. Percolating waters have largely decomposed the surfaces ofthe chalcopyrite and pyrite masses, depositing a sooty black secondary sulphide oroxide of copper. More intense oxidation has colored the porous quartz by theformation of brilliant yellow, blue, and green coatings of secondary minerals. Onthe hanging wall of the quartz vein there is a pronounced fissure having a thoroughly
^
Figs. 7-8.-7, Optical and crystallogeaphic structure of twinned crystal op trichalcite. 8,orthograpmc and clinographic drawings of simple tabular ceystal of teichaute.
crushed gouge, which is made up entirely of country rock with no drag quartz. Dis-tributed alon? this fissure are streaks of fine-grained brown sphalerite or finely inter-grown sphalerite and galena up to several inches wide.On the dump of this tunnel there was, at that time, a large pileof the quartzose vein material, which was very highly colored withthe secondary minerals mentioned above. These had the appear-ance of arsenates, and specimens collected at that time gave qualita-tive reactions for arsenic. The bulk of the coatings was exceedinglysmall, however, and, as no facilities for detailed investigation wereavailable, the specimens became lost without their minerals beingdefinitely identified.Recently a typical specimen of this material from the LiberalKing claim has been forwarded to the National Museum by theUnited States Geological Survey as a part of the collection of Mr.
6 PEOCEEDINGS OP THE NATIONAL MUSEUM. vol.62.Edward L. Jones, jr., illustrating his work in this district.^ Theopportunity was thus offered for determining the mineralogical iden-tity of the secondary arsenates wliicli form the brilHant coatings.The ore consists, as has l)een detailed above, of porous white quartzcontaining disseminated sulphides, including pyrite, chalcopyrite, andarsenopyrite, the latter in steei gray orthorhombic crystals. Thereis also some black sphalerite and perhaps a little enargite in the ore.The pyrite is partly coated by the black mineral, probably sootychalcocite, and the quartz is brilliantly colored by thin films of ablue-green mineral with lesser amounts of a yellow-green to yellowmineral and an emerald-green crystalline one.The most abundant of these, the blue-green mineral, has a vitreousto' pearly luster and resembles tyrolite. It gave qualitative chemicalreactions for copper and arsenic. At the request of the writer Mr.A. Rodolfo Martinez very kindly worked out the optical propertiesof this mineral, and by reference to Larsen's tables * it was found toagree with the rare arsenate trichalcite, as shown by the followingcomparison: Comparison of optical properties of trichalcite.Pine Creek, Idaho (Martinez). Turginsk, Urals (Larsen).Color pale bluish-green. Color pale bluish-green.Nonpleochroic. Nonpleochroic.Biaxial. Biaxial.Si<;;n negative (? ). Sign negative (? ).2V large. 2V large.a = . a = 1. 67 ? 0. 01.i3 = 1. 688. /3 = 1. 686 ? 0. 003.7 = . 7 = 1. 698 ? 0. 003.Birefringence medium low. Birefringence 0. 028X normal to plates. X normal to plates.There is no other known mineral containing copper and arsenic acidwhich approaches these properties and, while it is regrettable that themineral is not available in quantity sufficient for analysis, its identitycan be considered as established by these data.Upon examination of the specimen under a binocular microscopeit was found that the mineral was in thin tabular crystals of hexag-onal aspect, and although these were very minute it was found pos-sible to measure two of them on the 2-circle goniometer. The basalpinacoid gave good signals, but the very narrow prismatic planes weremore or less curved and irregular, yielding only approximate measure-ments, accurate perhaps to 1?. These indicated 60? angles for theprismatic zone, the mineral thus simulating hexagonal crystallographic
'Edward L. Jones, jr., A reconnaissance of the Pine Creek district, Idaho. U. S. Geol. Survey Bull.710(0), pp. 1-36, 1919.
< Esper S. Larsen, jr.. Microscopic; detormination of the nonopaque minorals. V. S. Geol. SurveyBull. C79, pp. 1-W and 203, 1921.
ART. 9. MINEKALOGIC NOTES ON PUCHERITE, ETC. SHANNON.symmetry. Examination in polarized light of the measured crystalsshows these to be twins, as shown in Figure 7, made up of biaxialorthorhombic sectors. The sectors, have interlocking boundaries.Each sector has a well-defined cleavage parallel to its free edge, andthe extinction is parallel to this edge. Each sector gives in conver-gent light a perfectly centered biaxial interference figure. The severalapparently prismatic planes of the pseudo-hexagonal tablet thus areevidently pinacoids of the several orthorhombic units which go tomake up the twinned group. This may indicate that the ortho-rhombic form is an inversion product which is pscudomorphous afteran original hexagonal form, but it is more probable that it is merelycharacteristic of trichalcjte to form repeated twins, with the twin-ning plane the unit prism(110), which are pseudo-hexagonal. This is char-acteristic of a greatmany orthorhombic min-erals whose prismaticangle approaches thehexagonal angle, as, forexample, aragonite, with-erite, cerrussite, chalco-cite, etc. Figure 8 isdrawn to show, in ortho-graphic and clinographicprojections, a crystalwhich, while having thesame tabular habit, isuntwinned.Triehalcite has previ-ously been known onlyfrom the original localityin the Urals, the Idahooccurrence thus giving a second locality for this rare arsenate. Theassociated arsenates in the Idaho specimen have not been identified.These include a yellow-green material resembling scorodite and agreen mineral resembling clinoclasite.WAVELLITE CRYSTALS FROM ARKANSAS.A specimen in the Museum collection (Cat. 45211) which shows mi-nute white to brownish-white acicular crystals implanted singly andin groups over surfaces of gray-green variscite was labeled "natroliteon variscite." The specimen was received from Mr. Charles F.Brown and bore this label when received. The unusual associationof a zeolite with a phosphate had not previously been noted, and this60466?23?Proc.N.M.voi.G2 30
Fias. 9-10.?Orthographic and clinographic drawings ofWAVELLITE CRYSTALS FROM ARKANSAS.
PEOCEEDINGS OF THE NATIONAL MUSEUM. VOL. 62.led to a preliminary optical examination which showed that the acicu-lar crystals were not natrolite but were more probably tavistockiteor wavellite. More detailed optical measurements made by Dr. E.S. Larsen indicated that, in all probability, the mineral was wavel-lite. The properties are as follows: Biaxial, positive ( + ), 2Vmedium large, (?60?). Dispersion p>v so small as to be doubtful.Z = c. No principal optical directions perpendicular to the prismfaces. Refractive indices a = 1.525 ? 0.003, ^ = 1.534 ? 0.003,7 = 1.545 ? 0.003. Bu-efringence 0.020 ? 0.003. There are appar-ently three good cleavages normal to the principal optical directions.In order that no question might remain regarding the identity ofthe material, such as could be spared without serious injury to thespecimen was scraped off and examined chemicall}^. Only 0.036gram of pure material was available. This gave a loss on ignitionof 30.09 per cent ( = Il20 + F). The ignited mineral was fused witha large excess of sodium carbonate and the fusion leached with boil-ing water. The residue of insoluble material consisted of 0.0022 gramof FOaOg, possibly largely derived from reagents. It contained nolime. The filtrate gave abundant reactions for alumina and phos-phoric acid.Although the crystals were very minute, averaging perhaps h mm.in length and one-fifth to one-tenth this in diameter, it was foundpossible, after several trials, to secure one which gave satisfactorymeasurements on the 2-circle goniometer. Since, as pointed out byWherry,^ the axial ratios of wavellite are probably variable and arenot accurately known beyond the third decimal place, the anglesmeasured were used to calculate axial values for the best crystalmeasured from the Arkansas specimen. The measurements gave asfollows:
MINERALOGIC NOTES ON PUCHEEITE, ETC -SHANNON.
superior measurements, it is necessary to take the mean value for pofnamely 0.7327. With this value assumed, the forms s(lll) andm(llO) yield for qo the values 0.4161 and 0.4112, respectively. Again,it is necessary to adopt the average of two values, and the axial valuesobtained for the crystal are as follows
:
Po = 0.7327 a = 0.5645^0= .4136 c= .4136The above value for the a axis is practically identical with that ofWherry for the Pennsylvania material (a = 0.5640), while the c axisis somewhat greater than Wherry's (c = 0.4040). The present exam-ination merely adds another observation to the four or five alreadyavailable.In habit the crystals of the Arkansas specimen are not unusual, asshown in Figure 9, the forms being 6(010), m(llO), ^^iClOl), and s(lll),all prominently developed. There is a tendency for the crystals toaggregate in almost parallel position or in sheaves. The prismaticfaces are slightly striated vertically. The angles measured on theonly really satisfactor}^ crystal examined are below compared withthe angles calculated from the above derived values for the axes:
Calculated and measured angles of wavellite.
10 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.62.by crowding, their terminations diverge sufficiently to permit idio-morphic development. Several trials, however, showed that theseare totally unsuited for goniometric measurement, the prismaticplanes being exceedingly wavy, while the broad faces of the dome2? (101) and the narrow faces of the basal pinacoid c (001), whiletransparent, are etched to complete dullness and give only the faintestreflection and no signal whatever. Only qualitative measurementswere obtained, and these indicate the forms present to be &(010),m(llO), 2>(101), and c(OOl). The aspect is chisel-shaped, as shownin the drawing, Figure 10.