Canadian Mineralogist Vol. 18, pp. 519-523(1980)

GEERITE,Gu'.oo$, A NEWCOPPER SULFIDE FROM DEKALBTOWNSH|P, NEW YORK

R.I. GOBLE Deparlment ol Geology, University ol Nebraska-Lincoln, 433 Morrill Hall, Lincoln, Nebraska 68588, U.Sr4..

.GEORGE ROBINSON Route 1, Box 115, Ogdensburg,New York 13669, U.S,A.

Ansrnecr anilite outlined by Goble (1977, in prep.) were performed, an unidentified Geerite is a new minslsl from sulfide from Dekalb Town- (specific ship, St. Lawrence County, New York. It occurs Dekalb Township, locality not as thin black plates and iridescent epitactic (?) known), New York State, was analyzcd on the overgrowths on {110} of . In reflected electron microprobe. A composition of Cur.ssS light. geerite is bluish-white and weakly bireflectant was obtained (energy-dispersive analysis), and with moderate anisotropism in yellow. Geerite has the mineral was tentatively identified as a a welldeveloped cubic subcell, similar to the cell copper-deficient anilite, although - only sphale- of sphalerite, with a 5.410 A; space group F43m. rite-like X-ray patterns could be obtained. Upon The true cell has not been identified. The ideal completion of the leaching experiments on composition for geerite is Cur.ooSwith Z = 4 (cubic " anilite and the identification of subcell); Dc"rc E 5.61 g cm-e. The strongest re- a Cur.eoSstruc- ture, the Dekalb was re-examined. It flections in the geerite powder pattern ldw,r?) mineral (hkl)l are: 3.128 (100)(111). 1.918 (50)(220), was identified as a new mineral, geerite, named 1.637(30)(3 I I ), 1.109(20)( 422\ : the indices refer for Adam Geer (deceased) of Utica, New York, to the cubic subcell. who originally collected the material studied. Both the mineral and name have been approved Keywords: geerite, sphalerite, copper sulfide, by the I.M.A. Commission on New Minerals Dekalb Township, New York. and Mineral Names (May 1978). Sorvrlrerns Puvsrcar AND OPTTcALPRoPERTTES ,On a d6couvert la geerite, nouveau sulfure de cuivre, dans le canton de Dekalb (comt6 St.- Geerite occurs as a thin, iridescent coating Lawrence, New-York, E.U.A.) en minces pla- or as platelets up to approximately 15 pm thick, quettes noires et surcroissances iridescentes (6pi- oriented along {ll0} cleavage planes of sphale- tactiques?) sur {110} de la sphal6rite. En lumidre rite, as shown in Figure l. In some specimens r6fl6chie, la geerite est d'un blanc-bleudtre et 16- geerite is partly or completely replaced by gErement bir6flectante. avec un peu d'anisotropie spionkopite, a new copper sulfide described by jaune. possdde dans le Elle une maille sous-multi- Goble (1980). Other associatedminerals in- ple cubique bien d6vel,opp6e,analogue ir la maille , de la sphal6rite: a 5.410 A, groupe spatial F43m; clude , , azurile, la vraie maille n'a pas 6t6 d6termin6e. La compo- , , , , sition id6ale est Cu1.66S (Z - 4 pour la sous- and . maille); D""r" - 5.61. Les r6flexions les plus Geerite is opaque and appears bluish-white intenses du clich6 de poudre [dnr, (/) (ft&l)l sont: and weakly bireflectant in reflected light. It is 3.128( 100)( l l l ), 1.918 (50) (?20), r.637(30) (3I 1), moderately anisotropic in yellow, with no in- l.109(20)(422), of les indices se rapportent i la ternal reflections. Its polishing hardness is less maille sous-multiple. than that of sphalerite, and it undercuts with (Traduit par la R6daction) respect to that mineral. Small grain size did Mots-crcs. geerite, sphal6rite, sulfure de cuivre. not permit reflectivity and microhardness meas- canton de Dekalb, New-York. urements to be made.

INtnouuctloN X-Rlv er.rp CHEr4tcALDATA

Shortly before the leaching experiments on Samples for X-ray analysis were plucked 519

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Frc. 1. Replacement of sphalerite along {110} cleavage-planes by-geerite' Maximum thickness of geerite platelets is approximately 15 pm' Drawrng af ter photomicrograPh.

subcell has an from polished sections, cleaned in acetone and The very strong pseudocubic equal to that the mounied on glass fibres. The largest sample c parametir approximately -of. patterns ot^-tne-se was 72 x 64 x 16 pcm,resulting in long ex- associatedsphalerite. The X-ray . could easily be posures and low inteisity lines on X-ray films' minerals ari very similar; they powder patterns, where The X-ray powder data given in Table I were confused on the Lasis of and resulting low obtained using a 114.6 mm Gandolfi camera the small size of the sample film'shrinkage correc- with Cu Ka radiation; the intensities were intensity reflections make there is a distinguish- estimated by visual comparison with standard- tions difficult. However, parameter between the scale films.-The pattern was indexed as cubic able difference in the 4 and the 5.398 A of the with a - 5.410 A (precession data), space 5.410 A of geerite reflected most strongly group F43m. with the "ideal" composition associated spialerite, (200) spacing for geerite 6,rr..oS in this cubic cell' the formula Cur'eoS in an increase in the sphalerite on preces- *iA Z - 4 is obtained. Do,r" is 5.61 g cm-'g' relative to the intergrown is also a very notrce' However, the optical data indicate that the sion photographs. There (200) intensity lrelative mineral is only pseudocubic (probably ortho- able weakening of the for geerite compared rhombic). to the ( I 11) intensityl with the associated sphalerite when a direct comparison of precession and Gandolfi films is made. TABLEI. T-RAYSIIiIULATED POIDER DAIA (OAI{DOLFICAiIEM) FORGEERITE Microprobe analyses were obtained using an $D nE ASS0CIATEDSPHALERITT lN C0MPARISoNl,lITH A STAIiDARDSPHALERITE - Applied hesearch Laboratories AMX electron associatql JCPDSStandard sphalerlte N@ber 5-566 ^i"top.ot" equipped with a Tracor Northern OPer- d ril |tk d (l) d (l) NS-S8O energy-dispersive slrctrometer' voltaqe 15 3.128 100 3.121 100 l ll ating conditio.t. w"r": acceierating 2.712 l0 2.706 2.705 l0 200 and beam 1.918 50 r.914 I .91? 51 220 kV,-sample current about 1.5 nA, 1.870* l0 Standards used were: I .683* l0 diameter- about 2 ;r,m. 30 3ll 't.5761.637 30 ZnS, Zn metal for l0 2 222 CuS, Cur.aSfor Cu and S, 6 400 '10 Fe. Apparent concentra- 1.247 1.243 1.240 9 331 Zn arrd Fe metal for 1.209 2 420 corrected for absorption, secondary 1.109 20 l.105 I. t03 9 422 tions were and atomic number effects using a * fluore.scence refl*tion not noted on zero-level precesslon photogfaphs.[9] 9e9r1!9' ptogtam, (Depart- ioi ttri assrciatea sphalerlte, a " 5.398 Ai for JCPDS5-566' seneral ZAF TAPEEMX2 ";S.qiO'lja - 5.406 A. The a parsmters for geerite and the assoclated sphalerlle Sciences, Univer' iere-aeii-rnea fiom precession daia corrected for flln shrlnkage; the frent of Geological Queen's Gandolfj Dwder data rere not corrted for flln shdnkage' but the sp8- oi the analyses are presented in iinsi ot tlre (220) reflectlons rere ln ogre@nt Ylth precesslon dat!' sity). Results

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Table 2. To resolve problems caused by the IAELE2. ELECTRON.IIICROPROBEAMTYSES OF GEERITE undercutting of the softer geerite and uncertain- TraveEe Total Cu:S Zn:S ties about its Zn content owing to its small iluber gC! S %Zn %Fe g ratlo ratio grain-size relative to the microprobe beam, we 71.75 22.93 ndi 94.68 1.58 plotted 68.23 20.52 2.17' 90.92 1.68 0.50 the analyses in Table 2 in Figure 2; 75,05 23.72 ndt 99.77 1.62 analysis total is plotted against analyzed Cu. 63,50 18.35 2.12* 83.97 t.75 0.06 % 68.78 24.04 4.46* 97.28 \.M 0.09 The analyses are plotted with Zn included in 't,44 61.44 21.47 ndr 82.91 the analysis total (circles) and with stoichio- 69.33 ?2,81 nd* 92.14 1.53 (the 70.43 22,71 nd* 93.17 I.56 metric ZnS amount determined from Zn 73.90 23.12 nd* 97.02 I.6t analyses) deleted from the total (crosses). A 70.43 97,76 l.4l 0.04 least-squares fit of those data in which Zn was random 73.36 25.32 nd* 98.68 1.46 rand@ 72.70 24.93 nd* 97.63 1.47 not detected gives a formula Cut.ooS,but with random 76.94 26.04 nd* 102.98 1.49 randm 73.48 24.23 nd* 97.71 t.53 stoichiometric ZnS subtracted from the analyses random 73.9 24,22 5,ll* 102,87 1.53 0.10 the composition is Cur.saS;this may indicate randon 75.28 24.02 5.03* 104.33 1.58 0.10 randon 75.2 25.2 1.0 nd 102.4 t.53 0.02 randm that minor Zn may occasionally substitute for 74.1 25.O 0.9 nd '101.3100.0 t.49 0.02 randm 70.7 25.0 5.6 nd '100.9 1.43 0.ll Cu. Traces of Fe were also detected. randm 71.7 25.1 4.1 nd I.44 0.08 iandm 72.9 a4.a J. I no 100.5 1.50 0.06 To confirm that the specimen used for X-ray randon 72.1 23.5 3.8 nd 99.4 r.55 0.08 randm 70,3 25.5 3.9 nd 99.7 1.39 0.07 analysis was not simply a thin film of copper randm 65.0 25.7 9.2 nd 99.9 1.28 0.17 rand@ 72.7 26.0 3.8 nd 102.5 r.4l 0.07 sulfide coating sphalerite, with the X-ray pat- random 72.1 27.3 2.5 nd l0l .9 1.33 0.04 tern being that of the latter mineral, we floated randm 66.5 21,5 I .8 0.7 90.5 1.56 0.04 the 72 x 64 x 16 sample on silver paint randm nd 33.5 68.5 nd 102,0 - 1.03 W randon nd 33.3 67.8 nd tol. - and analyzed it on the electron microprobe at l 1.03 30 kV accelerating voltage in an attempt to Standards used are CuS and CuBS for Cu and S, Zn retal for Zn, ZnS for Zn* and Fe mtal for Fe. ZAF correcfions applled. Analyses rep- include some of a postulated core of sphalerite resent tilo trayerees acrcss geerlte platelets in sphalerlte p'lus i6 randm geerite and 2 randon sphalerlte polnts; nd designates an in the analyzed total. At the 17 points analyzed, elerent analyzed for but not detected.

-o

9

?' -|ff.,'

o ZnS not detected o ZnS detected,included in totot + ZnS detected, subtrocted from totol

61 62 63 61" 65 66 67 68 69 70 71 72 73 76 o/o Cu

Frc. 2. Microprobe analyses of geerite, with Vo Cu measured plotted as a function of analysis total. For analyses with detectable Zn (O), total Vo ZnS (*) is also plotted. Predicted lines for compositions Cur.r"S, Cu1.sS and Cur.zsS are shown, as is the line fitted to the Zo-free data (f ) bV least-squaresanalysis.

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the average amount of Zn was l,27Vo, cor- calculate the minimum volume percentage of responding to L.9% incorporated stoichiometric copper sulfide present in the sample. The mini- ZnS; the maximum amount of Zn was 4.45Vo, mum and maximum electron penetrations for or 6.6Vo incorporated stoichiometric ZnS. These Zn in geeritewould be l.l5 p,m (Reed 1966) quantities could easily be due to small amounts and 3.75 pm (Castaing 196'0), respectively. of sphalerite intermixed with the geerite plate- Correcting for the 19% stoichiometric ZnS lets, as shown in Figure 1. The theoretical detected in microprobe analyses, these cor- depth-of-generation data compiled in Tables 2 respond to minimum volume percentage of and 3 of Beaman & Isasi (1972) can be used to copper sulfide present in the sample of. l9.l% (1.15 p,m penetration) and 49.3Vo (3.75 y,m. penetration). The data of Shinoda et al. (1968), adjusted for the difference in geerite and copper densities, show that the depth of maximum X- ray production is 0.48 pm at 30 kV, correspond- ing to a minimum volume percentageot ll,5/6 do06.ou. copper sulfide in the sample analyzed. In test (A) sphalerite-anilite mixtures, as little as lO% anilite was readily detectableon Gandolfi X-rpy powder patterns. No such mixture was detected in the sample studied, indicating that the speci- men consists of a single mineral, geerite.

1.6 1.8 2. DrscusstoN rotio With the (1l0)"o""ruouand (006)"*eutncspoc- ings from precessionphotographs and Figure 3, .98 Goble (1977, in prep.), an -1'927r, reprodnced from of Cur.aoSis indicaGd. This uu'J --d110 "ideal" composition ",,.. 0.039 .96 composition was predicted from the data of -?' Goble (1977, in prep.) and correspondsto that dllo.ou,. composition in the system copper-sulfur having .s1 the lowest copper-to-sulfur ratio but still re- 1A) taining cubic close-packing of the sulfur atoms. As describedby Goble (1977, in prep.), pre- .92 cessionphotographs of artificially leached anilite show that with removal of copper, a structure - similar to that of geerite is developed, and the d..^ -l.gg5 .90 Cu:S= JJX=;;-.1 material remains in this structure state meta- 0.039 until the composition approaches that of '1.8 stably 1.0 12 1.1 1.6 2.0 covelline. This is presumably a result of the Cu:S rotio kinetics of the structural changes. Potter (1977) did not detect geerite as a Frc. 3. Correlation of composition with spacing stable phase in the system copper-sulfur. He of planes corresponding to d116 and doos "ou111o" did, howevero report a metastable phase with *veuhe for minerals in the system copper-sulfur. the cdmposition Cur.a!o.rS. As noted above, to one-half The spacing d1r0 coveurnecorresponds synthesized by the leaching of anilite distance measured in the material the sulfur-to-sulfur pseudocubic structure plane of the sulfur atoms in any copper sulfide develops and retains a (i.e., it do€s not itrclude covalently bonded sulfur similar to that of geerite until compositions atoms); d006cweurne corresponds to the average approach CuS. The leached material is distin- spacing between these sulfur planes and may guishable from spionkopite only on single- include covalently bonded sulfur atoms (after crystal patterns; this is probably what was syn- Goble 1977). The d values for geerite are from thesized by Potter (1977), If in fact Potter was Table l; d values for other copper sulfides are looking at materials with a related structure (1974), Potter from the data of Craig & Scott the wrong composition for geerite to (1976) (1980). Open circles but with & Evans and Goble presence of geerite as a stable (Q) indicate theoretical compositions for spion- be stable, the copper-sulfur cannot be kopite and geerite; closed circles ( 3 ) indicate phase in the system measured compositions and d values. precluded.

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Geerite is probably not uncommon, but has ClsrerNc, R. (1960): Electron probe microanalysis. likely gone unnoticed owing to its structural fn Advances in Electronics and Electron phvsics similarity to sphalerite and its intimate asso- 13 (L. & C. Marton, eds.), Academic piess, ciation with that mineral. Geerite probably New York. epitactically upon sphalerite lorms witir CMIc, J.R. & Scorl S.D. (1974): phase (cubic Sulfide {l1o}"pr.r".rt"= {110}s*,rt subcellused), equilibria. /n Sulfide Mineralogy (p.H. and Ribbe, should be looked for as coatings on iri- ed.), Mineral, Soc. Amer, Short Course Norcs descent and altered . I, CSl-l10.

(1977):, PnsssnvettoN oF TypE Metnnrlr Goslr, R.J. The Mineralogy, Composi- tion, and Crystal Structure of Selected Copper Polished sections and a typical hand speci- Sulphides from the Belt-Purcell Supergroup, Southwest Alberta, Canada. men of geerite are preseryed in the collection Ph.D. thesis. Queen's Univ., Kingston, Ontario. of Queen's University, Kingston, Ontario, in the U.S.N.M.N.H. Smithsonian Institution. ( 1980) : Copper sulfides from Alberta: Washington, D.C., and in the New york State yarrowite CueS6 and spionkopite CuseS26.Carr. Museum, Albany, New York. The fragment Mirteral. 18. 5ll-518. used in the X-ray examination is preserved, Porrrn, R.W., U (1977): An mounted on a glass fibre, by one of the authors electrochemical in- (R.J.c.). vestigation of the system copper-sulfur. Econ. Geol. 72, 1524-1542.

AcrNowr,rocEMENTs & Evervs, H.T., Jn. (1976): Definitive X- ray powder data for covellite, anilite, , The authors acknowledge the helpful dis- and chalcocite. /. Res. U.S. Geol, Surv. 4, 205- cussious with Dr. J.D. Scott (Eldorado Nu- 212. clear) concerning the single crystal patterns Rrrp, S.J.B. (1966): Spatial resolution and possible structure of geerite, in electron- and Dr. M.L probe microanalysis. /n Congr, Int. Opt. Rayons Corlett (Queen's University) for her invaluable X Microanal. (4th, Orsay, 1965; R. Castaing, assistance in proving that the material used P. Deschamps & J. Philibert, eds.), Hermann, was indeed a new mineral. Special thanks are Paris. also given to Dr. M. Raymond Buyce (New York State Museum) for making the material SurNooe, G., Munare, K, & Ssrirarzu,R, (1968): available for this studv. Scattering of electrons in metallic targets. /n Quantitative Electron Probe Microanalysis (K, F.J. Heinrich, ed.), Nar. Bur. Stand. Spec. publ. RrrsnrNcrs 298.

BEeMeN, D.R. & Isesr, J.A. (1972): Electron beam microanalysis: fundamentals,-and applications. Received April 1980, revised manuscript accepted Amer. Soc. Test. Mat, STP 506. August 19g0.

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