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The Crystal Structure of Tungsttte, Wo3.H2o Jan T. Szymanski

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The Crystal Structure of Tungsttte, Wo3.H2o Jan T. Szymanski Canodian Mineralogist VoL 22".pp. 681-688(1984) THE CRYSTALSTRUCTURE OF TUNGSTTTE,WO3.H2O JAN T. SZYMANSKI Mineral SciencesLaboratories, CANMET, Departmmt of Energ,, Mines & Resources, 555Booth Street,Ottawa, Ontario KIA ^Gt ANDREW C. ROBERTS GeologicalSuney of Canada,601 Booth Street,Ottawa, Ontorio KIA 1Eg ABsrRAcr lite and other primary minerals of tungsten. It has been found in small ilnounts at various localities The crystal structure of tungstite, WO,.grg, has been throughout the world, but apparently not in suffi- solved from single-crystal X-ray-diffractometer data col- cient quantity nor as crystals large enough for com- lected with MoKa radiation (248 unique reflections, 405 prehensivemineralogical study. Literature references observed),and has beenrefined to an R index of 4.3V0. to this mineral date back over 160years (Palacheer Tungstite is orthorhombiE,Pmnb (pnmo with bad), with ol. 194), including studies by (1908) a 5.249,b l0.7ll, c 5.133A, Z:4. Thestructure is charac- Walker and Kerr (1944), terized by distorted octahedral units of tungsten atoms co- & Young but only recently have crys- ordinated by five oxygen atoms and a water molecule: the tallographic unit-cell parameters,possible space- octahedrashare four cornersin the equatorialplane to form group and a fully indexed X-ray powder-diffraction sheets. The structure is very similal to that found in pattern been reported (Roberts l98l). Sahama MoOy2H2O (Krebs 1972).The sheetsare held together by (1981),in his review of secondarytungsten minerals, hydrogen-bondingbetween the water moleculeand the oxy- concluded: a mineral speciestungstite is gen "As still atom in the axial position in the adjacent layer. The inadequatelydescribed and needsto be studiedwith W-O bond lengths are 1.69(2) Iaxiall, 2 x 1.83(3), modern laboratory techniques." Since crystalline 2 x 1.93(3)lequatorial] afi2.34(2) A waterl. Tne t*iut, massesof tungstite from the Kootenay Belle published powder-pattern for tungstite is corrected and mine, indexed. Salmo, B.C. are available (National Mineral Collec- tion of Canada, SystematicReference Series, Geo- Keywords: tungstite, aquatungsten(Vl) oxide, crystal- logical Survey of Canada, specimennumber 16549), structure determination, corrected powder-pattern. the crystal-structure analysis of this somewhat enig- matic mineral was undertaken as part of a study of SOtvttr{aIRS the mineralsof that region. Prior to this study, the only crystallographic information available was that grislailins On 6tablit la structure de la tungstite, tungstite probably is orthorhombic on the basisof WO3.HrQ, partir d de donn€esde diffraction X obtinues its optical properties (Sahamal98l), sur monocristal but eventhe en rayonnementMoKa e48 riflexions uni- publishedpowder-pattern (PDF ques,405 observ€es)affinement jusqu'au 18-1418)was unin- r€sidu R de 4.390. dexed. La tungstite est orthorhombiqte lmnb (pnma avecbad), aveca 5.249,b l0.7ll, c 5.133A et Z = 4. La strucrure contient des octaddres d6form6s d'atomes de tungst&ne coordonn6spar cinq atomesd'oxyg&ne et une moldcule CovposrnoN d'eau; chaqueoctaCdre parlage quatressommets dans le plan dquatorial pour former des feuillets. La structure res- The mineral specimenfrom which the crystalsfor semblebeaucoup d celle du MoOr.!!1r6 (IGebs 1972).Les structure analysis were extracted consists of a fine- feuillets sont reliespar desliaisons hydrogbneentre la mol6- grained intergrowth of tungstite and ferritungstite. cule d'eau et l'atome d'oxygbne en position axiale dans le It is not possible to isolate from it enough pure feuillet adjacent. Les longueurs des liaisons W-O sonr material for a microprobe analysis, or for a bulk 1.69(2)[positionaxi+], 2x 1.83(3), 2x 1.93(3) [plan analysisfor HrO. However, our powder-diffraction equatoriall et2.34(2)A [positionaxiale, eau]. Le clichdde poudre de la tungstite est corrigd et index6. data fit syntheticWO3.H2O (PDF 18-1418),and the synthetic material has been extensively analyzed Mots-cbs: tungstite, oryde de tungstbne(Vl)hydrat6, d6ter- (Freedman1959, Freedman & Leber 1964).Natural mination de la structure cristalline, correction du cl! material from various sources,identifed as tungstite ch6 de poudre. by the powder pattern (Kerr & Young 1944),has also been analyzed and found to agreewith the formula INTRoDUCTIoN WOr.Hrg. In the latter paper, the poorest agree- ment was found for tungstite from the Salno mine _ Tungstite, WO3. H2O, is a secondary mineral, (analysisof Walker 1908),the major lmpurity being fbrmed as an oxidation product of wolframite, schee- formulated as FqO3 and FeO. This is consistent 681 682 THE CANADIAN MINERALOCIST TABLE1. CRYSTAIDATA X-ray diffractometer, and precisecell-dimensions and orientation matrix were determined from the Tungstlte: f,Os.H20 source: KootenayBelle nlne' salmo, Brltlsh columbia. least-squaresrefinement of the observed%),x,6 and (Natlonal Mlneral collectlon of canada,systemtic ReferenceSerles, 0slogical Surveyof Canada, orvalues of 59 reflectionsin the range20' .20 < 34" SpeclnenN0. 16549). using MoKa radiation = 0.71073 A) (Busine Fomula l{elght: 249.86 O Crystal system: 0rthorhonblc, 7 - 4. 1970).At this stage,although it was apparentthat Systemtic absences:L&2, Oenerally present' the spacegroup was ot(Z' generally Present' the crystalsare orthorhombic, h0!'h+L"?n+f still uncertain. t&0, k _ 24+7 spacegroup: P@b (062, Poa cllh bdi). A positive octant of reciprocal spacewas defined celf dlmenslons:a = 5,249(2),b = 10.711(5)'a = 5.133(2)A. spots was best, Denslty: 0""]"-5.75 l,lgm-3, Dobsrct neasured,but Ualker (1908) where the shapeof the diffraction glves 5.517 for tungstlte fron the sane locallty, the lou and one octant of data was collected three times to value probably causedby lntergrorth with ferrltungstlte, of 20 = 72o using monochromated (Dobs=5.02 l,,lgn-3). a maximum radiation. All reflectionswithin this 20limil Absorptlon: u(Moeo)- 406.9 m-l MoKa Intenslty Data, one octant of, data collsted with l4ofdradlatlon were measured without reference to systematic to 20-72"t neasuredthree tlnes and averaged: o/min 748unlque reflectlons,405 wlth I > 1.65xo(I). absences.A scanrate of I was usedwith a base peak-widthof 2.1" , increasingwith dispersion(0.69 tand). Background counts were measuredfor 80 with the above descriptionof the mineralogy, and secondson either side of the peak. Three standard with our premiseabout the impossibility of doing reflections were monitored in order to check crystal precise analysis on material from the Salmo mine alignment and instrument stability. No systematic becauseof the intergrowth with ferritungstite. Thus variation was observed, and the minor variations it seemed necessary and justifiable, initially, to were ignored. Absorption corrections were applied assumea formula WOr,Hrg for the single crystals using a Gaussian integration procedure (Gabe & of the natural material, and to check the final O'Byrne 1970)and a erid of l0 x 10 x 10points. The difference-synthesisfor evidence of compositional correctionfactors varied between 1.85 and 7.05.The differences. No significant peaks were found at the three segmentsof data were averaged and reduced end of the refinement; though this doesnot preclude to structure amplitudes with the application of possibleminor substitution for tungsten, no such Lorentz and polarization corrections. Reflections substitution has been reported in the literature. were consideredas "observed" on the criterion that Iobs> 1.65 x o(I), where o(I) is obtained from ExPERIMENTAL counting statistics. Numerous crystalline fragments of tungstite were SvsrsMAtrc AsspNcss AND SPAcEGRoUP extractedfrom mineral specimen16549. Of these, only two very small crystalsshowed no grossevidence The lattice is primitive, with reflections hkl gen' of twinning, and both were used for extensive erally present; reflections Okl are generally present, preliminary precession-photo$aphy.Exposures of although reflections not obeying the/-centring con- up to 200 hours were used in order to try to observe dttion (hkl, k + I = 2n'1are very weak. Reflections the weak reflections from thesevery small crystals' h\l were observedonly for h = 2n and I : 2n, with and henceto differentiate weak reflections from sys- the exceptionof the (102)reflection, which appeared tematically absentreflections, so €tsto determinethe to be presentbut weak, and reflections (104) and possiblespace-group. (10O, which were at the extreme limit of observa- It was apparent from the preliminary work that bility on the 1.65 o(I) criterion. Reflections hlfi ate crystals of tungstite belong to the orthorhombic sys- present for k = 2n. The above absencesindicate tem, with the dimensionsquoted in Table 1. The spacegloup Pmcb or P2rb. However, the Patterson larger of the two crystals is a flat hexagonal tablet, function and the vector map (E2-1) could not be whose faceswere indexed from the precessionwork. interpreted on the basis of thesespace groups. The crystalis 53 pm between(100) and (100),61 pm Finally, a CAD4 diffractometer was used to col- between(101) and (T01),66 pm between(101) and lect a new data-set (MoKcr radiation, hemisphereof (101)and about 9 pm between(010) and (010).The data with k positive, all reflections collected to spotsobtained on the precessionphotographs from 20 - 60'). It was found that none ofthe four reflec- this crystal show minor splitting in certain regions tions of the {102}, {lM}, {106} forms wereobserved of reciprocalspace and somedisplaced "tails", but in this seconddata-set. In the latter, the "FLAT"
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