Canadian Mineralogist Vol. 14 pp. 5tl&549 (1976) THE GRYSTALSTRUGTURES OF TANTALITE,IXIOLITE AND WODGINITEFNOM BERNICLAKE, MANITOBA I. TANTALITEAND IXIOLITE J. D. GRICE*, R. B. FERGUSON AND F. C. HAWTHORNE Deparlment ol Earth Sciences,UniversiA of Manitoba, Winnipeg, Manitoba R3T 2N2 Assra.ec"r B(Ta)-0, 2.01(3)& e[es concordent chacung avec la somme des rayons ionrques, 2.19 et 2.fi)4, res- The crystal structures of matrganotantalite and pectivement. La somme des valences de liaison ixiolite from the Tanco pegmatite, Bernic Lake, (Pauling) qui aboutissent aux atomes d'oxyglne Manitoba have been refined using MoKo radiation O(l), O(2) et O(3) est peu pr6cise (2, lVz 2Yz u.v., and 3-dimensional 4-circle diffractometer data to respectivement), mais lorsqu'on ti€nt compte de la final R. values of 8.4Vo atd 8.97o respectiveb. distorsion des longueurs dans l'octaBdre (celui de B Tantalite:orthorbonhie Pbcn, a |4.4L3(3),, 5.760(I), en particulier) en consid6rant la valence de liaison c 5.0s4(1)4, Z-4\ABrosl-4[(Mne.r7Tin.62Fe!+q.s1 comme inversement proportionnelle I la 5" puis- Sne.6)(fa6.sNbo."")rOul. The structure of Stur- sance de la distance cation-oxygdne (Pyatenko 1973), divant (1930) is confirmed. The mean octahedral les atomes d'oxygdne regoivent 2.04, 1.99 et 1.97 l(MnlO distance is 2.18(4) and BCIa)-O is u.v., respectivement. 2.01(3)A, both in close agreement with the rele- L'ixiolite est orthorhombique Pbcn, a 4.785(2) va[t radii sums, 2,19 and 2.00A respectively. Paul- (-%a^".), b 5.758(2), c 5.160(2)A, Z- \(lao.s ing bond strengths to tle three oxygens O(1), O(2) Mn6.s6Nb6.22Tis.esSns.6s5Fe2+e.oor)Or].Sa structure est and O(3) are very poor (2, lVz, 2ty'z v.u.)" but celle d'une tantalite i cations d6sordonn6s avec tous when account is taken of the distance-distortion of les m6taux dans une m€me position sp$ciale 4M the octahedra (especially B) by distributing the et tout l'oxygdne en position g6n6rale 80. La struc- bond strengths inversely as the 5th power of the ture est du type c-PbO2. Crrtains 6l6ments de sy- cation-oxygen distance (Pyatenko 1973), the three m6trie de lixiolite correspondent, dans la tantalite, oxygens receive 2.04, t.99 arid 1.97 v.u. reE ectively. ir des 6l6ments de sym6trie vraie; d'autres, i des Ixiolite is orthorhombic Pbcn, a 4.785(2) 6l6ments de pseudo-sym6trie. La longueur moyeDne (-Vsat^".), b 5.758(2), c 5.160(2)A, Z-41(Ta6.oo des liaisons M-O, 2.06(4)4. concorde avec la som- Mn6.s6Nb62Jio.orSno.oo6Fen+o.ooJOrl.Th€ structure is me 2.O4it du rayon ionique de l'oxygine et de la that of a cation-disordered tantalite with all metals moyenne pond6r& des rayons cationiques. in one special site 4M and all oxygens in one gen- (Traduit par la R€daction) eral site 80. The structure type is c-PbO:. Some symmetry elements correspond to true, and others to pseudo-symmetry elements in tantalite. The DnotcetroN mean octahedral M-O distance is 2.06(4)4, in close It is a pleasure to include this pair of papers agreement with the sum oJ the oxygen and weigbted mean cation radii (2.044). on the structures of three tantalum oxide min- erals in the number of The Canadian Mineral- ogist dedicated to our colleague and friend, SoMMA.RB Leonard G. Berry, whose advice regarding cer- Les structures cristallines de la manganotantalite tain aspects of this work we gratefully acknowl- et de l'ixiolite ont 6t6 affin6es, sur sp6cimens prove- edge. nant de la pegmatite de Tanco, Bernic Lake, Mani- toba, i l'aide de donn6es tridimensionnelles obte- INrnopucttoN nues au rayonnement MoKo sur diffractomdtre i quatre cercles, jusqu'au r6sidu pond6r6 final R. de Tantalite, ixiolite and wodginite are three 8,4Vo eJ 8.97o respectivement. La tantalite est or- closely related orthorhombic or pseudo-ortho- tlorhombique Pbcn, a 14.413(3), b 5.760(7), c 5. rhombic tantalum oxide minerals, all of which 084( 1)A, Z* 4[A B 20;-4[(Mno.sTTio.oiFer*o.orSno.oor) occur in the Tanco pegmatite at Bernic Lake, Cfao.ual.Ibo.r")2Oul.La structure 6tablie par Sturdi- Manitoba. The prototype tantalite (columbite)' vant (1930) est confirm6e. La longueur moyenne des Iiaisons l(Mn)-O est 2.18(4) et ceUe des liaisons has the ideal formula FeTa:Ou(FeNbrOu); the general formula may be written as ,4BrOs where l=@ez+,Mn) and B=(Ia,Nb) with other ele- *Present address: Mineral SciencesDivision, Na- ments, particularly Sn and Ti, substituting in tional Museum of Natural Sciences,Ottawa, On- A and/or B. Upon heating, some ixiolites give tario, KIA 0M8. the X-ray powder pattern of olovotantalite 540 Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/14/4/540/3445819/540.pdf by guest on 30 September 2021 CRYSTAL STRUCTURES OF TANTALITE AND DqOLITE 54r (Nickel et al. l963a,b) or wodginite (Khvostova IXIOUTE & Maximova 1969) whereas others give the pat- tern of columbite-tantalite (Nickel et al. I963b). The latter authors suggested that only the firrt be regarded as true ixiolites, and they tentatively 'pseudo-ixiolite' ouggestedthe name for the sec- -WODGINITE ond. There appears to be distinct chemical dif- ferences between these two types, with ixiolite/ TANTALITE olovotantalite/wodginite generally s6ataining more Fe8+/Sn4+/Ti4+ than'pseudo-ixiolite'/ columbite-tantalite (Nickel et al. I963bi Cernf, pers. comm.). On the basis of cell dimensions, 'pseudo- Nickel et al, (1963a.b) proposed that ixiolite' is a cation-disordered columbite-tanta- lite with the general formula (A,B)zOa,or more Frc. 1. Relative unit cells of ixiolite (ar,bvc), tatta' simply (A,B)O,, and that wodginite is a mono- lite and wodginite. clinic pseudo-orthorhombic derivative of colum- bite-tantalite with the same simplest general points that may be made from Table formula as pseudo-ixiolite, (/4,8)Or. Gtiee et aI. following (1972) have described the detailed chemistry 1 and Figure 1: 'pseudo- the and crystal geometry of tantalite, (1) the setting used for tantalite in ixiolite' and wodginite from the Tanco peg- present study is that used by Strunz & Tenny- matite, confirming the proposals of Nickel er al. son (1970) ind Grice et al. (L972); this differs (1930) (1963a,b). As 'pseudo-ixiolite' has never been from the setting used by Sturdivant and approved as a valid speciesby the IMA Com- Nickel et al. (1963a); mission on New Minerals and Mineral Names, ((2) the true cell of tantalite llss a - L4'4, we use the name ixiolite throughout the rest of 6 -5,8, c -5.1A and a cell content of this paper. ABaO"n, but there exists a fairly distinct subcell Because different settings have been various- with d n4.g[-a/3, bt=b, C=c q4d a--ce!l r73(ABaOaa). $ ly used for tle cells of these minerals by differ- content o1 Although this ceII ent authors, Table 1 (modified from Grice er al. never used to describe tantalite, it is important 1972) summarizes this information. A back- as it correspondsto the true cell of ixiolite; ground to the present work is provided by the (3) Nickel et al. 0963b\ and Gice et al' (1972) respectively showed that ixiolite has a cell whose b allLde dimensions correspond to those of columbite-tantalite but whose a -4.8A n7/t a of tantalite; (1930) that in tle xThe tantalite/columbite cation-ordered structure (4) Sturdivant showed may be regarded as the prototype of these three structure of columbite-tantalite, the 4A cations minerals because it was the first to bo solved are in one site and the 88 cations in another (Sturdivant 1930); however, from a structural view- so that it is a cation-ordered structure; point, the cation-disordered structure of ixiolite (5) Nickel et al. (I963b) showed that in the and the same structure as with the smaller cell smaller ixiolile cell, there is only one site a-Pbor (see for example Wyckoff 1963, p. 259) all the sations; hence this minepl, should be regarded as the prototype. available for 'I. TABLE CRISTALLOGRAPH1CSETTINGS FOR IXIOLTIE' COIUItsITE/TNTALTTE'AND I{ODGINITE papeF papeF These These These PaFers & refs. & refs. ref. ref. true & refs. ref. refs .l.2.3.4a.5r 2,4b,5r 34a cell subcell 2.5,71 6 3.44 trus cglI subcell 'f4.4 (x1/3.)4.8 a(a'l b b(b' (xl12"14.8 a(q') Axlal 4.8 a ab (xl/2.)5.8 bb,) 5.8 b ba 5.85.8bda lengths,I 5.1 5.1 a 4 a 5.1 (eo) (e0) r9l " o9,t" (90) (rl/4.)139 iio'r,ls 140 423 (xl/3")l4l pb@ PMa P@r c2lo@2lo) Space gmup Pb@ or Col(or po) Ideal @ll ltalaav'a.R) content z (z')*{4,8,c)408 4Bs%z Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/14/4/540/3445819/540.pdf by guest on 30 September 2021 TTIE CANADIAN MINERALOGIST with cell contents (A,B)IO" must have a cation- as explained below. The cell dimensions given disordered structure. Such a structure is the in these tables differ slightly from those given same as a-PbO: (Wyckoff 1963, p. 259); previously because the latter are from refined (6) the cells of both tantalite and wodginite powder data for a relatively large amount of can be regarded as (different) supercells of material whereas the former are from single- ixiolite which may thus be taken as the proto- crystal diffractometer measurements on the type structure of ttrese three minerals.