THN AUERIcAN MINERALoGIST

IOURNAI OF THE MINERALOGICAL SOCIETY OF AMERICA

Vol. 48 SBPTBMBER-OCTOBER, 1963 Nos. 9 and 10

IXIOLITE-A SUBSTRUCTURE

E. H. Nrcxrr, J. F. Rowrenl and R. C. McAnalr, Mineral, Sciences Diaision, Mines Branch, Department of Mines and. Technical,Suraeys, Ottawa, Canad,o.

Ansrnecr

hiolite, first described in 1857 and mentioned in the literature only a few times since then, has generally been regarded as a discredited mineral species. A re-examination of samples from the type locality in Finland, however, has provided significant new informa- tion indicating that is a valid species with distinctive characteristics. X-ray dif- fraction studies show that ixiolite is orthorhombic with o:5.73, b:4.74 and c:5.164, space group Pcan. The unit-cell content is (Ta, Fe, sn, Nb, Mn)ros. The ixiolite unit-cell is a sub-cell of columbite, with similar parameters except for b, which is one-third of the columbite D parameter. structurally, ixiolite can be regarded as a disordered form of columbite.

INrnonucrron The mineral name ixiolite first appearedin 1857in a paper by Norden- skitild in which he describedtwo -like minerals from skogbiile in Kirnito, Finland. He regarded one of these as a relatively normal tanta- Iite, but the other, which was morphologically difierent and was ex- traordinarily high in manganeseand , he regardedas a separatespecies. This mineral, which was previously called ,,Kimito-tantalite,', was given the name ixiolite, from Ixion of Greek mythology. The name ixiolite has been given also to minerals from two other localities. one of these is in the rlmen Mountains in the Russian urals (Vernadsky and Fersman, 1910).Since there is no record of a complete chemical analysisnor of r-ray diffraction analysishaving been made, this occurrence cannot be considered authenticated. The other use of the name was made for a mineral found at Wodgina, Australia (Simpson, 1909),but this hasrecently beendiscredited (Nickel etol.,1963).r

CrownCopyright Reserved. I After completion of this paper, a new occurrence of ixiolite was reported from the Kalbin Ridge in the U.S.S.R. (V. A. Khvostova and N. V. Maximova, Dokl. Ahad.. Nauk S.S.S.R. 1963, 148, 424426; translation provided by M. Fleischer). However, evidently 961 E. H. NICREL. J. F. ROWLAND AND R. C. MCADAM

Amark (1941) and Quensel (1941) reviewed the status of ixiolite. Their work, which was based on a review of the literature as well as on r-ray powder diffraction studies on type material from Skogbiile, failed to substantiate ixiolite as a separatespecies. Quensel concluded that:

,,The name ixiolite, primarily defined by Nordenskiiild as representing a species of orthorhombic symmetry, consituting an isomorphous mixture of SnOz and Nb-Ta oxides, must for the present be regarded as problematic."

Mineralogical referenceworks, apparently drawing largely on the work of Amark and Quensel, have tended to treat ixiolite as a discredited species.Palache et at. (1944) and Hey (1962) conclude that ixiolite is probably identical with . Strunz (1957) states that ixiolite is probably a mixture of tantalite and .Ramdohr (1960)does not mention it at all. The authors becameinvolved in the ixiolite problem during an investi- gation of a tin-manganesetantalate from Bernic Lake, Manitoba' This mineral, subsequently characterizedas a new speciesand given the name (Nickel etal.,1963), was found to be very similar to the mineral from Wodgina, Australia, to which Simpson (1909) had given the name ixiolite. This led the authors to investigate the ixiolite from the type locality. Since this ixiolite was found to be distinct from other species,it was decided that the mineral should be redefined. The chemical analyseswere made by R. C. McAdam of the Analytical chemistry Subdivision. Responsibility for the remainder of the investiga- tion, including interpretation, was sharedby E. H. Nickel of the Mineral- ogy Section and J. F. Rowland of the Physical Chemistry Section'

Trnulworocv In this paper frequent refeience will be made to minerals of the colum- bite-tantalite group and, in view of the confusion surrounding the no- menclature of these minerals, the terminology employed here will be clarified. fn the mineralogical literature, minerals in the columbite- tantalite group are generally regarded as being orthorhombic and having a compositionexpressed by the formula (Fe,Mn)(Nb,Ta)2O6,with com- plete substitution of the catibns within the brackets. The names colum- bite and tantalite are given to members predominating in and

no samples of the type ixiolite were obtained for a direct comparison with the mineral from the new occurrence, and the single-crystal and power t+ay data reported arq not in com- plete agreement with our data on the skogbole ixiolite. No heating experiments were re- ported. ft is therefore questionable whether Khvostova and Maximova are justified in calling their mineral ixiolite. IXIOLITE 963

, respectively (Palache et at., 1944). Other names, such as ferrocolumbiteand manganotantalitehave been used to denoteiron- or manganese-richend-members, Minerals of the columbite-tantalite group, in addition to being re- garded as forming continuous compositional series, have also been re- gardedas isostructural.rn the light of the presentinvestigation and from recent literature reports, the authors do not consider this to have been proven. rn point of fact, there has only been one structural analysis of a mineral of the columbite-tantalitegroup (sturdivant, 1930),and this was done on a specimen that has not been chemically analyzed.,and whose composition is consequently uncertain. Sturdivant's structure has gen- erally been taken to apply to all members of the columbite-tantalite group. Recent evidence, however, strongly suggests the existence of crystallographic variants. Donnay and Donnay (1961), for exa-mple, noted significant differencesin morphology between members differing in Mn:Fe ratio, and Schrcjcke(1962) found MnNbzOo to have a unit cell twice the size of the one reported by sturdivant for his columbite- tantalite. Since a firm relationship between composition, crystallography, and structure has not yet been established,the authors will employ the term columbite-tantalite with referenceto those minerals having a composition expressedby (Fe,Mn)(Nb,Ta)rOo and producing *-ray difiraction pat_ terns corresponding to the mineral characterizedby sturdivant (1930). Following Sturdivant's usage, the structure will be referred to as the columbite structure.

GBltBnar, DB scnrprtoN Samples from the type locality at Skogbcile,Kimito, Finland were obtainedfrom collectionsat the Royal ontario Museum, the university of Helsinki and the Geological Survey of canada. All the sampreswere similar in appearance,consisting of different proportions of brack minerals and pink . A preliminary series of. r-ray powder diffraction pat- terns of the black grains in each of the samplesdemonstrated the pres- ence of two distinct mineral species-tapiolite and the mineral that will henceforth be designated as ixiolite. As shown in Table 1, the sample labels do not, in general,conform to the x.-rayidentifications, nor is there any consistent relationship between them. None of the powder patterns obtained represented more than one phase, which indicates the absenceof fine-grained intergrowths between the two minerals. Sample M-11894 contained eight black grains, four of which proved to be ixiolite and four tapiolite. The remaining samples appearedto contain either one mineral or the other, but not both. 964 L^ II. NICKEL, J. F. ROWI'AND AND R. C. MCADAM

Tnsln 1. IorNlmrca.troN or Srocsdr-r Saupms lv X-Rlv Powopn Drlrn.q.ctrox ANAI-YSrs

Mines Branch Source Sample Label Identification

(6) Royal Ontario Museum M-6591 Skogbdlite (: tapiolite) Ixiolite (4) Royal Ontario Museum M-11606 Tapiolite Tapiolite (4) Royal Ontario Museum M-11894 Ixiolite Tapiolite and Ixiolite (4) (4) Royal Ontario Museum M-146s3 Ixiolite Tapiolite (1) University of Helsinki tot+ Tapiolit (Tantalit) Ixiolite (1) University of Helsinki 1015 Tapiolit (Ixionolit) Tapiolite (1) Geological Survey of Canada x-3t[4 Ixiolite Tapiolite

(The number of *-ray powder difiraction patterns obtained from each sample is given in parentheses.)

Monpuor-ocv Most of the ixiolite in the samplesexamined occurs as irregular grains with no discerniblecrystal faces. sample M-6591, however, contained two relatively largeixiolite masses,one of which had three unevencrystal faces(Fig. 1b). Although the faceswere too irregular for accuratemeas- urement, approximate measurements of two interfacial angles could neverthelessbe made with a contact goniometer.The results (Table 2) agree,within the errors of measurement, with two of the anglesreported by Nordenskidld,and with valuesof 100A130 and 100A112 calculated

Frc. 1a. Crystal drawing of ixiolite, adapted from Nordenskidld's Figure 3, and re- oriented to conform to the setting used in this paper. Relationship to Nordenskidld's sym- bols are as follows:

Nordenskiiild ab cmtP This paper {010J {oo1} {100} {0121 {130} lrr2l IXIOLITE

Ttw.n,2. Iwmnlacral Alcrrs ol' Ixrolrrn Cnvsr.lr,s lnou Sxocncir-r,Frwr,axo

M-6591 Nordenskicild Calculated Indicesr (This paper) (18s7) Angles2

100n130 75" 74" 58', 71"35' 100n112 67" 68050', 68026', 100n110 51015/ 50"24' 110n112 54"46' 54047',

I Nordenskiiild's indices have been transformed to agree with the ixiolite unit cell parameters, as follows: h+k; k+l/2; l+h. 2 calculated values are derived from the following unit-cell parameters: a:5.731, b:4.742 and c=5.152 A (seeTable 3). from the unit-cell parameters determined by single-crystal r-ray diffrac- tion analysis.The other two anglesreported by Nordenskidld, but not observedby the authors,are also in good agreementwith the calculated angles.For this reason,and becauseof other evidencegiven later, the authors believe that sample M-6591 correspondsto the material origi- nally describedby Nordenskicildunder the name of ixiolite. Figures 1a and 1b show the relationship between one of the crystals describedby Nordenski

Frc. 1b. Photograph of iriolite crystal from sample M-6591, in approximately the same orientation as Fig. la. crystal faces (100), (130) and (112) are shown. Masnification approx. 3X. E. H. NICKEL, J. F. ROWLAND AND R. C.'MCADAM

Sprcrlrc Gnavrrv Nordenski

X-nav CnvsrerrocRAPHY Buerger precession photographs of ixiolite single crystals indicate orthorhombic symmetry, with space group D]fr. Rather than adopt the

Tlsm 3. UNrr-Cnr,r,Paneunrnns ol Ixror-rtn (ANosrnou UNr:rs)

Sample No.

M-6591 5.152 M-11894 5.163 conventionalsetting of the unit cell (c1a(b), a setting was chosenthat related the ixiolite parameters directly to those of columbite-tantalite as given by Strunz (1957). This led to the spacegroup Pcan. The single- crystal and powder patterns are both consistent with the extinction rules required by this spacegroup. The unit-cell parametersderived from the precessionphotographs were refined by least-squarescalculations from the powder diffraction data. The resulting parameters are given in Table 3. Table 3 shows that the parameters of Sample M-11894 are slightly greater than those of sample M-6591. The reason for this difference has not been determined, since only the latter was analyzed chemically. IXIOLITE 967

T,tslr 4. Rrl.trroxsnrp Bnrwnrn rnn UNrr Crr.m or, Ixror,rrn, Colullnrrn-TaNTALTTEAND Woocnrrrn

Ixiolite, Columbite-Tantalite Wodginitel Skogbiile, Finland Tinton, S. D. Wodgina, Australia

AxiaI a:5 .73 a:5 .73 b:rr.47 (2x5.73) Lengths b-4.74 b:14.24 (3X4.75) a: 9.52 (2X4.76) (A) c:5 .16 c: 5.08 c: 5.10 900 900 0:91'18 Cell vol. r40 414 (3x138) ss7 (4X139) (49 Space group Pcan Pcan C2/c or Cc

1 From Nickel, et aI.,1963.

The unit-cell parameters of ixiolite are closely related to those of columbite-tantalite and of wodginite, the latter two being simple mul- tiples of the ixiolite cetl (Table 4). The close relationship between these minerals is also evident in their powder diffraction patterns. As shown by diffractometer tracings (Fig. 2), the ixiolite pattern can be distinguished from that of the other two minerals by the absenceof low-angle difiractions. The entire difiraction pattern of ixiolite is also more diffuse, the amplification having to be in- creasedby a factor of two to produce peak heights comparable to those of columbite-tantalite and wodginite. This accounts foi the higher back- ground in the ixiolite tracing. The measuredpowder difiraction data for ixiolite and an intermediate memberof the columbite-tantaliteseries are shownin Table 5. The inten- sities given in this table are integrated peak intensities measured from the tc-ray diffractometer tracings shown in Fig. 2, and,recalculated to maximum intensitiesof 100. The lines that were visible on the powder films, but not resolved on the difiractometer tracings were arbitrarily assignedintensities of 1. There is some uncertainty as to what indexing should be used for columbite-tantalite, since at least three axial settings are given in the literature. rt was decidedto adopt Strunz'setting of pcansirrceit follows the generallyaccepted convention of c1a1b. As stated previously,the ixiolite setting was chosenso that its parameters could be directly r.lut.d to thoseof columbite-tantalite.

Cnrurcal Couposrrror.r rt was decided to obtain a new chemical analysis for ixiorite becauseall previous analyseshad been done in the nineteenth century. and because 968 E. H, NICKE.L, J. F. ROWLAND AND R. C. IUICADAM

WOOGINITE

-a---.-----^;L'w llll tlll 65 60 55 50 a5 40 35 !o 23 20

Frc. 2. Diffractometer tracings of ixiolite, wodginite, and columbite-tantalite. copper radiation, nickel filter; scanning speed I degree per minute' of the uncertainty as to which of these were actually performed on ixio- lite. The ixiolite in sampleM-6591 was found to be suitablefor analysis becausethe sample was large enough to provide sufficient material, and there was no e'iidenceof any tapiolite being present in the sample. The samplewas preparedas follows: a portion of sampleM-6591 was broken off and gently crushed; the crushed material was then hand- picked under a stereomicroscope,only grains free of detectableimpuri- ties being selected.Approximately three grams of hand-picked ixiolite were obtained in this way. Although an r-ray diffraction pattern of this sample exhibited no extraneous lines, a small amount of contamination was neverthelessunavoidable, as shown by a polished section prepared from one of the ixiolite fragmentsl this revealed the presenceof micro- scopic veinlets of a mineral with low reflectivity. Although this mineral could not be isolated for identification, the chemical analysis indicated that it could be a hydrous calcium aluminosilicate. The results of the chemical analvsesare shown in Table 6, together with IXIOLITN 969

Telr,r 5. X-Rev Poworn DrnrnacrroN parrrnxs ol. Cor,uunrrn-TeNTAlrrn eNo fxror,rrr

Columbite-Tantalite, Ixiolite M-6591 Ixiolite Tinton, S. D. Skogbd,le,Finland (calc.)

lnt hkl Int.

12 /.I.t o20 4 5.30 110 48 3 .66 l.t(, 32 3.65 110 3.653 9 040 100 2.96 131 100 2.98 111 2.980 10 2.86 200 J 2.87 200 2.866 6 2.53 002 13 2.57 002 2.576 1n 2.49 20r 20 2.51 20r 2.504 12 2.38 060 2.37 o20 2.37r I 2.279 151 3 2.236 o32 z 2.265 012 2.263 i 2.207 231 4 2.213 211 2.214 2.084 132 9 2.104 tt2 2.105 3 2.O43 241 1 2.017 t2r 2.016 1 898 202 4 1.915 202 1.916 9 1.831 2fi 6 1.826 220 1.826 4 1.796 152,t7l t4 1.772 330 IJ 1.772 310 r.772 12 1.735 062 r7 |.746 022 r. t++ 22 1.721 261 24 1.722 22r r.722 a 1.672 331 I 1.608 8 1.534 133 t2 1.554 113 1.554 I 1.516 r90 1 t.521 130 r.524 + 1.484 262 I 1.490 222 1.490 l4 1.465 2os 1 1.473 I lzos t 29 1131 1.461 12 r.454 191,332) ls12 1.4ffi 1 r.432 400 1 1.393 1.380 401 I 1.380

The d-values were measured from 114.6 mm Debye-scherrer patterns. rntensities were measured from diffractometer tracings obtained with CuKa radiation. The calculated ixiolite spacings are from a unit cell with a:5.731, b:4.742 and c:5.152 A. the analytical data on other so-called ixiolite samples from Skogbiile, taken from the literature. Table 6 shows a considerablevariation in analytical results. This may be attributable in part to shortcomingsin early analytical techniques 970 E. H. NICKEL, J. F. ROWLAND AND R. C. MCADAM

Tesr-n 6. Cnnurcar, Ans,vsns on Ixrollrn lnou Srocltir-r, Frnr,.LNn

R. C. Norden- Rammelsberg(1871) McAdamt skiitld (1962) (18s7)

TarOo 61.47E"),'l l5.lI-/o 76.8rTo 85.857a 8+.4470 NbrOr 10.s0J

TiOz 0.38 FeO 8.08 980 9.49 t2.94

MnO 5.40 4.32 1.60 SnOr 12.27 9.67 9.r4 0.80 1.26 CaO 0.11 0.41 056 015 AlrOa 0.16 ZtAz 060 WOr 0.30 CUO 014 SiOr o.12 IIO- 0.08 HzO+ 0. 16

r This paper; sample no. M-6591.

andf or to lack of sample authenticity. It is quite possible,indeed likely, that some of the analysesmay be of tapiolite or of tapiolite-ixiolitemix- tures, as theseminerals are indistinguishableby eye. Semi-quantitative spectrographic analyses of ixiolite and tapiolite picked from the same sample (M-11894) indicate that ixiolite contains more tin than does tapiolite (Table 7) . Consequently, it seemslikely that only the analyses high in tin, i.e., thosein the first four columnsin Table 6, are of ixiolite' That some confusion exists regarding ixiolite and tapiolite is shown by the fact that the labelson the samplesobtained from the various collec- tions are not at all consistentwith the mineralsactually present' as was noted earlier. The atomic proportionsand unit-cell content calculatedfrom the new ixiolite analysis are shown in Table 8. In these calculations the CaO, AlrOa,SiO, and HzO have been disregarded,since these constituentsare probably due to impurities. The atomic proportions were multiplied by a factor to yield 12 atoms per unit cell. According to the data in Table 8, the formula for the ixiolite from sample M-6591 is Tar.zsFeo.zrSno.srNbo.roMno.aeZro.orTio.oaWo.orOz.e8'or' in generalizedform, XaOs.The specificgravity calculated from the unit- cell dimensionsand the unit-cell contentis 7.392. TXIOLI:I'D 97r

Taslr 7. Snur-QulNrrrarrvn specrnoonapnrc Analvsps ol rxror,rrn eNo Telrolrrn rnou S.qanpr.nM-l1894 lnoM Srocsdre, FrNlnNo (Figuresindicate order of magnitude in per cent)

Ixiolite Tapiolite

Ta PC PC no/ Nb L/A 2% Sn 5 2 Fe l+ 8 Mn ls 0.6 Zr 0.6 o.2 Ti 0.3 0.4 Mg 0.4 0.03 Ca tr o.4 Si o.2 0.4

PC: PrincipalConstituent Analyst:Miss E. M. Kranck

SrnucrunB The closecrystallographic relationship between ixiolite and corumbite- tantalite must be an expressionof a structural similarity between th e two minerals.rn the structure of columbite (sturdivant, 1930),the and niobium atoms lie within regular octahedra of oxygen atoms in crose- packed arrangement.The octahedrashare two edgesto form staggered

Tenr.r, 8. UNrr-Cnr,r,ConrrNr ol fxrolrrr,

Weight Atomic Atomsper Proportions Unit Cell

Ta 50.85 0.2810 |.752 Fe 6.34 0.1136 0.708 Sn 9.76 o.0822 0.5t2 Nb 7.42 0 .0798 o.497 Mn 4.23 o.0769 0.480 Zr u.45 0.0049 0.031 Ti o.23 0.0048 0.030 w 0.24 0.0013 0.008 o 20.48 1.2804 7.982

100.00 1.9249

r From the oxide percentages given in Table 6, recalculated to rN/6 after the ex- clusion of CaO, AlzOr, SiOz and HzO. 972 D,.II. NICKTJL,J. F. ROWLANDAND R' C' MCADA],I chains parallel to the c-axis,the chains being combined by shared corners. The metal atomsare in an orderedarrangement, any one chain consisting of Fe-O or Nb-O octahedra.The chains, themselves,are ordered, one chain of Fe-O octahedraalternating with two chainsof Nb-O octahedra along the 6-direction. In ixiolite, which has only four metal atoms per unit cell, and a space

lxiolite

Q rr,rerorC) orys"n

Columbite o lron C Niobrum o Oxygen

olz!rl 5el lllllll

Frc. 3. Structuresof columbi" ':1"::',""t;1";, structureis taken from $ff.r..t"-otte

group permitting only 4-fold and S-fold positions,this 2:l ordering is impossible. Consequently, the metal atoms in the ixiolite unit cell prob- ably occupy equivalent positions and can therefore be regarded as dis- ordered.If these atoms are placed in the (c) positions required by the spacegroup Pcan, then they lie fairly closeto the equivalent positions in the columbite structure occupied by niobium and iron. The relationship betweenthe columbite structure and the proposedixiolite structure can be clearlyseen in Fig.3, which is a projectionof the two structuresparal- IXIOLITE 973

Tasr,r 9. Coupmrsox Bnrwnru Car,cur,arrn eNn Olsrnvno Pownnn PetrnnN fwrrNsrrrns ol Ixrolrrn

Calculated Intensities hkl Measured Absolute Calc.to 100 Intensities

110 1414,500 23 32 111 633,500 100 100 200 29,ffi 5

002 118,500 19 IJ 201 174,4N 27 20 o20 78,000 t2 5 ol2 1l,400 2 ) 2tr 19,600 tt2 110,600 r7 9 12l 0 0 1 202 55,600 9 , 220 57,000 9 6 212 1,700 0.3 0

310 150,800 24 IJ 020 183,200 29 r7 221 259,10O 4l 1i 113 8 0 0 r22 0 0 0 113 160,200 25 12 130 25,400 A 1 222 41,300 6 1 203 103,200 roj 131 138,100 221 29 312 183,700 ?ol 400 17,200 J 0 32r 0 0 0 213 76 0 0 401 70,7ffi 11 1

lel to the ab plane. The chains are normal to the plane of projection. rntensity calculationshave beenmade to confirm this proposedixiolite structure. The oxygen atoms were placed in the eight (d) positions with x:0.250, y:0.092 and z:0.O79; theseparameters correspond to the averageoxygen positions in the columbite-tantalitestructure. The metal atoms were placedin the four (c) positionswith y:0.333, which corre- sponds to the averagey parameter of the Fe and Nb atoms in columbite. The intensities calculated from this structure are in good qualitative agreementwith the observedintensities (Table 9). From a quantitative standpoint, the measuredintensities are generally Iower than the calculatedvalues, which is to be expectedin view of the 974 E. H. NICKEL, J. F. ROWLANDAND R, C, MCADAM diffusenessof the diffraction pattern, as noted earlier. This diffusenessis probably due to structural irregularities resulting from ions of different size occupying equivalent positions in the structure. Taking this into ac- count, the agreement between calculated and observed intensities is sufficiently good to confirm the general structural scheme proposed for ixiolite. Like the structure of columbite, that of ixiolite can be describedas consistingof chainsof metal-oxygenoctahedra formed by the sharing of two edgesof eachoctahedron, with the chainsconnected by the sharing of one corner of eachoctahedron. This structure was first suggestedas a hypothetical possibility by Pauling and Sturdivant (1928) in their dis- cussionof the brookit.estructure. Actual examplesof compounds with this structure are o-PbOr (Zaslavskijand Tolkadev,1952),the orthorhombic form of ReO2 (Magn6li, 1957,) and disordered GaTaOs (Bayer, 1962). Nielsen(1956) appears to have beenthe first to suggestthe existenceof a disorderedtantalite, although he provided only scant evidenceto sup- port his contention. Donnay and Donnay (1961)pointed out that some specimensof columbite-tantalite (with Mn)Fe) have a distinctive morphology, indicating the probability of a unit cell one-third the size of columbite-tantalite, which correspondsto ixiolite.

RospoNspTo HEATTNG When ixiolite is heated in air, severalchanges occur in the x-ray diffrac- tion pattern. As shown by the difiraction data in Table 10, the d-values of the heated ixiolite are consistently lower than the correspondingd-values of the unheatedsample, indicating a reduction in interatomic distances. In addition, a number of new lines appear at high d-values, suggestingan increasein the degreeof atomic ordering. Several of the new lines corre- spond to olovotantalite (Iiterally "tin tantalite") from the U.S.S.R.' recently describedby Matias (1961). Matias' o-ray diffraction data are included in Table 10 for purposesof comparison. Unfortunately Matias was unable to obtain any single-crystal diffrac- tion data. His powder data, however,as well as that of the heatedixiolite, can be indexed on an orthorhombic unit cell with the approximate dimen- sions of the wodginite unit cell, i.e., a cell four times the size of ixiolite (Nickel et at., 1963).Confirmation of this unit cell, however, must await the results of single-crystal work on olovotantalite. The changesin the r-ray diffraction patterns were observedat tempera- tures of 700oCand over. The intensitiesof the extra lines were found to depend on the temperature, duration of heating time, and the cooling rate, as indicatedin Table 11. IXIOLITE 975

Tarrn 10. X-Rlv Poworn Dmlnacrrox p.lrrnnus or UNneerrt ANDHEATED Ixroutr, axl or Or,ovorANTALrrE

Ixiolite No. M-6591 Olovotantalite Line Unheated fleated to 9500 C (Matias,1961) No.

I (meas.) I (est.) I1 d (A)

I J 11.3 40 11.1 z 4 5.70 J t2 4.70 10 4.69 4 10 3.79 20 3.79 .) 32 3.65 50 3.62 6 100 2.98 100 2.95 70 2.95 ( 7 2.87 8 2.85 20 2.88 8 )n 2.76 9 13 2.57 a

1 Matias' intensity data were given on a scale of 10. His intensity values have been multiplied by a factor of 10 to bring them to a comparable scale of 100.

DrsonoBnnl CoruMerrB-Taurarrrr, oR psEUDo-fxrolrrE

During the course of the investigation, specimensfrom a number of different localities were found to produce r-ray powder difiraction pat- 976 E. H. NICKEL, J. F. ROII/LAND AND R. C. M2ADAM

Teerr 11. HurrNo ExpnnrrtrNts on Ixror.rrr M-6591

Temp. Time Cooling Intensity of Extra oc. hrs Rate Reflections

700 2 rapid nil 700 z slow weak 700 18 rapid weak a1 800 LA rapid moderate 800 18 rapid moderate 1L 800 L, slow strong 800 18 slow strong 950 t7 rapid moderate 950 1i rapid moderate terns that were very similar to ixiolite. After heating these samples under the same conditions as those used for ixiolite, low-anglelines ap- pearedin the diffraction patterns, but these extra lines, which occur at 7.1 and 5.3 A, are not characteristicof heated ixiolite but of columbite- tantalite. If it is assumedthat the absenceof the low-anglediffraction peaksis due to cation disorderand that their presenceis due to cation order' then it is apparent that, on heating, the cations in the two types of mineral must becomeordered in different ways. This is probably related to com- positional difierencesand, since one of the criteria in Nordenskirild's original definition of ixiolite was its composition, then the ixiolitelike minerals that convert to columbite-tantaliteon heating cannot be con- sideredas true ixiolites. For want of a better name, it is suggestedthat they be referred to as disorderedcolumbite-tantalite' or as "pseudo- ixiolite." One of these pseudo-ixiolites,labelled "Manganotantalite, Green- bushes,Australia" was obtained from the GeologicalSurvey of Canada. ft was analyzedchemically and the results are shown in Table 12' This analysis difiers from that of ixiolite chiefly by virtue of its high

Te.nrc 12. Cnnrtcar, Aller-vsrs or Psnrmo-Ixror-rrn (MeNc.tNorANTALrrE) rnoM GnnnNeusnns, Ausrn-llle

Ta:os 68.934k Nb:os t5.42 MnO 13.82 FeO 1.05 SnOz 0.48 ee.70% I XIOLIT D 977

MnO:FeO ratio and its low tin content. It is unlikely that the high manganesecontent alone is responsiblefor the difierent responseto heat- ing, since Nielsen (1956) reported crystals of FeTazOobeing converted from a disorderedform to normal tantalite. The determining factor is therefore probably the tin content. This conclusion derives support from the fact that the low anglelines of heated ixiolite correspondto lines in the olovotantalite pattern, both minerals containing substantial amounts - - of tin (ixiolit e 12.27/6 SnOz; olovotantalite 9.06/6 SnOz) . Severalother samplesproduced the same*-ray powder patterns before and after heating as the Greenbushesspecimen, and can consequently alsobe regardedas pseudo-ixiolites. One of them is a sampleof "tantalite" (B.M. 35301)from the Ilmen Mountains in the Urals, obtained from the British Museum. The r-ray powder data for this mineral were included in an early edition of the A.S.T.M. card index (card no. 2-0691),but the card has been deletedand doesnot appear in more recent editions. An- other sampleis from the Varutrdsk in Sweden,obtained from ProfessorQuensel. This specimen (no. 7039) is noted in a paper by Amark (194I). Still other specimens of pseudo-ixiolite were found in samplesfrom a pegmatitein SteeleTownship, Ontario. There are severalliterature referencesto minerals with powder difirac- tion patterns similar to that of ixiolite. Schrcjcke(1961) reported powder data for a synthetic FeNbzOo,which correspond to the ixiolite powder data. Hutton (1959) presented data for what he termed a partially metamict columbite (manganomossite) from Yinnietharra, W. Aus- tralia, that produced a-generally weak difiraction pattern with no low- angle diffractions. After heating, the mineral was reported to produce the normal columbite-tantalite pattern. There is probably a gradation from a completely ordered end-member (columbite-tantalite) to a fully disordered one (pseudo-ixiolite), the degreeof orderingbeing indicated by the intensitiesof the 7.1 and 5.3 A difiractions. The powder pattern of pseudo-ixiolite from Greenbushes, Australia, for example, did not contain these lines, although single- crystal films had some very weak spots indicating the larger unit cell (columbite-tantalite); consequently, it is not completely disordered. Berman'sdata (1955)for columbitefrom Mitchell County, N. C. indicate a powder pattern with a weak 7.1 Aline that was enhancedby heating; this sample presumably has an intermediate degreeof ordering. At present there is insufficient data to correlate degreeof ordering with composition.C. O. Hutton (1959) attributed disorderingin his mineral from Yinnietharra, W. Australia to the presenceof radioactive elements. Donnay and Donnay (1961) found that members with a high Mn:Fe ratio have a characteristic morphology that they attribute to a disordered 978 N. II. NICKDL, J. F. ROWLAND AND R, C. MCADAM structure. On the other hand, the data presentedby Nielsen (1956) and Schr

AcTNowlBoGMENTS The authors are grateful to the following individuals and organizations for providing mineral samplesfor this investigation:Dr. J. A. Mandarino of the Royal Ontario Museum, Mr. J. L. Jambor of the GeologicalSurvey of Canada, Dr. E. J. Olsen of the Chicago Natural History Museum, ProfessorPercy Quenselof the University of Stockholm,Dr. M. H. Hey of the British Museum (Natural History) and Dr. J. H. Lord of the Geo- Iogical Survey of Western Australia. The authors are also indebted to Dr. Michael Fleischer of the U. S. Geological Survey, Washington, D. C. and to Professor Fritz Laves of the EidgencissischeTechnische Hochschule in Ziirich for providing certain referencesand for making some helpful suggestions.The investigation was materially assisted by the technicalstaff at the Mines Branch,including Mr. D. J. Charettewho made severalof the chemical determinations,Miss E. M. Kranck who provided the spectrographicanalyses, and Mr. D. Owens who prepared the diagramsand photomicrographs.

RnlpnrNcns Alrmr, K. (1941) Minerals of the Varutriisk Pegmatite. XXIX. An X-ray Study of Stanniferous Columbite from Varutriisk and of the Related Finnish Minerals Ainalite and Ixiolite. Geol.Fiiren. Fbrh.63,295-299. B,lvrn, G. (1962) Isomorphie- und Morphotropiebeziehungen bei Oxyden mit TiOrTyp und verwandten Strukturen. Doctoral Thesis, Eidgendssische Technische Hochschule, Ztirich. Bnnuar, J. (1955) Identification of metamict minerals by x-ray difiraction. Am. Mi.neral 40, 805-827. DoNNev, J. D. H. ern G. DoNrav (1961) Ebauche d'une structure cristalline par analyse morphologique. CornptesRend,us, 252, 1982-1983. Hnv, M. H. (1962) An Intletc oJ Minera.l Species and Vorieties. British Museum (Natural History), 2nd ed. Hurtox, C. O. (1959) Manganomossite restudied. Am. Mi,neral.44,9-18. Mrcnfrr, L (1957) Studies on rhenium oxid,es.Acta Chemico Scand. 11,28-33. Mettas, V. V. (1961) Olovotantalite, a New Variety of Tantalite. Geol. Mestorozhd,.Red.. E|,em.9,30-41 (in translation by Michael Fleischer). Nrcrnl, E. H., J. F. Rowr-eNo axo R. C. McA-oeu (1963) Wodginite-a new tin man- IXIOLITE 979

ganese tantalate from Wodgina, Australia and Bernic Lake, Manitoba. Canad.ian Mi,neral 7,390-402. Nrnrsrx, H. (1956) Strukturuntersuchungen am Tantalite. Phot. u. Wiss. S,3-8. NomeNsrrcir-o, A. E- (1857) Beitrag zu Finnlands Mineralogie. Ann. phys. u. Chem. 4th ser.. ll. 625-634. Par.ecnr, C., H. BnmrnN eno C. Fnoxnu- (l9M) The System oJ Mineralogy, 7th ed., John Wiley and Sons,Inc., New York, vol. I, p. 778. Paulrxc, L. eNn J. H. Srunorvaxr (1923) The of brookite. Zeit. Krist. 68,239-256. QunNsnL, P. (1941) Minerals of the Varutriisk Pegmatite. XXX. Cassiterite and stannif- erous columbit e. Ge ol. F br en. F ()"/h. 63, 300-3 10. Rrunoun, P. (1960) Die Drzmineralien und ihre Verzuachsungen3rd ed., Akademie Verlag, Berlin. Rartltttslenc, c. (1871) Uber die Zusammensetzungder nati.irlichen Tantal- und Niob- verbindungen, zundchst des Tantalits, Columbits und Pyrochlors. Monatsber. Akad. Wiss. Berlin, 157-205. Rosr, H. (1853) Uber die Zusammensetzungder in der Natur vorkommenden Tantalsdure haitigen Mineralien. Ann. Phys. u. Chem.4th ser.,14, 85-101. Scnncicxo, H. (1962) Heterotype Mischbarkeit zwischen Wolframit- und Columbitgruppe. Beitr. Min. Petr.8,92 ll0. Srunsou, E S. (1909) Further occurrences of tantalum and niobium in Western Australia. Austy. Ass.Ada. Sei.12, 310-315. SrnuNz, H. (1957) MineralogischeTabellen.3rd ed , Akad. Verlag, Leipzig, p. 383. SrunorvaNr, J. H (1930) The crystai structure of columbite, Zeit. Krist., Abt. A,75, 88-108. Vrnx,r.osrV, V. I. ar.ro A. E. Frnsuen (1910) Ob Ixionolit iz Il,menskikh Gor. Izo. Imp. Akad..Nauk, 6th ser.,4, 511-516. Zasr.avsrt;, A. L enn S. S. Torxe6nv (1952) The structure of modification of lead oxide. Structure Reports 16, 224-225.

Manuseript receiaed,,Morch 8, 1963; acceptedfor publication Aprit 29, 1963.