6t3 Conadian Mineralogist Vol. 30, pp. 613-631(1992) THE WODGINITEGROUP. II. CRYSTALCHEMISTRY T. SCOTTERCIT', PETREERNf ANDFRANK C. HAWTHORNE Department of Geological Sciences,University of Manitoba, Winnipeg, Manitoba R3T 2N2 CATHERINE A. MCCAMMON2 Department of Physics, University of Manitoba, Winnipeg, Manitoba R3T 2N2 ABSTRACT The wodginite group of minerals has been studied by electronmicroprobe, X-ray powder diffractometry, X-ray single-crystalmethods, Mcissbauer spectroscopy and atomic absgrption spectroscopy.Ideal wodginite is MnSnTa2O6; however, wodginite also can host major amounts of Fe2+, Fd*, Ti, M and Li, and minor to trace amounts of Snz+, Zr, Sc, W and Ca. Vacanciesoccur at the.4 (Mn) site and seemlikely for the I (Sn) site. Three homovalent and four heterovalentmechanisms of substitution dominatewodginite chemistry,resulting in the four known species of the wodginite group plus syntheticMn2Fe3+Ta5Ol5, which is not yet recognizedas a natural species.A procedure for the calculationof formulae has beendeveloped for electron-rnicroprobedata; it permits calculationof Li contents and the Fe2+:Fe3+ratio. There is a strong correlation betweenstructural and compositionalproperties of ordered membersof the wodginite group. By multiple regressionmethods, a seriesof equationshave been developedfor the calculation of unit-cell parametersfrom compositional data for ordered members of the wodginite group; these equationsgive unit-cell parameterswith root-mean-squareerrors averaging0.007 A on cell edgesand 0.04o on the B angle. Natural membersof the wodginite group are commonly partiany disordered.The B angle, cell volume and the ratio I(021)/1Q20)are most sensitiveto cation order. An index of order has been derived by comparing measured and calculatedI angles,and it givesthe degreeof order to within 590. Keywords:wodginite group, order-disorder, crystal chemistry,tantalum. SoMMAIRE Nous avons 6tudi6 les min6raux du groupe de la wodginite par microsonde6lectronique, diffraction X (m6thode despoudres et sur cristauxuniques), spectroscopie de Mrissbaueret spectroscopiepar absorptionatomique. La formule id6ale de la wodginite est MnSnTa2Os;toutefois, la wodginite acceptecour:rmment des proportions imponantes de Fd+, Fd+, Ti, Nb et Li, et des quantitdsmoindres de Sn2+, Zr, Sc, W et Ca. Des lacunespeuvent aussi impliquer la position.4 (Mn), et semblentprobables dans la position B (Sn). Trois m€canismesde substitution homovalenteet quatre de substitutionh6t6rovalente r6gissent le champ de compositionde la wodginite, et m&nentaux quatre espdces connuesdans ce groupe, en plus de Mn2Fe3+Ta5O15,,eui n'a toujours pas 6t6 trouv6 dans la nature. Nous ddcrivons un protocole de calcul de la formule pour les compositionsd6termin6es d la microsonde6lectronique, afin d'obtenir la teneur en Li et le rapport Fez+:Fe3*. Il existe une forte corrdlation entre les propri6tds structurales et compositionnellesdes membres ordonn€s du groupe de la wodginite. Nous nous sommesservis de rdgressionmultiple pour obtenir une s6ried'dquations visant d calculerles parambtresr6ticulaires i partir de donndessur la composition des membresordonn€s du groupe. Ces €quationsp.r.itt.tt de calculer les parambtresavec des erreurs'de0.007 A et 0.04osur lesdimensions et I'angleB, respectivement.Les membresnaturels de cegroupe montrent assezcouramment un d6sordrepartiel. L'angle B, le volume de la maille et le rapport I(O2L)/I(220)sont les plus sensiblesau degrd d'ordre cationique.Un indice du degr6d'ordre, bon i 590 prbs, ddcoulede la diffdrencedans les angles0 mesur6et calcul6. (Traduit par la R6daction) Mots-cl4s:groupe de la wodginite, ordre-ddsordre,chimie cristalline,tantale. rPresentaddress: Mineral SciencesSection, Canadian Museum of Nature, Ottawa, Ontario KIP 6P4. 2Presentaddress: Bayerisches Geoinstitut, Universit?itBayreuth, Postfach l0l25l, 8580Bayreuth, Germany. Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/30/3/613/3420475/613.pdf by guest on 03 October 2021 6t4 THE CANADIAN MINERALOGIST INTRoDUCTIoN ture. Ixiolite is devoid of order of its cations; however, cations in the wodginite structure order Work on the chemistry of wodginite has into three distinct sites, causinga quadrupling of principally appeared in descriptive reports of its the unit-cell volume of the parent ixiolite sut'cell: occurrence;there are few studieswith the chemistry a* : ?-oi,b* : 2bi, c* = ci, where the subscripts of the mineral as a primary objective. Given past w and i stand for wodginite and ixiolite, respective- confusion regarding the crystal structure of the ly. This schemeof cation order resultsin the ideal : mineral, its now recognizedstatus as a group of formula ABC2O1, with Z 4 and spacegroup populated B, Sn, and minerals @rcit el al. 1992a),its economic value as A/c; ideallyA is by Mn, by an ore mineral of tantalum, and its relatively C by Ta (Fergusonet al, 1976).Owing to cation common occurrence (Table l), we decided to order, there are two chemically distinct types of examine the crystal chemistry of the wodginite ng-zag chains in the wodginite structure (Fig. l). group. One type consists of alternations of .,4 and B Coctahedra. Unlike studies of natural material, synthesis octahedra;the other consistssolely of given level in work has been directed toward understandingthe Only one type of chain occupiesany crystal chemistryof the group. Turnock (1966)was the closest-packedarray; this results in two types the first to synthesizewodginite; he showed that of layers in the structure, one with chains of C polyhedra, A B ferric iron plays a role similar to that of tin in the the other with chains sf ard polyhedra. of structure. Komkov (1970) grew tin-bearing A more complete discussion the wodginite group wodginitesimilar in chemistryto natural wodginig- structural crystallographyof the given (1992b). group minerals.Sidorenko et ql. (1974)showed that is in Ercit et al. syntheticwodginite could be nonstoichiometricby growing sampleswith variableSn:(Mn+Ta) ratios. EXPERIMENTAL Gatehouseet ql. (1976) showed that Li could be incorporatedinto the wodginite structure in major Most of the electron-microprobeanalyses were amounts.Komkov & Dubik (1983)proved Sn = done at the University of Manitoba using energy Ti isomorphisrnin syntheticwodginite. dispersion(ED); the main data-setwas augmented (WD) Ferguson et al. (1976) showed the wodginite slightly with wavelength-dispersion data structure to be derived from an ixiolite substruc- obtained at the CanadianMuseum of Nature. ED X-ray spectrawere obtained with a MAC 5 electron microprobe using a Kevex Micro-X 7000 spectrometer.Spectra were collected for 200 live TABLE1. LoCALITIES0F U0DCINITE-GRoIPI|INERALS secondswith an operating voltage of 15 kV and a Local l t)t Saeple Saoplo ilo. obtalnsd sample current of 5 nA (measuredon synthetic l. Alto do clz pegDatite, Brull Y A.15 fayalite), and were corrected for current and 2. Ankole, thanda Y A.17 3. Annle Clalm pe$natits, llanltoba Y AC2-79,A-3 voltage drift. Line overlaps, such as TaMd and 4. Bensonp€gioatlte, ZiEbabre tl TaMq on NbZa, SnZB on TiKcu, and MnKB on 5. Coo3aCounty, AlabaDa Y CX-l 6. Cross Lake, llanltoba Y Ct-l FeKa were dealt with by non-iterative techniques 7. EraJarvl pognatlte fleld, Fln]and tf 8. Greenbushsspegnstlte, lf. Australla I C8-l to -4 of spectral stripping involving library spectra of 9. H€rbbNo. 2 p€gEatlt€, Vlrglnla I H2-1 individual elementstaken from standardsused in 10. Kalbln Range,tSSR N ll. Kariblb, ilanlbla nc-l the analysis of wodginite. Manganotantalite 12. Kazakhstan, USSR KZ-l 13. Red Cmss Lak€, tlanltobs (MnKcr, TaMa), fayalite and chromite (FeKo), 14. Kola Penlnsula, USSR K0-l rutile and titanite (Tii(o), cassiterite (SnZcu), 15. Krasonlc€, l,loravla, Czechoslovakla cz-l 16. Lavra Jabutl, lllnas Gerals, Brazll LJ-l to -3 CaNb2O6(NbIa), Sc metal (ScKa), ZrO2 (ZrLa) 17. l'larble Bar. ll. Australla t{B-t (CaKcr)were Data 18. ltlt. llatther, I. Australla tst-l and microlite usedas standards. 19. iluhsnba River, Rranda A-26 were reduced with Kevex software using the 20. llanplng, Chlna cH-l 21. Odd lest peguatlt€, lilanltoba 0I-102 MAGIC V program (Colby 1980). WD X-ray 22. Peerlsss psgnatlte, 5. Dakota A-29,-30 analyses were done with a JEOL 733 electron 23. Eastern Sayan, USSR t{ 24. Serldozlnho, Paralba, Bfazll Y BP.I microprobe using Tracor Northern 5500 and 5600 25. Eastsm Slbarla, USSR N 26. Strlckland Quarry, Connectlcut Y sQ-l automation. The operating potential was 15 kV; a 27. Kohero. NaDlbia Y ovK-8 25 nA beam current was used. Data for standards 28. Sulula pegnatite, Tamola, F.lnland Y sK-l 29. Tabba labba, l. Auslralla Y TT.I were collected for 25 s or 0.2590 precision per 30. Tahara, Japan Y TJ.I 31. TancopegEatlt€, llanltoba Y (069-,StitP-, element, whichever was attained first. Data for TSE-sorlss) sampleswere collectedfor 50 s or 0.590 precision 32. Lorar Ianco poglatlte, Fanltoba Y 33. Tuscany, Italy N at the lo level, whicheverwas attained first. The 34. Transbalk8l rsglon, tSSR Y rl-l following standardswere used: NiTa2O6(TaMa), 35. Vlltanlml p€gmtlte, Flnland Y VII-T 36. Iodglna, l. Australla Y m-t MnNb2Ou (MnKo, NbZo), cassiterite(SnZo), 37. Ygllo*nlf€, NUT 1 YKF-soriss rutile (Ti/(a), almandine (FeKa), R.EE-bearing Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/30/3/613/3420475/613.pdf by guest on 03 October 2021 CRYSTAL CHEMISTRY OF THE WODGINITE GROUP 615 '\ \. t.' _\. ::.;2 Y FIc. l. The ideal structure of wodginite projectedalong X. Polyhedraof one level alongXare shownin solid rule; polyhedraof adjacentlevels are shownin broken rule. .A and B octahedraoccupy one level of the structure;their pattern of order is shown. C cationsoccupy the octahedrashown in broken rule. The octahedra sharecis-edges along Z, which produceso-PbO2-like zig-zagchains. glass (ScKcu),CoWOa CY,/Ma)and synthetic ZrO, tion data, exceptfor a few, very small samples,for (ZrLoi. Overlap between WMa and TaM$ was which either a conventional 114.6-mm-diameter manually correctedprior to data reduction. Data Gandolfi camera or a Nicolet R3m single-crystal reduction was done with a conventional ZAF diffractometer was used.