823
Th.e Canndian M in eralo g ist Vol. 36, pp. 823-830(1998)
THECRYSTAL STRUCTURE OF DUGGANITE,PbrZn.Te*AszOtn
ANTTAE. LAM arvoLEE A. GROATI
Department of Earth and Ocean Sciences, University of British Columbia, Vancouveti British Colambia V6T 124
T. SCOT'TERCIT
Research Division, Canad.ian Mweum of Nature, Onawa, Ontario KIP 6P4
AssrRAst
Thecrystalstructueofdugganite,ideallyPbZnrTeeAs2O,a, a8.460(2),c5.206(2)A,VZZZ.AQ)A3,spacegroupP32l, Z = l,has been solved by direct methods and Patterson techniques, and refined to an R index of 2.7Vobased on 636 unique reflections measured using MoKcr radiation on an automated four-circle diffractometer. The structure consists of heteropolyhedral sheets of edge-sharing TeO6 octahedra and PbOs snub disphenoids, oriented parallel to (001). The sheets are cross-linked by AsOo and ZnOo tetrahedra, which share corners to form an interlinked, two- and three-connected two-rlimensional net parallel to (001 ). Cheremnykhite and kuksite are considered to be isostructural with dugganite, but with V and P respectively dominant at the As site.
Keywords: dugganite, crystal structure, telluate, asenate, lead.
Sovnuene
Nous avons afffui6 la structue cristalline de la dugganite, de formule id6ale PbrZn3TeeAqOrq, a 8.460(2), c 5.206Q) A, V 322.6(2) A3, groupe spatial P321,Z = L, par m€thodesdirectes et par techniques de Patterson,jusqu'l un r'sidl R de2.1Vo: cet affrnement a utilisd 636 r6flexions uniques mesur6es avec rayonnement MoKcr et un diffractomdtre automatis6 d quatre cercles. La structure contient des feuillets de h6tdropolybdres, plus pr6cis6ment des octabdres TeO6 I ar6tes partag6es et des disph6noides applatis PbOg,orient6s parallbles d (001). Ces fenillets sont interlids par des t6trabdresAsOo et ZnOa partageant des coins, pour former un r6seau d deux et trois noeuds en deux dimensions paralldle e (001). Nous consid6rons la cheremnykhite et la kuksite des min6raux isostructuraux, avec V et R respectivement, comme occupants du site As.
(Tladuif par la R6daction)
Keyw ords ; dugganite, 5x1g1urscrisral l in e, tellurate, arsenate,plomb.
Ivrnorucnou Te-oxysalt minerals in quartz or manganese oxide gangue material. At the dump of the Joe Shaft mine, Dugganitewas first describedby Williams(1978) dugganite was found with other Te-oxysalt minerals, from three mine dumps in the TombstoneDistrict, cerussite, emmonsite, and rodalquilarite. Cochise County, Arizona. The type material was Using Weissenberg and rotation photographs, discoveredat the Emeraldmine dump, occurringas Williams (1978) showed that dugganite is hexagonal, "spherulesof water-greenhexagonal prisms abundant "perhapso'P6lmmm. Cell dimensionswere refined from in a sugary,vuggy quartzmatrix". Numerouscrystals powder data;a 8.472(5), c 5.208(5) A. The average of dugganitewere discovered at this locality, associaled chemical composition (obtained using spectroscopic with parakhiniteand other Te-oxysalt minerals. At the techniques) was found to be PbO 55.3, CuO 1.2, ZnO Old Guardmine dump,crystals of khiniteare replaced 17.6, As2O5 10.4, TeO3 14.0, H2O (by the Penfield on the outside by a druse of minute crystals of method) 1.5, total IOO.Owt.Vo. Trace amounts of CO2, dugganite.Other mineralsfound at this site include Mo, Ag, and Cd also were detected. Additional (partial) chlorargyrite,chrysocoll4 quetzalcoatlite,and tenorite. analyses showed some substitution of Te for As. The At both the Emerald and Old Guard mine dumps, chemical formula suggested by Williams (1978) was crystals of dugganite were found associatedwith Pb.Zn3(TeO6),(AsOo)2-,(OH)u-r,,with .r in the range bromargyrite,chlorargyrite, and numerousunidentified O.94to 1.33.
I E-mail address: [email protected] 824
A mineralresembling dugganite was also described crocoite(PbMa). Mg, Fe, Co, andNi weresought, but by Kim et al. (1988) as a product of supergene not detected.Data were reducedusing a PAProutine oxidation in the Kuranakh deposit (central A-ldan, (programXMAQNT by C. Davidson,CSIRO). The Yakutia,Russia), where it is associatedwith calcite, analyticalresults are given in Table l, togetherwith cinnabar, gold, orpiment, altaite, clausthalite, thoseof Williams (1978)and Kim et al. (1988). descloizite,kuranakhite, naumannite, tiemannite, and yafsoanite.Single-crystal X-ray studiesshowed that the mineral is orthorhombic,with spacegroup Cmmm, TABLE 1. CHEMICALCOMPOSITION OF DUGGANITE Q22, C2mm"Cm2m or CmmL.Celldimensions were refined fro-m powder d,ata:a 8.57(3), b 14.84(5), Wlliams Kim et al. This stud}r+ c 5.21(3) A. The authorsnoted that X-ray data for (1e78). (1e88)t "normal"dugganite can also be indexedon this cell. r,vt.7o negligible - 0.24 The averagechemical composition (based on seven Pbo 6E2 51.47 53.13 electron-microprobeanalyses) was found to be (in wt.Vo)PbO 5L.47,ZnO 18.82,SiO2 0.96, P2O5 0.70, 1.2 0.00 1.06 V2Os3.61, As2O, 12.16, Sb2Os 0.07, TeO, 12.61, total ZnO 17.6 18.82 17.25 100.40.Note that this is zor the averagecomposition Al2o3 hAa abstractedrn Am.Mineral. (76, 1440,1991);that one wasbased on resultsof earlieranalyses obtained using sio, 0.96 1.06 differentstandards and a non-standarddata-reduction PzOs 0.70 4.90 routine.Recalculation on the basisof six Pb plus Zn atomsgave the formulaPb3Zn3Te(As,V,Si)2(O,OH)14. Vzos 3.61 0.03 Otler analogues of this mineral that contain AszOs 10.4 12.16 8.28 V + Si >> As, or with significantsubstitution of SbzOs v.ut P for As, were reportedbut not studiedin detail by l(Jmet aI. (1988). TeOa 14.O 12.61 13.48 I(jm et al. (1990) describedcheremnykhite and HzO iE kuksite,two new mineralsassociated with dugganite TOTAL 100.0 100.40 99.50 in the Kuranakhdeposit. The formulae, determined from results of electron-microprobeanalyseso were ^ ^2+ nsgligible 0.06 Pbln3TeOu(VOo),for cheremnykhiteand Pbln3TeO6(POa72 Pb2' 3.43 2.94 3.O4 for kuksite.X-ray-diffraction studies showed that both cu2* o.21 0.00 o.17 minerals are orthorhombic (Cmmm, C222, C2mm, Cm2morCmm2), with cell dimensionssimilarto those zn2. ?nn z.Yc 2.71 previously determinedfor dugganitefrom tle same nr? o.o2 deposit(Kim et al. 1.988).Their conclusionwas that cheremnykhite,kuksite anddugganite are isostructural. sio o.20 o.23 Dugganite has also been described from the rn$ n 1c 0.88 CentennialEureka mine dump in JuabCounry, Tintic 0.51 0.00 district, Utah, where it occurswith other secondary Cu-,Te-oxysaltminerals (Marty et al. 1993). 1.25 i?A o.92 The structureof dugganitewas solvedas part of SbF 0.01 project a long-term on the crystal chemistryof the noq Te-oxysaltminerals. 1.11 u.vz H- 2.31
E>eeRnmNTAr- 02- 14.2s 14.02 l2 0n
Electron-microprobeanalyses were obtained using Note: Oxides are in weight perc€nt; analysesare normalized on nine cations per formula unit. *Averageof four AAS aJEOL733electron microprobe with TracorNorthern analysesfor Pb, Cu, Zn, and three visiblespectroscopy 5500and 5600 automation. The wavelength-dispersion analysesfor Te. As (two analyses)by UV spectroscopy. mode was used. The operatingconditions were as Trace Cd, Ag, Mo, CO2. Water by the Penfieldmethod. follows: voltage15 kV, beamcurrent 20 nA, andbeam tAverage of seven electronmicroprobe analyses. {Average of six electron microprobeanalyses. diameter5 pm, Data for Si, P, Ca, As, and Te were collectedfor 25 s; data for all other elementswere collectedfor 50 s. The following standardswere used: almandine(Al/(a), zircon(SiKa), PbrTi(POo)u(PKa), The crystalused in this studyis from the 400-foot CaTaaOll(CaKa), VPrO, (VKa), cuprire (CuKcr), level of the Empire mine, nearTombstone, Arizona. willemite (ZnKa\ mimetite(AsZc), TeO,(TeIc), and It was examined with a petrographicmicroscope THE CRYSTALSTRUCTURE OF DUGGANITE 825
TABLE 2. MISCELLANEOUSINFORMAIlON: DUGGANnE for evidenceof nwinning;none was seen.The crystal a (A) 8.460(2) Radmono MoKq/gEphite was mountedon a SiemensP3 automatedfour-circle c s.2@(2) Total refleciions 3746 diffractometerequipped with a molybdenum-target v (A1 322.aQ) UnlquE refledions 636 X-ray tube (operatingat 55 kY 35 mA) and a precisely Spe€ grcup p?21 Rn(oh) 9.8 orientedgaphile-crystal monochromatormounted with z 3d.(41 558 z1 [/ equatorialgeometry. Fifty reflectionsin therange 7.83 Crystal size (mm) 0.1 x 0.08 x 0.05 R (oh) 2.7 to 45.69"20 werecentered using an automatedsearch F (Mor(e; mn'') 49.89 wR (o/o) 2.e routine,and the correctunit-cell was selected from an R = tlF^ -F-lltF^ arrayof real-spacevectors corresponding to potential unit-cell axes. Least-squaresrefinement of these wR= ltfr'TF- r-ll'rtw.r-'l*. -l w- r t-r '' reflections producedthe cell dimensionsgiven in
TABLE3. ATONiIICPARAMETERS FOR DUGGANITE
Site z Urr" Uz Us Un UB Uzs Uq Te0 0 305(6) 305(6) 158m153(3)00256(5) As 1E 213 0.s2e4(6) 237(11) 237(11) 36e(18)11e(s)00281(e) Pb o.5s472(9) 0 359(3) 380(4) 303(3) leo(2) 10(1) 20(3) 345(2) Zn 0.2&6(2) 0 1t2 343(8) 286(s) 248(s) 143(5) -7(4) -14(8) 2sen o(1) 0122(1) o.212(1) 0.217(2) 325(43) 363(48) 247(35) 10e(38) 43(32) -50(31) 33e(3s) o(2) 0.467(2) o.2oo(2) 0.339(2) 502(64) 671(77) 398(5e) 48(62) 178(4e) -77(531 632(56) o(3) 1t3 z3 0.23s(4) 4o7(5e) 4o7(5s) 668(123)203(30) o o 494$n
"Ut and U values are listed x 10o
TABLE 4. SELECTED INTEMToMIC DISTANCES (A) AND ANGLES E) FOR TABLE5, BONDVALENCE'ARRANGEMENTIN DUGGANITE DUGGANrTE T€ Total Te-O(1) 1.s25(8) o(1)b-Prc(1)i 65.s(3) O(1) 0.98(2),6J 0.&(1)'21 0.58(21'212.02(3)
Srnucrrrne SoLUTIoNAND REFDTEMENT
The SiemensSHELXTL PC systemof programs o(3) was usedthroughout this study.Scafiering curyes for neutral atoms together with anomalousdispersion coefficientswere taken from Cromer& Mann (1968) and (1970). Cromer & Liberman Miscellaneous Ftc. 1. Coordinationof the Pb atomin dugganite. informationconcerning the collectionand refinement of the dataare given in Table2. The meanvalue of tE - ll was found to be 0.65, which implies a non-centrosymmetricspace group. Both direct methodsand Pattersontechniques were volume is 9.43 A3. The electron-microprobedata, usedto solve the structure.The structurewas refined in refined site-occupancy,and bond-valenceanalysis P32l to an R index of 4.7Vofor an isotropicdisplace- confirrnthat the siteis completelyoccupied by Te&. ment model.Conversion to anisotropicdisplacement The atomat theAs site,special position ?l (t/t,zA,z), factorsfor all of the atomsin the structureresulted in is coordinatedby four O atomsforming ^adistorted convergenceat R and wR indices of 2.7 and 2.97o, tetrahedron.The As-O distancesare 1.64 A (x 3) and respectively(3.9 and lO.4Vof.or alt 636 data).Addition 1.51A (mean1.61 A), and the O-As-O anglesare of an isotropicextinction correction did not improve 103.8' and 1L4.7"(mean 109.3"). The bond-length the results.Positional coordinates and anisotropic and (A; Hawthorneet al.1989) andbond-angle distortion equivalentisotropic displacement factors are given in parametersare 0.0049 and 29.73, respectively.The Table 3. Interatomicdistances and anglesare given variancein the tetrahedronangle is 35.93,the mean in Table 4, and,a bond-valenceanalysis in Table 5. quadratic elongation of the tetrahedronis 1.0080, Structurefactors may be obtainedfrom the Depository and the polyhedronvolume is 2.11A3. The average of Unpublished Data, CISTI, National Research electron-microprobe-derivedcomposition indicates Council,Ottawa, Ontario KIA 0S2. thatthe As siteis occupiedby Ass*(45Vo),P5* (43Vo), Si4 (ll%o) andAl3* (l7o). Refinementof the siteoccu- DsscRmoN oF Tm SrRUcruRE pancyfor As and P shows54Q)qo As, 46(2)Vo P. T\e meanbond-valence @rese & O'Keeffe l99l) obtained Thereare four distinct cationsites in the structureof usingthese proportions is 5.2 valenceunits (vz). The dugganite.The atomat the Tesite, at specialposition bondvalence obtained using proportions derived from la (0,0,0),is coordinatedby six O atomsforming a theaverage electron-microprobe data is 5.0 vz, andthe slightly distortedoctahedron. The Te-O distancesare valuesfor the coordinatingO(2) and O(3) atomsare 1.925A, and the O-Te-O anglesrange from 85.5 to l.9l and2.02vu, respectively. 96.8" (mean90.2'). The Te-O distancesare similar to Theatom at thePb site,at specialposition 3e (x,0,0) thosepreviously described for leisingite(1922 A; is coordinatedby eight O atomsoforming a distorted Margisonet al. 1997),jensenire (1-936 A; Gice et al. snubdisphenoid (Johnson 1965)^(Fie. l). The Pb-O 1996),frankhawthorneite (1.939 A; Grice & Roberts distancesrange from 2.40to 3.00A (mean2.74A), and 1995), parakhiwte_(1.92 A; Burns et al. 1995), theO-Pb-O anglesvary from 65.9oto-133.0" (mean yafsoanite(1.929 A; Jarosch&Zemann 1989),and 91.5').The polyhedralvolume is 34.40A3. The Pb site carlfriesite(1.933 A; Effenbergeret al. L978).T"he is almostcompletely occupied by Pb2*,although the bond-angledistortion parameter (oz;Hawthome et al. electron-microproberesults suggest a smallamount of 1989)is 16.9.The variancein tlre octahedronangle is substitution(2%o)by Caz+.Pbz+ is commonlylone-pair 18.45,the mean quadratic elongation of theoctahedron stereoactive,which typically resultsin a very asym- (Robinsonet al. 1971,)is 1.0053,and the polyhedral metrical (one-sided)coordination, with the lone pair THE CRYSTAL STRUCTURE OF DUGGANITE 827
l- a.--/ Frc. 2a. The heteropolyhedral sheet in the dugganite structure, projected onto (001). The TeO6 octahedra are indicated by a regular dot pattern, and the PbOs polyhedra, by a random dot pattern. Polyhedron "a" is in the same orientation as in Figure 1.
of electronspositioned on theopposite side of theatom edges,each with a different PbOspolyhedron; the to the coordinatingani6ns. However, the coordination lengthof the sharededges is 2.61 A. As expected,this of Pb2*in dugganiteis relatively symmetrical,and is shorterthan the unsharededges of the octahedron difference-Fouriermaps show no evidenceof a lone Q.7OAx 6 and2.88 A x 3). Eich PbO,polyhedron pair of electrons. sharesone edge with aTeO6octahedrono one edge with The atom atthe Zn site,special position 3f (x,O,lt), an AsOatetrahedron (length 2.58 A), and four edges is coordinatedby four O atomsforming a distorted with four otherPbO6 polyhedra. The lengthof the latler tetrahedron.T\e Zn-O distancesrange from 1.91to edgesis 3.36 A, which is shorter than the mean 1.97A (mean1.94 A); theseare similar to thelalZn-O (3.87A) of the 12 unsharededges (3.04, 3.34,3.47, length (1.97 A) calculatedusing ionic radii from 4.10,4.59,and 4.65 A, all x 2). Shannon(1976). The O-Zn4 anglesrange from 101.5 The AsOo and ZnOa tetraledra sharecorners to to 129.8' (mean 109.70).There are two additional form an interlinked, two- and three-connectedtwo- O(l) atomsat distancesof 2.90A; it is unlikelythat dimensionalner parallel to (001)(Fig. 2b). The two they form bondswith the atomat theZn position.The AsO4 tetrahedrain each unit cell point in opposite bond-lengthand bond-angle distortion parameters are directions,with apical O(3) atomsoriented * z. The 0.00096and 112.38,respectively. The tetrahedron three basalO(2) atomsare sharedwith different ZnOa anglevariance is 135.30,the mean quadratic elongation tetrahedra.EachZnOo tetrahedron shares two corners of thetetrahedron is 1.0363,and the polyhedral vol 'me witl AsOa tetrahedra.The rattrer complex Schl[fli is 3.55 43. TheZn site is almostcompietely occupied symbol(O'Keeffe & Hyde 1980)for the resultingnet by Znz*. The averageelectron-microprobe results is (122.123)6.It is interestingto note that if the TeOu suggesta minor amount(67o) of substitutionby Cu2*, octahedraare considered as part of the net, the resultant althoughCu2* does not commonly occur in tetrahedral Schliifli symbolis the muchmore conventional 63. coordination(Eby & Hawthorne1993). The TeO6octahedra and PbO6polyhedra share The sheetsof heteropolyhedraare linked by AsO, edgesto form a sheetof heteropolyhedraparallel to andZnOa tetrahedra (Fig. 3). EachAsOa tetrahedron (001) (Fig.2a).Each TeO6octahedron shares three sharesan apicalO(3) atomwith threePbOr polyhedra, 828
r a2
F a,___/
FIc. 2b. The layer of tetraledra in the dugganite struc$re, projected onto (001). The AsOn tetrahedra are shaded with crosses, and theZl'Oo tetrahedra are ruled.
T c _L
F'rc. 3. The dugganitestructure projected onto (100). The shadingis the sameas in Figure2 (with Pb atomsas spheres).
and three basal As-O(2) edges (2.58 A) with three corners with two TeO6 octahedra in different sheets, PbO6 polyhedra in a different sheet. The AsOa and TeO6 and four corners with six different PbOr polyhedra. The polyhedra have no anions in common and tlus are not sheets of heteropolyhedra and layers of tetrahedra directly joined. Each ZnOo tetrahedron shares two alternate along c to form the three-dimensional structure. 829
DtscusstoN Bunns, P.C., CoopER,M.A. & HAwTHoRNE,F.C. (1995): Parakhinite, Cu2*3PbTeeO6(OH)2:crystal structure and The idealformula of dugganiteis Pb3Zn3TeAsrO,o. revision of chemical formula. Can. Mineral, 33,3340. The electronmicroprobe and bond-valenceanalyses CnoLfiR" D.T. & Lnm.val, D. (1970): Relativistic calculation imply that there is little to no OH or H2O in the of anomalous scattering factors for X rays. J. Chem. Phys. structure.The empiricalformula, based on the average 53.1891-r898. resultsof theelectron-microprobe analyses, and calcu- lated on the basisof nine cationsper formula unit, is & MANN,J.B. (1968): X-ray scatteringfactors (Pb3 computedfrom numericalHartree-Fock wave functions. eoCa666)p. .ro(Zn .r rCuo.r1)12.ssTee.e6(Ase.e2P0.88Si0.23 -324. Ab.0t>2.05or3.e0,This is similarto theformula based on Acta Cry s tallo g r. AA, 321 the structure analysis, which is Pb3Zn3Te(As,.u,Env, R.K. & HawrHonNs,F.C. (1993): Strucnral relations in Po.st>.00o,0.The empiricalformulae calculated from copper oxysalt minerals.I. Structural hierarchy.Acta the analysesin Mlliams (1978)and lGm et aI. (1988) CrystallogrB,49,28-56. (on the basis of nine cations per formula unit) arc Pb t.*(Ztt66Cu6.21)p.21Te,.,, As,.25O,,.eoOH2.3 I and EFFENBERGER,H., Zrvarw, J. & Mavrn, H. (1978): Pb2.eoZnr.r5Te6.e2(As S io.20Po.l3Sb0.0 Carlfriesite: crystal structure, revision of chemical 1.35Ve.5I r)>z.zoOro.or, -852. respectively. Note that in each study, As is the dominant formula,and synthesis. Am. Mineral. 63, 847 cationin theAs position. As notedabove, minerals with Gnrcn,J.D., Gnoar, L.A. & RoBERrs,A.C. (1996):Jensenite, V (cheremnykhite)and P (kuksite)dominant at theAs a cupric tellurate framework structure with two site havebeen described by Kim et al. (1990),and are coordinationsof copper.Can. Mineral.34, 55-59. presumedto be isostructuralwith dugganite. & RoBERrs,A.C. (1995): Frankhawthorneite,a Km et al. (1988,1990) chose an orthorhombicrnit- unique HCP framework structureof a cupric telluate. cell(a - 8.6,b - 1.4.8,c - 5.2 A; for all thleeminerals, CavuM ineral. 33, 649-653. and suggestedCmmm, C222, C2mm,Cm2tn or CmmZ (1989): aspossible space-groups. The orthorhombiccell canbe FlawrnonNn,F.C., Gnoer, L.A. & Esv, R.K. Antlerite, heteropolyhe&alwallpaper structue. derivedfrom a hexagonalunit-cell CurSOo(OH)4,a by using the formula Can. M ineral 27. 205-2O9. bo6= Zay".cos30o. However, it wouldonly be necessary to use this cell if there were ordering, e.g., of As JARoscH,D. & Zeuerw, J. (1989):Yafsoanite: a garnettype betweenpseudo-equivalentAs positions, and there is no calcium- tellurium (VI) - zinc ortde. Mineral. Petrol. 40, evidence for this. In addition, the space groups 1,1,1,-t16. proposedby Kim et al. (1988, 1990) are neither subgroupsor supergroupsofP321. Without studying JoHNsoN,N.W. (1965):Convex polyhedra with regularfaces. the samplesdescribed by Kim et al. (1988,1990), we Can. J. Math. 18, 169-200. suggestthat dugganite, cheremnykhite and kuksite are isostructural,and crystallizein tle hexagonalsystem KrM, A.A., ZAvAKIIA, N.V., LAvREl.tr'rv, Yu.G. & with spacegroup P321. Marcrorro, V.F. (1988): Vanadiansilician variety of dugganite- the first find in the USSR.Mineral. Zh. 6, 85-89(in Russ.). AcrNowreocewxrs & Marulorro, V.F.(1990): Kuksite The authorsthank William Pinchfor providingthe Pbln3TeO6@Oa)2and cheremnykhite Pbln3TeOo(VOo/z beautiful samplesof dugganite.We also thank Mati - new telluratesfrom the Kuranakhgold deposit(central Raudseppfor theinitial electron-microprobeanalyses, Aldan, southernYakutia). Zap. Vses.Minzral. Obshchest. (in and Maya Kopylova for translationsof the Russian 119,50-57 Russ.). references.Special 1fianks go to JoelGrice for his help (1997): with this and other studies. The manuscript was MARGrsoN,S.M., Gnucn,J.D. & Gnoer,L.A. The structure of leisingite, (Cuh,Mg,Zn)z(Mg,Fe) improved by comments crystal from two anonymous TetuOu.611r6.Can. Mineral. 35, 759-7 63. reviewers. Financial support was provided by the Natural Sciencesand EngineeringResearch Council of Marry, J.,Jwsnr, M.C. & RosERrs,A.C. (1993):Minerals of Canadain the form of a ResearchGrant to LAG, and the CentennialEureka mine, Tintic District" Eureka,Utah. through equipment grants from the B.C. Science Rocl Bnrsr, N.E. & O'Krannn, M. (1991): Bond-valence O'KrenrB,M.O. & Hvnn, B.G. (1980):Plane nets in crystal parametersfor solids.Acla Crystallogr.B,47,192-197 . chemistry.PhiI. Trans.R. Soc.Inndon 295A 553-618. " 830 THECANADIANMTNERALocIsT RonnrsoN, K., Gnus, G.V. & Rsss, P.H. (1971): Quadratic WtruAMs, S.A. (1978): Khinite, parakhinite, and dugganite, elongation: a quantitative measure of distortion in tlree new tellurates from Tombstone, Anzona. Am. coordinationpolyhedra.SciencelT2,56T-570. Mineral.63,1016-1019. SHANNoN,R.D. (1976): Revised effective ionic radii and systematic studies of interatonic distances in halides Receiyed December 16, 1997, revlsed manuscript accepted and chalcogenides.Acta Crystallogn A32,75I-'16'1. April 21, 1998