1305

The Canadian Mineralo gistVol. 34, pp. 1305-1315 (1996)

GALLOBE U DANTITE, PbGasl (AsO4),(SOdl2(OH)eA NEW MINERAL SPECIES FROM TSUMEB, NAMIBIA,

AND ASSOCIATED NEW GALLIUM ANALOGUESOF THE ALUNITE. JAROSITE FAMILY

JOHNL. JAMBOR

Depanment of Earth Sciences, University of Waterlao, Waterloo, Ontario N2L 3GI

DeALTON R. OWENS

CANMET, 555 Booth Street, Ottawa" Ontario KIA 0Gj

JOELD. GRICE

Research Divisiou Canadian Museurn of Nature, P.O, Box 32143, Station D, Ottrwa. Ontarto KP 6P4

MARKN. FEINGLOS

Duke University Medical Center, Box 3Q21, Durham, North Carolinn 27710, U.S.A.

ABSIRA T

Gallobeudantite, ideally PbGar[(AsO),(SOJ]z(OII)e, is the newly defined Ga analogue of beudantite. It occurs as zonedrhornbohedr4 up to 200 pm along an edge, in vugs in a single specimen of massive Cu-bearing sulfides from Tsumeb, Namibia.Gallobeudantite is variably pale yellow, greenish, or cream-colored with a white to pale yellow streak, vitreous luster, evento conchoidal fracture, hardness of 4, and D(calc.) 4.61 glcm3 for Z = 3. The mineral is nonpleochroic, uniaxial negative,c0 1.763(5), € 1.750(5). A single-crystal X-ray refinement of the structure (R = 0.078) showed the mineral to be rhombohedral,space group R3n, a 7 .225(4), c 17,03(2) A, and isostructural with corkite. The strongest lines of the X-ray powder-l{iffractionpattem [d in A(/)(hl

1306 TIIE CANADIAN MINERALOGIST

INTRoDUcrroN

Gallite, CuGaS2, and stihngeite, Ga(OH)3, originallydescribed from occurrences at Tsumeb, Namibia, arethe only previously well-defined minerals containingGa as an essential constituent. The Ga analogue ofjarosite KGa3(SO)2(OH)6 was synthesized byDutrizac (1984), who demonstrated that Ga substitutesfor Fe injarosite-type structures, and that the resultingsolid-solutions are nearly ideal chemically. We reporthere on the natural occurence of extensive Ga substi-tutions in minerals of the jarosite - alunite family asfound in a single specimen from Tsumeb, Namibia.Included in the description is the new species namegallobeudantite, which has been approved by theCommission on New Minerals and Mineral Names"IMA.

Most Ga is commercially produced as a by-productfrom the treatment of bauxite ores, but the Apex minein Utah was unique in that it operated briefly in the late1980s solely for the purpose ofproducing Ga and Ge.These elements at Apex are contained in limonitic oresderived by the oxidation of Cu-Pb-Zn-Ag sulfideveins in dolomite (Bernstein 1986, Hopkins 1985).Jarosite from the Apex deposit was reported to containup to 0.70 wt.Vo Ga (Dutrizac et al. 1986). The newname gallobeudantite alludes to the predominance ofGa in the position occupied by Fe3+ in jarosite-typeminerals. The original specimen is from the privatecollection of one of the authors (M.N.F.), but the singlecrystal used our study of gallobeudantite is in theCanadian Museum of Nature, Ottawa; as well, apolished section of the sulfide-rich matrix of thespecimen, and sections containing the analyzed grainsdescribed here, are in the Systematic Reference Seriesof the National Mineral Collection of Canada" housedat the Geological Survey of Canada, Ottawa. Theoriginal specimen was labeled "fleischerite" and isbelieved to have been collected in about 1960. whenfleischerite was first described: the level of the minefrom which the specimen was extracted is not known.Tsumeb is a world-famous mineral locality partlybecause of the unusual geochemistry of its primaryores, and partly because supergene alteration has led tothe development of an extensive suite of secondaryminerals, many of which are of display quality.Beudartite, and now gallobeudantite, are among theminerals in the secondary suite.

GAI-L0BEITDANTnE

Gallobeudantite occurs in vugs in a single, blackishspecimen of massive copper ore, approximately3 x 5 x 1.5 cm. The vugs are megascopicallyinconspicuous, and the crystals within the vugs arenot noticeable unless examined with a binocularmicroscope. A polished section of one end of thesoecimen showed that the host material consists

42.5 A.4 42.3 32.7 32.6 32.1 62.4 61.9 63.82.0 2.0 2.t 0.7 1.7 2.3 0.5 0.4 0.4

13.3 13.5 13.2 1.4 1.1 t-7 2.0 1,7 1.60.4 0.5 0.5 32.1 31.2 31.0 0.4 0.4 0.37.5 7.6 1.9 0.4 0.6 0.1 6.4 63 6.1t.8 1.9 1.1 0.0 0.0 0.0 1.6 1.6 1.4

32.6 32.4 32.8 33.t 329 32.9 n.4 AA &3.100.1 100.3 100.5 t01.0 100.7 100.7 100.7 993 99.9htuata, 33 tutu ftftula 4 dorc fomta 2A atotu

10.57 10.55 10.49 Cul.m l .@ 0.98 Cu6.89 6.94

0.49 0.49 0.5011.06 11.04 10.99 Ca 0.91

s 12.00 12.00 l l.6E

Cu, wt%ZlFeGaGe

ssm

LU

Zn

FeGa

Ce

Fe 0.053-76 3.83 3.72 Zn 0.020.09 0.ll qll Ge-oJ!3.85 3.94 3.83 0.99

r.63 r.66 l.n S 2.01!.3! gio 0J62.0t 2.06 2.08

7.150.041.19

0.600210.030.140.98

zn 9M. S,040.87 0.87 6.9s 6.980.06 0.060.05 0.07 Ce 0.62 0.OoJE 0]02 Fe 0.25 0211.00 1.02 Go 0.04 0.04

As oJl oJl2.00 2.00 1.06 1.02

s 16.07 15.97 16.ll

Analys d 20 kV, 20 nA, 2$mnd @unt ntg TtMr Northm PRZ @r4lion

prcgm. Stsdeids: chal€prrib (Cu"Fe,Sl synthetic Fetu2 (A3), Ce neel (Ge)'

synthdio TmJcqorz (Ca), $halerite (Zn).

mainly of aligned inclusions of renierite, up toI x 3 mm, in a granular matrix consisting largely ofa mineral that gives a germanite-like X-ray powderpatlern, but with a composition much too Cu-rich to begermanite (Table 1); the latter is under further study.The renierite (Table l) contains irregular inclusions ofgaUite (Table 1) up to 75 pm across, and one end ofthesection is texturally complex and contains inclusionsof Sb-free gallian (0.3 .trt.Vo Ga) tennantite. A thinrim of chalcocite emphasizes the granular texture ofthe germanite-like phase, and all minerals are cut byirregular, hairline veinlets of chalcocite.

Disseminated on the surface of the specimen arelocal, minute patches of hematite and goethite, sparsecrystals of stolzite, and dots of spongy mercuriansilver. One end of the specimen has a thin, discon-tinuous veinlet, about 1 mm long, of otjisumeite,PbGe4Oe.

Pltysical and optical properties

Gallobeudantite occurs in the vugs as zones withincrystals that show an extensive range of mutual solid-solution involving As, P, and S. The crystals aresparsely disseminated rhombohedra up to 200 pmalong an edge. Some of the rhombohedra show a minormodification by {001}. Single, compositionally zonedcrystals do occur, but most are multiple grains, toosparse to be described as aggegates. Most crystals are

evenness may be an indication of the {001 } cleavagethat is present in other members of the beudantitegroup. Density could not be measured because ofthe small grain-size; for Z = 3, Dcac is 4.87 g/cm3for the idealized formula and AsOo:SO4 = li|.Gallobeudantite is nonfluorescent, and in immersionoil is nonpleochroic, uniaxial negative, ro 1.763(5),e 1.750(5) at 589 nm.

Composition

Electron-microprobe compositions for gallo-beudantite were obtained with an JEOL 733 instrumenroperated at 15 kV and with a beam current of 20 nA,using l0-second counting times, the Tracor NorthernPROZA correction program, and the followingstandards: apatite @) from Durango, Mexico, Ge metal(Ge), and synthetic GaAs (Ga), ZnFe"Oo (Zn,Fe),PbSO4 Gb,S), A12O3 (Al), InAs (As), and CaTiSiO5(Ca). As most of the analyzed zones were found to beslightly unstable under the electron beam, analyzedareas were restricted as much as possible to those withdimensions large enough to permit movement of thespecimen during data acquisition. Gallobeudantite wasamong the least stable phases, and the POo analoguewas the most stable.

Figures I to 7, inclusive, illustrate typical zonedgrains containing gallobeudantite, for which electron-microprobe compositions are given in Table 2. Theaverage composition derived from six analyses in

Flo. l. Back-scattered-electron @SE) image of zoned graincontaining areas of gallobeudantite (analyses 4.2, 4.4, and,4.7 in Table 2). Znne 4.3 is a PO, aaalogue Qable 3). Anarow outermost zone, not visible in the photograph,consists of the Ga analogue of arsenocrandallite. Bar scalerepresents 10 pm.

r3w

Flc. 2. BSE image of poorly polished grain consisting ofGa analogue of segnitite (arca 2.2, Table 2) and gallianhidalgoite (2.1, Table 3). Bar scale represents 50 pm.

FIc. 3. BSE image of zoned grain consisring of gallo-beudantite (7.1, Table 2), gallian beudartite (7.0, Table 3),and gallian hidalgoile (7 .2, Table 3). Outerrnost zone (7.3)is the Ca analogue of gallobeudantite. Bar scale represents20um.

GALLOBEUDANTITE" A NEW MINERAL SPECIES. TST]MEB. NAMIBIA

1308 TI{E CANADIAN MINERALOGIST

Fro. 4. BSE image of zoned grain consisting of gallo-beudantite (5.4, Table 2; 5.0 and 5.2 are similar). Darkouter zone (5.7) is gallian hidalgoite. Bar scale represents20 pm.

Table 2 is Pb1.sa(GaszeFeffizAb.ozzoo.rd6.6[(AsOJr.r+(SOro.sol>2.00(Olt)s.sa, which is the Ga analogue ofbeudantite, idealized as PbFel+[(AsOr,(SOr]2(OH)6.As is evid9nt from Table 2, Gu Fe, and Al showconsiderable mutual substitution in the mineral.whereas that involving Zn and Ge is minor. The XOa

FIG. 6. BSE image of zoned grain in which dark core (X)consists of POo analogue of gallobeudantite (PS3-AI inTable 4), and light grcy zote (X 2) is gallobeudantite.Bar scale represents 50 Pm.

position is characterized by a predominance of (AsO),substantial substitution of (SO) for (AsO), andnegligible @O). The predominance of (AsO/ in zone6.1 Cfable 2) is sufficiently large that the compositioncorresponds to the Ga analogue of segnitite, the latterideally PbFel+H(AsO/2(OFI)6. The compositions of

Rc. 5. BSE image of zoned grain consisting of core of gallianbeudantite (2.0, Jable 3) rimmed by POa analogue ofgallobeudantite,(2.2,Table 4), which is.in tur4 rimmedby grillobeudantite Q.1\ Tahle 2); area 2.3 is Al-tich(up to l0 wt.Vo y'.J,2O) gallobeudantite. Bar scalerepresents 20 Pm.

Frc. 7. BSE image showing POa analogue of gallobeudantite(PS3-D, Table 4) and a whiter zone of gallobeudantite.Bar scale represents l0 pm.

GALLOBEUDANTITE, A NEW MINERAL SPECIES, TST]MEB, NAMIBIA

TASLB 2. ELECTROTI.MICROPROBE COMPOSITIONS OF GALLOBETJDANITIE TABLE 4. ELECIRON.MICROPROBE COMPOSMONS OF Pb-CnPHOSP}IATE

PbO, wt.%CaO7aO@2GarOrFerO.dro.A&o,s03Prot

[H,o]*

1309

Fis. l Fis.2 Fi&3 Fis.4 Fis.542 4.4 4.7 2.2t 1.1 5.4 z.la 6.1 63

Pbo.rvtrlo 32.1 30.8 32.2 29.7 30.4 30.1 30.4 29.6 30.8cao 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0ZnO 22 0.6 2.0 0.0 0.6 0.6 0J 0.0 3.4Ga.o, 192 18.4 20.0 19.5 18.5 19.8 19.8 17.6 31.6FerO, Z9 122 3.1 4.7 13.3 10.6 10.1 4.0 1.3Alros 8.9 2.3 8.1 5.5 1.5 3.0 3.0 7.6 0.9Aqo, 16.0 18.6 16.6 25.0 l8.l 18.7 m2 X.9 92so: 10.5 9.7 to.1 J.0 9.0 9.0 82 5.7 t3,7PrO, 02 0.0 0.5 02 0.0 0.0 0.0 0.0 0.9CaO, 0.6 0.0 0.0 2.6 0.0 0.0 0.0 29 0.0Fr.ol"* 8.3 _6J

'7.8 _61 JJ J,L 32 J.9 7.e

100.9 99.3 101.6 98.1 98.5 9.t 9,7 98,3 99,7

Fig. 1 Fig.5 Fig.6 Fig.74.3 2.2 PS3-A1 PS 3-6 PS3-D

31.7 33.1 32.5 32,3 33.20.0 0.0 0.0 0.0 0.00.0 0.0 0.0 0.0 0.00.0 0.0 0.0 0.0 0.0

24.5 263 26.9 26.3 27.4t0.7 9.2 7.6 6.4 7.Ot.7 2.6 3.0 3.2 2.61.1 0.0 0.0 0.0 0.85.5 6.0 6.5 6.5 5.5

!4.S 15.8 t5.2 t4.2 t5.489.2 93.0 9r.7 88.9 9r.9

Pb 1.04 1.03 1.02 1.04 1.07 1.04Ga l.9l 1.96 2.A 2.03 2,10 2.0OFe 0.98 0.80 0.67 0.O 0.63 0.73Al 924 0.36 9A2 0.45 0.37 932

3.13 3 . t2 3 .11 3 .10 3 . i0 3 .10P 1.44 1.55 t.s2 1.44 1.5s l.sls 0.50 0.51 0.s7 0.58 0.49 0.54A s 9 . 0 Z j - - 0 , 0 5 O . 0 2

2.Ot 2.06 2.09 2.02 2.09 2.07oH 5.95 5.74 5.64 5.89 6.20 5.74

Avg.

32.5:

26.288.182.620.386.@

14.9690.98

. / s98.34

fmlla&tlaW

Pb 1.00 1.03 1.00 t.ll l.m 1.00 l.l7 0.98 0.98

7iCa

AI

AssP

(on 6.41 5.55 6.t2 5.57 5.86 t.90 s,69 5,12

.Cooposnio c(mpods 10 Ga ealog@ of segnttite

various zones in the gallobeudantite-bearing grains(Tables 2,3, 4), and the implications for nomenclature,are discussed in later sections.

TABLE 3. ELECTRON.MCROPROBE COMPOSMONS OFGALLIAN HIDALGOITE AND BEIIDANTITE

Hidalgoite Beudmtite

Fig. 3 Fig.2 Fig. 4 Fig.3 Fig. 5

fomubfor I4O

X-ray data

Debye-Scherrer X-ray patterns obtained with114.6-mm cameras and CoKcr radiation indicate thatthe compositional variations in the zoned crystals donot have an extreme effect on the cell dimensions.Although the X-ray powder pat0erns of aggegates ofthe zoned crystals are not sharp relative ta, e.g., thepowder pattern of quartz, neither are they unusuallybroad or diffirse, and there are no signs of the multiplelines that would appear if solid solution radicallyshifted the cell dimensions. None qf the diffractionpattems was observed to have an 11 A diffraction line,the presence of whicl would indicate n 66ufling ofthe c axis to -34 A" as occurs in some membersof the beudantite group and in the alunite - jarositefamily, with plumbojarosite perhaps the best knownexample.

The crystal structure of gallobeudantite wasdetermined from a fragment extracted from the areamarked 4.7 in Figure 1. The material extricated fromarea 4.7. which also included a small amount ofpowder, gave a Gandolfi patlern that is spotty butotherwise matches well the pattern of a bulk sample aslisted in Table 5. Gallobeudantite is rhombohedral,space group R3m. T\e crystal-structure determinationgave o7.zis1l), c r7.03(i) A.,vllo(t) A3. An energy-dispersion analysis of this single-crystal fragmentconfirmed the absence of P.

0.19 0.06 0.17 - 4.07 0.06 0.04 - 029t.43 tA7 1.48 l.J9 1.49 lJ6 1.53 t.39 2"40025 t.t4 0.32 0.45 126 0.98 0.q7 0.31 0.12121 033 1.10 0.74 022 0.44 0.43 l.t0 0.13o . o 4 - 0 . 0 1 0 ' U j i - O 2 0 i3.12 3.00 3.12 2.n 3.04 3.M 2.97 3.M 2,94

0.9.6 l2t 1.00 1.66 1.19 l:0 128 1.55 0J70.91 0.91 0.93 0.48 0.85 0.83 0.75 0.53 t.D0 . A A j i 9 , A - - - - 0 2 11.89 2,12 1.93 2.16 2.U 2.03 2.03 2.08 2.N

PbO,wt.%CaOZaOGqotFero,AlrosAsrqSo,PrO,GeO,

Pb 1.05

ZrL 0.07Ga 1.13Fe 0.31Al 1.53Ge 0.02

3.06

As 1.15s 0.79P 0.02

t.96(orD* 6.17

2.t 5.7 7.032.9 32.7 31.60.0 0.0 0.00.0 0.5 0.0

12.6 18.3 t2.65.9 2.6 t9.7

11.3 10.8 1.5t7.5 17.5 24.611.0 9.7 6.50.0 0.5 0.90.0 0.0 0.0

91.2 92.6 93.4

1.02 t.02 1.06

7.233.50.00.9

15.2J . O

11 .118.99.00.20.3

E2.7

2.029.60.00.2

lt.222.20.2

20.28.00.20.6

92.4

0.99

0.020.892.W0.030.043.05

1.320.750.022.095.65

0.041.35 1.010.22 1.851.46 0.n.--: :3.07 3.08

1.05 1.340.84 0.61_q44 0.r01.93 2.056.24 5.84

0.940.51l . ) )

' :3.00

1.060.95-2.015.95

1310 T1IE CANADIAN MINERALOGIST

TABLE 5. REPRESENTATIVE X.RAY POWDER DATA FOR TABLE 6. GALLOBETIDANTITE: STRUCTL'RE-DETERMINATION DATA

*114.6-m Debye-Scherrer cmerE CoI( X-mdiation. Lines withm rterisk rere used for the unit-cell refinement indexed with a7.184" c 17.077 4..

Crystal structure

The fragment of gallobeudantite used for thecollection of X-ray-diffraction intensity data isdesignated as CMNMI 81518. Single-crystalprecession photographs gave the space-group choicesR32 (155), R3m (1.60), and R3m (166) on the basis ofsystematic absences of reflections. Intensity data werecollected on a flrlly automated Nicolet R3n four-circlediffiactometer. A set of. 22 reflectrons was used toorient the crystal and to refine the cell dimensions.Three asymmetric sets of intensity data were collectedup to 20 = 55o using a 0:20 scan-mode and variablescan speeds of 3 to 29olminute. Data pertinent to thecolection of the intensity data are given in Table 6. Forthe absorption correction, four intense diffraction-maxima in the range 13 to 50' 20 were chosen forry diffraction-vector scans after the method of Northet al. (L968). Structure determination and structurerefinement were done using the SHELXTL (Sheldrick1990) package of computer programs. The crystal'sirregular shape, precluding a good absorption-correction, became the limiting factor in the structurerefinement. This problem in the data reduction isevident from a merging R of l3.l%o for the threeasymmetric units of reflection data.

Idealfomula: N Pbca3[(AsOJ,(SOJ]r(OH)6Spregroup: R3n(160)Crystal size: 0.12 x 0.12 x 0.06nm

Radiation:Opelatingmnditions:p: 28m'lMia. aanmissioa 0.143Mu. tnnsmission: 0.803

vx = Dr(lr, I - | r"lfnw r/tz, r= F'?(r' )l-r

Normalized structure-factor statistics, lP - tl =0.793, indicate an acentric space-group. The E-mapcoordinates were assigued to appropriate scatleringcurves, Pb, Ga, As, S and six O atoms in R3z. Thisstructure model refined to R = 8.0Vo. The equivalentmodel in R3 refined to R = 10.0Vo, and n R3m, toR = 9.LVo. In the final least-squares refinement, thesites of all cations were refined with anisotropicdisplacement-factors. The addition of an isofropicextinction-correction did not improve the refinement.In the final AF-synthesis, residual electron densitiesremained, but none of these could be satisfactorilyassigned to H atoms. The final positional anddisplacement parameters for the gallobbudantitestructure are given in Table 7, and selected bond-lengths and angles, in Table 8. Observed andcalculated structure-factors have been submitted to theDepository of Unpublished Data, CISTI, NationalResearch Council of Canada, Ottawa, Canada KlA0s2.

Gallobeudantite is isostructural with corkite,PbFer[(SO/,(Por]2(oH)6, (Giuseppetti & Tadini1987), with Ga replacing Fe and As replacing P withinthe crystal structure. The Pb site refines off the origin,

TABLE 7. GALLOBEUDANTITE: ATOMIC CoORDINATESAND ISOTROPIC DISPLACEMENT FAcToRs (A x l0)

ATOM x

I6

90l )

405

100253030l 0I

40l 553030

I5l 01l0l )

5

d*

s.855.003.593.523.0382.9202.8512.513

2.2992.2712231

1.948t.7971.7591.7151.6931.6781.6461.519t.497r.4a9

1.4001.38413201.285

5.855.033.593.523.03829232.8462.5142.3302.3002.2712.2312.060r9491.7961.7601.7171.6931.678t.6471 .5191.4971.4091.4081.lmo

hkt

l 0 lo121 1 01041132028006*024*21lE205107*t 163214303t220,208*131z'17*I 1g*

1.0.10226'

0.2.10Nt ) I

232039N

Mo/gmphite monocbmmator50 kV/40 mA

a=7.us(4) Ac= t?.03Q) A't/=770(1)

|:Z = 4Totalrcfl.1290f miqre496

i(in| 13.t%Fo> 6c(F1416

Final i = 7.8%FimlwR=6,7%

y z U e q

PbGaAsSol02o3o4oH1or12

0.020(4) -0.014(0 0 4u(53)0.ee78(D 0.4989(4) 0.4991(3) 154(9)0 0 0.6825(3) 84(10)0 0 0.3011(8) 206Q3)0 0 0.579(1) 2000 0 0.394(l) 2000.7s2(3) 0.876(l) 0.7Dq, 159(35)0.216Q) 0.784Q) 0.%18(e) 288(44)0.45sQ) 0.e0e(3) 0.803(t) 260(42)0.873(1) 0.746Q) 0.8660) 3q27)

TABLE 8. GALLOBEUDANTITE: SELECIED BONDLENGTT{S (A) AND BOND ANGLESE)

131 I

as was found for the centric structure of beudantite(Szymardski 1988). This shift within the polyhedronis a result of the stereochemically inactive lone-pairelectrons associated with Pb. an effect that has beennoted in the structure of several minerals (Gice et al.1991). As in corkite and beudantite" the Pb-Opolyhedron is an icosahedron with the six Pb{ bondlengths being longer than the six Pb-OH bond lengths:gallobeudanlte Z.SZ Lversus 2.78 A, corkite Z9Z Aversus 2.73 A (Giuseppetti &^ Tadini 1987), andbeudantite 2.87 L versus 2.80 A (Szymafski 1988).The Ga site-occupancy refines to an atomic scatteringpower of 24.8 elecffons* which compares well with themicroprobe results of 25.1 elecffons for the combinedelements G4 Al, Fe,7n, and Ge in the analysis of area4.7 in Figure 1 (Table 2). The Ga polyhedron is aslightly distorted octahedron Clable 8). The Ga poly-hedra form (001) sheets of corner-sharing polyhedra(Frg. 8).The two tetrahedra sites [AsOal and [SOa] arealigned along t0011 (Fig. 9). The sites are well ordered,with site-occupancy refinements of 31.9Q) electons(As site) and 16.5(7) electrons (S site). Therefinementsare both within 2o of the ideal scattering power of Asand S, respectively. Similarly, ordering of the sites isdemonstrated by^the average bondJengths, 1.70 A forAs-O and 1.55 A for S-O, which are in keeping withother arsenates and sulfates. It is the ordering of thesetwo tetrahedron sites that lowers the symmetry fromRSmto R3m.

GALLOBETJDANTITE" A NEW MINERAL SPECIES, TSIJMEB, NAMIBIA

Pb-o3Pb-o3Pb-o3Pb-o4Pb-04Pb-o4(Pb-o)

Pb-O ICOSAHEDRON2.6(3) Pb-OH12.97(s) Pb-oHl2.69(4) Pb-OHl2.58(4) Pb-Orr22.96(4) Pb-OH22.99(3) Pb-OH2Q.825> (PbOH)

2.nQ)2.uQ)2.66Q)2.73(2)2.71(2)2.e0(3)p.777t

178.1(7)86.1(7)x295.7(6) x2/2.5(7) x285.7(6'1x286.1(6)177.9(6) x293.0(6) x 287.e(5)

112.2(6)x3106.6(6) x 3(109.4)

106.7(l)x3112.2@x3(r0e.4)

ca-O OCTAHEDRONGa-O3 1.99807) O3-o4Ga-O4 1.956(16) O3-oH1Ga-OHl 1.9n(Dx2 O3-OH2GB-OIi2 1.982Q)x2 O4-OH1

o4-o112(Ga-o)

13t2

NoNTENCLATURE

Beudantite has the ideal formula PbFe[(AsOJ,(50112(0II)6, and the stucture is rhombohedral, spacegroup R3n (Szymarlski 1988, Giuseppetti & Tadini1989). Although ordering of As and S lowers thesymmetry of gallobeudantite to R3rn, the effects oforder can be more pronounced, and may lead to adquUing of the c axis or to changes in symmetry (e.g.,Cowgill et al. 1963, Radoslovich 1982, Jambor &Dutrizac 1983). To accommodate changes in symmetryand the compositional variations, various subdivisionsof the alunite - jarosite family (which includesbeudantite and corkite) have been proposed (e.9., Scott1987, Nov6k et al. 1994). The system ofnomenclatureapplicable to this family is currently under review(Jambor et al. 1995). Although the IMA-approvednomenclature is not consistetrt in all cases (Jamboret al. L996), in this paper we rigidly follow Scott's(1987) MA-approved system for compositionboundaries, despite its limitations (Bhch et al. 1992,hing et al. 1995). Thus, tle simple Pb-dominant

THE CANADIAN MINERALOGIST

Ftc. 9. A projection of the gallobeudantite structue along [110], showing layers ofcomer-sharing Ga octahedra. The (AsO) tetrahedra (dark shading), (SO, tetrahedra(ight shading), and Pb atoms (filled circle) are aligued along [001].

ternary system as shown in Figure 10 ignoressymmetry and cell-dimension variations such asdoubling of the c axis. The boundary between Fe3+-dominant species (Frg. 10) and Al-dominant species(Fig. 12) is set at l:1; similarly, Ga-dominantspecies (Fig. 11) would have Ga > Fe3+ or Ga > Al,regardless of the sum of Feh + Al.

Solid solution

The A position in the fornula of the algnite -jarosite family may be filled by monovalent ions suchas K, Na, and (H3O), or by divalent ions such as Pb, Ba,Sr, and Ca. Figure 10 shows the nomenclature forthe (XO) temary system in which Pb is dominantin the A position and Fe3+ is dominant in B. The twopoints plotted correspond to gallian beudantite (up toL2.6 wlVo GqO3; Table 3). The analogous diagram,but with Ga > Fe3+, is shown in Figure 11.Compositions of gallobeudantite fall mainly along ornear the SOa - AsOa join, extending along its lowerhalf and into the field of the Ga analogue of segnitile

GALLOBET]DANTITE. A NEW MINERAL SPECIES, TSUMEB, NAMIBIA

P b . A Iunnamed(so+)z

L313

(Poa12plumbogummite

P b - F eplumbojarosite

(SOr),

(AsOo),segnitite

Hc. 10. Nomenclature for the Feh-dominant portion of flePb-XO4 members of the alunite - jarosite family. Plottedpoints 2.0 and 7.0 are compositions of Ga-rich beudantiteClable 3).

(PO.)" (AsO4)2

kintor6iie Phil iPsbornite

Fto. 12. Nomenclature for the Al-dominant portion of thePb-xO4 members of the alunite - jarosite family. Plottedpoints correspond to compositions in Table 3, but withXOa normalize Feh. Plotted points correspondto compositions in Tables 2 and 4, but with XOanormalized to 2.00. Gallobeudantite is the only namedmineral in the svstem.

@ig. 11, Table 2). In the opposite direction, the mostSOa-rich sample (cr3) is compositionally andmegascopically distinct, occurring on the specimen asa cream-colored isolated patch about a millimeter indiameter. The patch is a granular aggregate in whichthe grains are 5-10 pm across, are anhedral, brittle,and lack cleavage. In transmitted light, the grains arecolorless and uniaxial positive, with ro 1.786(5) ande 1.790(5) at 589 nm. Thus, the higher indices ofrefraction and change in optic sign distinguish thisphase from gallobeudantite, less rich in SOo and POa,but no differences were observed in the 114.6-mmX-ray powder-diffraction pattems of the two fypes.

Solid solution involving As-for-P substitution in thezoned crystals is minimal in areas that can be analyzedquantitatively with confidence. Thus, Figure 11 showsclustering of compositions either along the As-rich joinor the P-rich join, with no As - P intermediate values.The P-rich compositions correspond to the unnamedGa analogue of corkite and the unnamed Ga analogueof kintoreite.

Substitutions among Ga, Fe, and Al are extensiveoand any of these may predominate in B. Thus,compositions extend from gallian beudantite(Fe3i > Ga > Al), to gallobeudantite (Ga > Fe3+ > Al,

(Soa)2

t3t4

FerqAl.o,

T}IE CANADIAN MINERALOGIST

PbO, wt%CaO

TABLE 9. DLDCTRON-MICROPROBE COMPOSnONS oF c€-ca ARSENATE

4.1 6 2 3.1 1.2 Avg. Forntul4 I4O

G€O: 12.4 ll.7 12,0

2.42 Pb 0.07 , ""8.40 ca 0-97 's

12.16 Ce 0.7523.70 Gal.A --3.30 Fe 0.27 L>t

2,44 A 0.31

GarO, 23.5 22.4 23.82.4 5.0 3.13.0 2.5 2.6

and Ga > Al > Fe3+), to gallian hidalgoite (Al > Ga >Fer+; Fig. 12).

In gallobeudantite and its associated minerals, theA position is occupied solely by Pb (Iables 2,3,4);however, some of tle crystals have a narrow outennostzone, invariably less than 10 prn wide, in which Capredominates in the A position. This mineral isunstable under the electron beam" and the narrownessof the zones and the instability make analyses dfficult.Nevertleless, the results (Iable 9) show a consistent

Ca-A lhuangite(so+)z

predominance in Ca and As, with Ga fte main elemgntin the B position. Contents of Ge are up to 12.7 wtvoGeOr (Iable 9); although some substitution for Aswould be expected on the basis of their similar ionicradii (Bernstein 1985), it is evident that Ge# in thebeudantite-type minerals substitutes for the trivalentions in the B position. This Ca-rich mineral is inessence a Ca{a arsenate that, if Ge were absent,would correspond to the Ca analogue of the unnamedGa analogue of segnitite (Figs. 10, 11) or, more simply,to the Ga analogue of arsenocrandallite (Fig. 13). Theideal end-member formula of the latter catr be writtenas ̂ CaGa3H(AsOr2(OH)6. Substitution of Gea forGar+ is substantial, but is constrained by charge-balance limits so that the maximum Ge contentprobably corresponds to Ca(Ga,Al,Fe)2Ge(AsO/2(OH)u. Table 9 shows that the composition of theTsumeb mineral reaches 75Vo of the probableallowable limit of Ge substitution.

ACIiNOWLEDGEN4EIITS

We thank CANMET personnel P. Carribre forassistance with the X-ray powder studieso andJ.M Greer for preparation of the polished sections.Dr. F.C. Hawthorne of the Department of GeologicalSciences, University of Manitoba, kindly arranged forthe use of the four-circle diffractometer. The criticalreviews and editorial comments by A.C. Roberts,W.D. Birch, A. Pring, and R.F. Martin are muchappreciated.

RnrnnnNcrs

BERNSTEnI, L.R. (1985): Germanium geochemistry andmineralogy. Geochim. Coyrnchim. Acta 49, 2409-2422.

(1986): Geology and mineralogy of the Apexgermanium-gallium mine, Washington County, Utah.U.S. Geol. Surv.. Bull. 1577.

BrRcH, W.D., PRsrc, A. & GArEHousE, B.M. (1992):Segnitite, PbFqH(AsO)2(OtI)e, a new mineral in thelusungite group from Broken Hil1, New South Wales,Australia. An. Mineral. 77. 656-659.

CowcrLL, V.M, HrncmlsoN, G.E. & JoEllstru, O. (1963): Anapparently triclinic dimorph of crandallite from a tropicalswamp sediment in El Pet6n, Guatemala. Am. MineraL S,lr4-1153.

Durnzec, J.E. (1984): The behaviour ef impurities duringjarosite formation. In Hydrometallurgical ProcessFundamentals @.G. Bautista, ed.). Plenum Publ. Co.,New Yorh N.Y. (125-169).

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2,6 2.87.7 8.5

12;7 t2.025.0 23.82,9 3.t1.5 2.6

19.0 37.10.7 0.702 0.0

92.3 90.6

2,88.5

t2.023.83.1

37,10,70.0

90.6

1.59.0

|.7

5.02.5

38.00.70.0

90.8

8.3

12.423.52.43.0

38.81.00.0

91.8

A A

5.18

As2.l4s 0.06P 0.00

38.000.760.04

91.22

Aqots03PrO,

(AsO4)2arsenocrandallite

(Poa)2crandallite

FIG. 13. Nomenclature for the Al-dominant portion ofthe Ca-XOa members of the alunite - jarosite family. Theequivalent Fe3* analogues are not known;

"omporitionsin Table 9 conespond to the Ga analogue of arseno-crandallite.

& - (1989): Beudartite: PbFe.(SOo)(AsO/(OH)6, its crystal structure, tetrahedral sitedisordering and scattered Pb distribution. Neues Jahrb.Mi neral. Monntsh., 27 -33.

Gmce, J.D., NrcKEL, E.H. & Gaulr, R.A. (1991):Ashburtonite. a new bicarbonat€-silicate mineral fromAshburton Downs, Western Australia: description andstructure determination. Am. Mineral. 76. 1701-1707.

Hoptm{s, J.L. (1985): Apex nine goes into production. C/MBull. 7E(879),86-87 .

Jeuron, J.L. & DurnIz^c, J.E. (1983): Beaverite -plumbojarosite solid solutions. Can. Mineral 2l,101-113.

Kovara*rm., V.A. & RoBRrs, A.C. (1995): Newmineral names. Am. Mineral.80. 630-635.

13 l 5

PRDIG, A., BIRcH, W.D., DAwE, J., TAYIoR, M., Ds.;rsNs, M.& WALENTA, K. (1995): Kintoreite, PbFe3(PO)t(OH,H2O)6, a new mineral of the jarosite - alunite family,and lusungite discredited. Mineral. Mag, 59, 143-148.

RADosLovIcH, E.W. (1982): Refinement of gorceixitestructure in Cm. Neues Jahrb. Mineral. Monatsh.,446464.

Scorr, K.M. (1987): Solid solution in, and classification of,gossan-derived members of the alunite - jarosite family,northwest Queensland, Australia. Am. Mineral. 72'178-1,87.

Srfl-DRIcK, G.M. (1990): SHELXTL, a CrystallographicComputing Parkage (revision 4.1). Siemens AnalyticalInstruments, Inc., Madison, Wisconsin.

SzyMAI(sK, J.T. (1988): The crystal structure of beudantite,Pb(Fe,Al)3[(As,S)O4]2(OH)6. Can Mineral' ?rt, 923-932.

GALLOBEUDAIVTITE, A NEW MINERAL SPECIES, TSUMEB, NAMIBIA

GruseppsTn, G. & Telnlt, C. (1987): Corkite, NovAK, F., Jft, J. & PRAcHAft, I. (1994): Classification andPbFq(SO/@OJ(OII)6, its crystal structure and ordered nomenclature of alunite - jarosite and related mineralarangement of the tenahedral catrons. Neues Jahrb. gjonps.V&tnik.eskgtogeol.tlstavu6g,5l-57.Mircral. Moratsh.7|-8L

PRrsEv, N.N. & Ronrnm, A.C. (1996): Newmineral narnes. Am. Mineral. 81, 249-254.

Nonrn, A.C.T., Hilr-ps, D.C. & Marrtsws, F.S. (1968): Asemi-empirical method of absorption coilwtior.. Acta Received November 21, 1995, revised manwcript acceptedCrystallogr. 424,351,-359. August 20, 1996.