American Mineralogist, Volume 63, pages 28-36, 1978

The crystal structureof loveringite-a newmember of the crichtonitegroup

BnveN M. Glrruouss Chemistry Department, M onash Uniuersity Clayton, Victoria 3168,Australia

IeN E. GnEv CSIRO, Diuisionof MineralChemistry,P.O. Box 124 Port Melbourne, Victoria 3207, Australia

InN H. CeNrpssLL'ANDPATRIcK KEU-v Earth SciencesDepartment, Uniuersity of Melbourne Parkuille, Victoria 3052, Australia

Abstract

Loveringite,a new calcium iron titanate,was discoveredin the JimberlanaIntrusion near Norseman, Western Australia. The unit-cell composition of the type sample,normalized to 38 oxygens, is Caoz2REE' $(Y,Th,U,Pb)o ouTi, orFe. ,"Cr, ,oMgo bsAlosrv, ,,Mno orOrr, ""Zro which may be abbreviatedas AMro"nOr",A: 2large cationsand M: ) small cations (including some REE). The mineral containsabout 0.2 percenturanium and is metamictin its natural state.The of the type grain was reconstitutedby heating in air at 800"C. Single-crystalX-ray diffractionstudies showed it to haverhombohedral symmetry, RJ, with unit-cellparameters a,n : 9.1l7(4)A, a,n : 69.07(I )o. The structurewas solvedusing 398 observed [l > 2o(l)l symmetry-independentreflections, refined to an R value of 0.043. Loveringiteis isostructuralwith senaiteand crichtonite,with a structurebased on a nine-layer (hhc. . ) close-packedanion lattice in which the I cation occupiesan anion site and the M cations are ordered into 19 octahedraland 2 tetrahedralsites per unit cell. Microprobe analysesfor a number of loveringitesamples are reported, and the observed compositionalvariations are discussedin relation to the structure.

Introduction cations occupy both octahedraland tetrahedralinter- We have recentlyreported the crystal structuresof sticesin the close-packedlattice. the minerals senaite (Grey and Lloyd, 1976) and As part of a generalstudy on minor phasesoccur- crichtonite (Grey et al., 1976). These minerals are ring in the Jimberlana Intrusion near Norseman in isostructuraland have compositionsdescribed by the Western Australia, we identified a mineral with a generalformula AM2tOa8,where M : small cations, composition very similar to that of crichtonite and predominantly Ti and Fe, and A : large cations senaite,but with calcium as the major large cation. (mainly Pb in senaite and Sr in crichtonite). The An X-ray diffraction study showed that the mineral compounds have rhombohedral symmetry, and the was metamict, due to radiation damage from the structuresare based on a close-packedanion lattice uranium present (approximately 0.2 weight percent with a stackingsequence (hhc. ..) and with the large UOz). Crystals reconstituted by careful heat treat- cations occupying one of the anion sites.The small ment exhibited rhombohedral symmetry with unit- cell dimensionsvery similar to those for senaiteand crichtonite. Its isostructural relationship to these I Present address: The Department of GeologicAl Sciences, minerals was confirmed by a single-crystalX-ray Queen'sUniversity, Kingston, Canada structure analysis,which is the subjectof this paper.

0003-004x/78l0r02-0028$0200 2g GATEHOUSE ET,4L.: LOVERINGITE 29

Analytical data for a range of samples are also re- werealso observed,although these elements showed ported. no obvious replacementcorrelations with other ele- ments. Occurrenceand compositionaluariation The iron-chromium substitution correlateswith The mineral loveringite2was found during a study the positionof the mineralin the layeringsequence. of uranium-bearingphases of the Jimberlana Intru- Loveringitesamples taken from the -hy- sion near Norseman, Western Australia (Campbell persthenelayer had negligiblechromium contents ( S and Kelly, in press).The phaseswere located by the 0.1 weightpercent). At the contactof this layerwith lexan print method (Kleeman and Lovering, 1967), the underlyingbronzite cumulate layer, the chro- and identified using a scanningelectron microscope mium contentof the loveringitesshowed a sudden equipped with a multichannel analyser. jump to 3 or 4 weight percent,whereas the iron Jimberlana is a layeredintrusion which containsa contentsshowed a concomitantdecrease. All samples repeatedsequence of and bronzite cumulate taken from the bronzite layer had appreciablesub- layers overlain by a thick plagioclase-augite-hyper- stitution of chromium for iron, up to a maximum sthene cumulate layer (Campbell et al., 1970). Love- replacementofabout 50percent ofthe iron present. ringite is most abundant in bronzite cumulatelayers, Calcium-rareearth substitutionshowed a similar but even in theserocks it rarely exceeds5 grains per trend to iron-chromium,with the samplestaken slide. The mineral is also found in the lower half of from the plagioclase-hypersthenelayer generally dis- the plagioclase-augite-hypersthenecumulate layer, playingthe highestcalcium-lowest rare earth analy- but has not yet been recorded in the olivine cumu- ses.Sample Cl87-31 in Table I is an exceptional lates.It occurs as isolatedcrystals which are usually exampleof this. It is an almostpure calciumend- anhedral but occasionallyform needles.The grain memberphase, with 94 atompercent contribution of size rarely exceeds 100 X 50 pm. The mineral is calciumto the large-cationsgroup. This samplewas closely associatedwith either quartz and K-feldspar alsounique in havingthe highestvanadium and low- intergrowthsor phlogopite.Other uranium and rare- estzirconium contents of all the specimensanalysed. earth bearingaccessory minerals in the cumulatelay- Unfortunately,this sample was too small(0.03 mm X ers are baddeleyite,apatite, zircon, sphene,and ru- 0.01 mm) for X-ray study,and was also damaged tile. Ilmenite and are also common. duringexcavation from thesurrounding silica matrix. The compositions of more than thirty grains of The compositionalvariations are discussed in rela- loveringitewere determinedby microprobe analyses. tion to the structureof loveringitein a latersection. The detailed interpretation of these results will be published elsewhere(Campbell and Kelly, in press). Experimental To illustrate the wide ranges of metal-atom sub- Naturalloveringite has an interestingtype of meta- stitutions observed,the resultsof microprobe analy- mict structure,in which thereis a breakdownin the seson five grains are given in Table l. SampleCl l6-5, metalatom orderingbut the close-packedanion lat- Table 1, was used for the single-crystal X-ray diffrac- tice remainscoherent enough to give a sharpdiffrac- tion study, after restorationofthe crystalstructure by tion pattern.Individual grains of the mineralgave heatingin air at 800"C. The analysison this grain was single-crystalX-ray diffractionpatterns consisting of performed after reconstitution,and so the elements sharp spotswhich all indexedon a hexagonalcell, a are consideredto be in the valencestates pertaining : 2.87,c : 20.67A. This correspondsto the strong to the oxidizing conditions used, r'.e.Feg+,Y5+ etc. pseudo-cellobserved for crichtonite(Hey et al., These are shown as oxides in Table L The analyses 1969),and is due to diffractionfrom a close-packed illustrate two main types of isomorphous replace- anion arraywith a (hhc...) stackingsequence; i.e. ment, i.e. iron-chromium and calcium-rare earth. ch"* 9 X anion layer repeat.The atom dis- Significant variations in the amounts of titanium placementsinduced by radiationare apparentlyonly (54.6-64.1weight percent),vanadium (0.5-4.5weight slight,and a singleheating for onehour at 800oCwas percent), and zirconium (1.2-6.1 weight perceni) sufficientto reconstitutethe mineral. The resulting single-crystalX-ray patternswere similar to thosefor senaiteand crichtonite. The rhombohedral symmetry 'The and the proposal for system- name for this new mineral the was confirmed from precessionand Weissenberg atic nomenclature of the crichtonite mineral series has been ap- proved by the IMA Commissionon New Minerals and New Min- photographs. eral Names. For the structuredetermination, a reconstituted 30 GATEHOUSEET AL,,,LOVERINGITE

Table l. Microprobe analyseson loveringitesamples from Norseman, Western Australia, and davidite from Olary, South Australia

c115-5 c 193-2 N138-17 c187- 3I RRD4-291-5 Davidite fron (Data crystal) o1ary, South Australia

rio 58. 34 59. 15 64. LO 55.35 5r.'t 4 2 54,67 olzo: o.94 o. 58 1. 54 o.22

'-2- 20. 25. 30 3 15.77 24. L5 26.16 20.a4 58 MnO 0. r7 o. 13 0.03 o.2L o. l3 0.04

Mqo 2. 18 r.22 0.63 o.6'l 0. r0

Cao 2.37 2.50 3.43 4.54 r. 45 o.23

ct203 9.94 0. t0 0. 06 0, 15 6. 90 I.2I

s j.o2 0. o7 0.57* t le

Na2O 0. 06 o. 13

K2o o. 04

Nio 0.08 0. o7 0. 11 0.03

uo2 o. 18 0. 17 o. 34 0. 18 6.42

Pbo o.22 o.23 0. 1s 0.05 0.69

Hfo2 0. 35 o.20 0.03 0. 11 0. 16 o.51

ZrO2 4. l8 6.r2 I.2T 4. 24 0. 07

Tho2 0 .09 o.52 o. 53 0,09 0, 34 o. 05

CeO2 r.2a I.12 t. 21 o.26 2.75 3. O6

I.22 0. 84 0. 78 0. 08 2.43 ""2o3 *d2o: o,24 o. 15 o.42 o. 05 o. 35

uzo5 l. 10 o.94 0.37 4.40 1.4r 2.AA

Y^O^ 0. 09 0. 10 0. r4 o -2'7 t. 86

R.E.E. o.26 0. 21 0, 19 0. 03 0.30 0. 88

SrO 0.0I o.02

Total 99.2L 98.28 97.L2 100. 10 99.2I 98.98

Samples N138-17 ild C187-31 measured 0.005 m x O.05 m ild O.Ot m x O.03 m respectively, si md Na @ntribution fron surrouding natrix for these very small crystals. **other rare earth contrilutions estinated frm chondrite nornalized rare earth patterns.

crystal measuring0.03 X 0.05 X 0.07 mm was trans- 12.18'.A 0-20scan, 3-250, was usedwith a variable ferred to a Phillips PWll00 4-circle automatic dif- scan width given by L0 = (1.2 + 0.3 tan d) and a fractometer. Least-squaresrefinement of 20 values speed of 0.05o sec 1. Two background measure- obtained for centred high-anglereflections gave the ments, each for half the scan time, were made for rhombohedralcell parametersdrh : 9.ll7 (4)A, drh : eachscan, one at the lower and one at the upper limit. 69.07(1)'. The correspondinghexagonal parameters The intensitieswere processedusing a program writ- ?re 46sa: 10.337,ch.* : 20.677A, i.e. Jl3 and I ten for the PWI100 diffractometerby Hornstra and times the subcellvalues respectively. Stubbe (1972). Becauseof the very small size of the Intensities were collected with graphite mono- crystal (p.R : 0.20) an absorption correction was chromated MoKa radiation with a tower angle of not applied. However, a partial compensationwas CATEHOUSEET AL.: LOVERINGITE 3l achieved by averaging the intensitiesof equivalent M(l) gavea marked improvement in the B value for -0.1, reflectionsin the rhombohedral cell. Thus the reflec- this site, although it still remainednegative at tions measuredwere reduced to a unique set of 844 and the R factor dropped to 0.06. A differenceFou- reflections.Due to the very small crystal volume, a rier calculated at this stage showed a positive peak large number of reflections were extremely weak. correspondingto about 3 electronsat siteM(l)' This Lessthan half (398) of the unique reflectionshad 1 ) was interpretedin the light of the calculatedchemical : 2o lll and were used in the structure refinement. formula, ArrMrornOrr, where A Ca + REE + Scattering-factorcurves for Ca, La, Ce, Ti, Fe, Cr, (Y,Th,U,Pb), as indicating some ordering of the ,4 Mg, Zr, Al, V, and O were taken from Inlernational cations into M(l), which is the largestoctahedral site Tables for X-ray Crystallography III (1962, p. 201ff). in both senaite and crichtonite (Grey et al., 1976). The curves for Ce, La, and Zr were corrected for Accordingly, 0.1 REE were ordered with the Zr and anomalousdispersion. All computing was performed Mg into siteM(l). on rhe Monash University cDC 3200and the cslRo A new set of composite scatteringcurves for the CDC 7600 computers. metal atom sites was prepared, consistentwith the At the completion of the intensity data collection, unit-cell composition. The deficiencyin the number the crystal was prepared in a polished mount and of small cations, 2M : 20.34 relative to the number analyzed on a JEOL electron microprobe, using a of sites, 21, was met by incorporating vacanciesin samplecurrent between0.2 and0.4 pA with the beam sitesM(2) andM(3). The reasonfor this is outlined in focused to about 5 rrm. Most of the elementswere the discussion.Least-squares refinement of all posi- measured at 15 kV, but Pb, Hf, Zr, Th, Nd, Ce, tional and isotropic thermal parametersgave a final La, Y, and Sr were determinedat 20 kV. The results R factor of 0.043 for all observed data. The site of the probe analysis are given in the first occupanciesare given in Table 2, together with the column of Table I (Cl16-5). The calculatedunit- refined coordinates and isotropic temperature fac- cell composition normalized to 38 oxygens tors. The observed and calculated structure factors is ICao.rrREEo3s(Y,Th,U,Pb)oou][TirrnrFer.rrCrr.rnare given in Table 3. Although the site occupanciesin Mgo sBAlo.sevo,rMno on]Orr.This may be general- Table 2 give compatible size groupings of cations, "rZro ized as ArrcM2o.24orr,where A: large cations,M : and lead to satisfactorythermal parametersfor all small cations. sites,it should be emphasizedthat they were derived mainly by crystallochemicalarguments. Many details Solution and refinementsof the structure are open to debate,e.g. the relativedistribution of Fe The atom coordinatesobtained for senaitein the and Mg betweensites M(l) and M(2), and the alloca- centrosymmetricspace group R3 (Grey and Lloyd, tion of the fractional occupancy of octahedral and 1976)were usedas a startingmodel for loveringite.In tetrahedral sites,i.e. the way in which the 20.34 M determiningthe distribution of the cationsamong the cations are distributed among the 2l crystallographic differentsites available, we were guided by the results sites.This will correlatestrongly with the orderingof for senaite and crichtonite, which showed ordering similar-sized ions, such as Mg2+ and Zro+, with sequencesbased on the size of the cations.Accord- widely differentscattering powers. However, because ingly, composite scatteringcurves were preparedfor of the large number of different elementsinvolved in the sites in loveringite consisting of Ca * REE in the ordering process,independent least-squaresre- M(0), Mg in M(l), Mg * Fe in M(2) (wherethe iron finement of both temperaturefactors and site occu- is presumably partly Fe2* in the mineral before re- panciesis not possible,and we are left with crystal- constitution), Cr, V, Fe in M(3), and Ti, Alin M(4), lochemicalreasoning as the only recourse. M(5).Tetravalent Zr was included with Tia+ in sites Description of the structure M(4) and M(5). A number of cycles of full-matrix least-squares Loveringite is isostructural with senaite and refinement led to satisfactory convergenceof all posi- crichtonite.The structureis basedon a close-packed tional parametersat a conventionalR value of 0.08. anion framework with a nine-layerstacking sequence However, the isotropic temperature factors showed (hhc... ) and with the large cations,mainly Ca and some seriousdiscrepancies. In particular, M(l) had REE, occupying anion sites. The small cations oc- an associatedlarge negativeB value of - 1.4,whereas cupy octahedral and tetrahedral interstices between the valuesfor the other metalsranged from 0.3 to 1.5. the close-packedanion layers.There are two typesof Transferring all the tetravalent zirconium to site cation layers, illustrated in Figures I and 2' Metal GATEHOUSEET AL.,' LOVERINGITE

Table2. Loveringite:final atomiccoordinates and isotropictemperature factors

s2 Atom Sj-te Occupecy x Y B(A)

M(0) O.'12Ca + O.23 R.E.E. + 0.05 (Y, Th, U, pb) o. ooo0 0. 0000 0.0000 2.11(11) M(r) O.58 zx + O.1 R.E.E. + 0.32 Mg o.5000 0. 5000 0. so00 o.77 (71 M(2) 0.60 Mg + 1.23 Fe 0.3r09o(15) 0.31090(ls) 0.31090(ls) 0.69(8) M(3) 2.24 Cr + 2.19 Fe + 0.86 Ti + 0.21 V o.34754(34\ 0.12318(33) 0.021s6(34) o.72(51 M(4) 5.81 Ti + 0.I9 A1 0.3084r(36) 0. 72081( 33) 0.r4s88(37) O.63(s) M(s) 5.81 Ti + O.I9 Al o.476L2 (38) 0.08155(3s) 0.639'77(37) 0.75 (s)

o(r) 6.00 0 0. 30s8(13) 0.6269(13) 0.3801(13) O.92(19) o(2) 6.00 0 0.1523(14) o.237A(14', 0.9393(13) 1.14(21) o(3) 6.00 0 0.921r ( 12 ) o.45'1r(r2',, 0.3oo2(r3) 0.47(15) o(4) 6.00 0 o . 1427(rAJ 0.5149(14) 0.9908(14) 1.16(17) o(s) 6,00 0 o. 3901( t4) 0.4896 ( 14) 0.134s(14) 1.11(18) o(6) 6.00 0 0. 7104( 12) o.24IO (L2) 0.0699(r3) 0.ss(16) o(7) 2.00 0 0.2r20(8) 0.2120(8) 0.2r20(8) o.55(33)

*Note y, reversal of order of z c.f. that in senaite (crey and Lloyd, 1976) rcsultinq fron opposite dixection of unique axis in data collection.

atoms M(l) and M(3) occupyoctahedral sites be- possiblein theseminerals as illustratedin Table 1, tweenpairs of hexagonal-stackedanion layers,r.e. and alsoTable I in Grey et al. (1976),the one con- h-M-h, Figure l, whereasM(2), tetrahedral,and stant crystal-chemicalfeature is the high degreeof M(4), M(5), octahedral,form h-M-c layersbetween orderingof tetravalenttitanium cations into the oc- adjacenthexagonal and cubicanion layers, Figure 2. tahedral sitesM(4) and M(5) within the h-M-c lay- Furtherstructural details are givenin the paperson ers. This is reflectedin their averageM(4)-O and crichtonite(Grey et al., 1976)and senaite(Grey and M(5)-O separations,which are L976(18) and Lloyd,1976). 1.964(18),1.969(7) and 1.967(7),and 1.970(ll)and 1.970(ll)A respectivelyfor senaite,crichtonite, and Interatomic distances loveringite.These are identicalwithin experimental Polyhedralbond lengthsand angles for loveringite error and agreewith the averageTi-O distanceof are given in Table 4. The averageinteratomic dis- 1.96(2)in brookite(Baur, 196l) which alsohas a tancesare very similarto thosefor both crichtonite mixed(chch. ' ' ) stackingof close-packedoxygen lay- and senaite.The greatestchange is associatedwith ers and with each TiO. octahedronsharing three site M(l). This siteis occupiedmainly by the large edges.In loveringite,the M(4) andM(5) atomsalter- divalent manganesecation in senaite,M(l)-O : natein six-memberedrings of edge-sharedoctahedra 2.227A,and crichtonite,M(1)-O : 2.205A,whereas within a h-M-c layer as shown in Figure 2, and in loveringitethe major contributoris the smaller betweenpairs of h-M-c layersthe octahedraalso tetravalentZr cation,M(l)-O : 2.166A. share edgesto form clustersof four octahedraas Within the associatedexperimental errors, there is shownin Figure3(i). Also shownin Figure3(i) is the no effectivechange in the M(O)-O distancefrom linking of the M(2)O1tetrahedra to the four-octa- senaite,2.817(17)A, to crichtonite,2.792(7)A, to hedraclusters. This particulararticulation of poly- loveringite,2.789(l I )A, eventhough the radius of the hedrais actuallythe basicstructure unit for B-GarO, dominant large cation changesconsiderably from (Geller,1960) and is foundin GanTi,On.,which is a L49A for lead,to 1.40Afor strontium,to 1.35Afor rutile-betagallia intergrowth (Lloyd et al., 1976).ln calcium(Shannon and Prewitt,1969). It would thus the lattercompounds, the edge-sharingof octahedra seemthat the M(0)-O distancein thesecompounds is extendsinfinitely in onedirection to build up double determinedmainly by the close-packingof the oxy- chainsas shownin Figure3(ii). It is interestingthat gens.The averageoxygen radius is approximatedby virtually identicalvalues are obtained for the M-M 0.5a6.*yffi, which gives 1.440,1.439, and 1.436A separationsacross shared edges in loveringiteand respectivelyfor senaite,crichtonite, and loveringite, GaoTirrO.r.In both cases,the inter-chainshared-edge i.e. for the latter two cases,the oxygensare somewhat repulsionsare considerablygreater (loveringite and largerthan the ,4 cations. GaoTi,Oor,both 3.224) than the intra-chainM-M Despitethe wideranges of elementalsubstitutions values(loveringite 2.99, GanTi2l0.o 2.97 A). GATEHOIJSEET AL.: LOVERINCITE JJ

Table3. Observedand calculatedstructure factors for loveringite

,o 6q GATEHOUSEET AL,: LOVERINGITE

ally havemore than one I cationper unit cell (e.g. see analyticaldata of Pabst,l96l). The chondrite-nor- malizedREE distributionpatterns for daviditesshow the samedouble-maxima as for loveringites(Camp- bell and Kelly, in press). Another compositionalcomplication in the love- ringitestructure was that the total numberof small cations,>M : 20.34(including 0.1 REE) wasless than the numberof occupiedsites, 21. This most likely occursbecause all iron was consideredto be Fe3+,all vanadiumY5+, etc., in the reconstituted mineral.By analogywith reportedchemical analyses on isostructuralminerals, it is certainthat, in the originalcrystal, these elements were at leastpartly present Fig. l. Polyhedralrepresentation of the metalatom M(l), M(3) in theirlower valence states. In the datacrys- arrangementbetween pairs of hexagonalStacked anion layers, tal, for example,if one-thirdof the iron wereferrous, viewedapproximately down [001]h*. the calculatedunit-cell composition would then have 2M : 2l and therewould be no vacanciesin the small cation sites(assuming no other sitesbecome Composition-structure relationships occupied).Consistent with this interpretation,the In the refinement of loveringite, electron-density vacancieswere considered to beassociated with those and bond-length calculationsindicated that a small sitesto whichiron wasassigned, i.e. M(2) andM(3). amount of an atom both heavier and larger than Zr A further structuralvariation in the loveringite and Mg occurred togetherwith theseelements in the samplesis suggestedby analysesfor grainssuch as octahedralsite M( I ). Also, when the unit-cellcompo- N 138-l7 andC 187-31,Table l. For thelatter sample, sition was expressedin terms of largecations A : Ca, the calculatedunit-cell composition, normalized to REE, Pb, U, Th, Y, and small cations M : Ti, Fe, 38 oxygens,is [Ca,gnREEo.ob(Y,Th,U,Pb)o.oo] Cr, V, Zr, Mg, Al, Mn, a formula of Ar-roMro.roOr" [Tirr.rrFe. 32VosoAlo 5sMgo.r.,Zr o.r.(M n,Cr)0.0, ]Oss, i.e. was obtained.Accordingly, the excessI cationsover Ar4sME.42Osr,where ,4 is predominantly Ca. This those required to fill site M(0) were ordered into site large atom is unlikely to substituteinto the octahe- M(l). Justification for this is found in a detailed dral site M(l), and it is necessaryto find an alterna- electron-probe analysis for REE in loveringite tive site for the 0.43 A atoms above that required to (Campbell and Kelly, in press).The REE distribution fill site M(O). A likely possibility is that the extra A pattern showed a maximum at La with a continuous occupiesthe remaining anion site on the trigonal axis decline to Eu, then a secondbuild-up maximized at [two-fold site O(7) in Table 2]. The formula may then Ho, declining again to Lu. This unusual double- hump REE pattern suggeststhat REE are entering two distinct sitesin the structure.The ionic radius of the La8+, 1.32A, is very similar to that for Ca2+, I .35A, in l2-fold coordination (Shannonand Prewitt, 1969), and there is no doubt that the larger REE occupy site M(0) in the anion framework, along with Ca. On the other hand, the ionic radius for Ho3+, 0.8944, is virtually identical to that for Y3+,0.892A, in six-fold coordination. Yttrium is known to closely correlate with Zr in many mineral structures,and so the secondREE enrichment,centered at Ho, is due to thesesmaller REE entering the M(l) octahedralsite, along with Zr and Y. It is highly likely that tetrava- lent Hf also occupiessite M(l), and the possibilityof sometetravalent Ce, ionic radius : 0.80A, in this site Fig. 2. Polyhedralrepresentation of the metalatom M(21, M(4), cannot be discounted.The occupation of the M(l) M(5\ arrangementbetween hexagonal- and cubic-stackedanion site by small REE also explainswhy daviditesgener- layers,viewed down [001]5...The filled circlesrepresent calcium. GATEHOUSEET AL..' LOVERINGITE 35

(1961)for the be generalizedas lr-,f, M"Otu where f : vacancy' axis, a situationsuggested by Pabst analy- i.e. it is assumedthat both I cations and oxygen isotypicmineral davidite. Pabst used chemical for iron) anions cannot both occupy the same anion site' In ses(including valence-state determinations unit-cellcom- this situation there are no oxygenson the three-fold and specificgravity data to determine

Table 4. Loveringite-interatomic distances(A) and angles (')

o'u-o sqle Dlstee G!|-O mEle DlBtance O-lt-O angle Dlsbilce

il(0) Stte n(I) octrhedrcn !l(2) tetrahedron

- H(O) - O(2) t6l 2.772 r(t) - o(I) t6l 2.186' H(2) O(5I t3l L.971 - 2.ao7 _ o(7) 2.O47 0(6) t6l - 112.32 o(2) - O(6) t6l 2.73 59.0r o(rt - otrll t6l 3.ol gB.16* o(s) otslr t3l 3.2s lr r06.44 o(2) - o(2) t6l 2,76 59.6r - o(t) t6l 3.ll 9r.84 - O(7) t3l 3.22 o(6) - o(6) t6l 2.a2 orz) - o(6)l t5I 2.a6 61.66

il(s) octahedron r(3) octahedron u(4) octahedlon

- u(5) - o(I) 1.895 rr(3) - O(4) r.935 l,|(4) O(2) 1.878 - o(4) I.877 - o(3) t.972 - o(rl L.992 - o(3) 1.908 - o(2) - o(3) r.960 I - o(s) I.984 - o(l) 1.9s7 - o(5) 1 .934 - 2.038 _ o(5) 2.000 o(6) - o(7) r,990 r r I - o(s) 2.L20 - o(z) 2.039 _ o(o) 2.060 I 75.80 - 90.87 o(s) - o(s) 2.55 o(l) - o(llr 2.65 95.14 0(r) o(5) 2.63 - o(3) 2.57 78.94 - o(2) 2.70 84.13 o(5) - o(3) 2.51 ao.77 s2. 30 o(6) - O(I) 2.63 83.78 o(7) - o(2) 2.64 92.06 - 0(6) 2.59 r 84.93 - o(5) 2.59 80.12 - o(z) 2.64 83.73 - o(L) 2.70 88.38 o(t) - o(5) 2.go 88.39 o(zl - o(z)r 2.76 96,74 O(2) - 0(6) 90.76 - o(4) - o(6) 2.79 o(a' - o(7) 2 .19 99.20 0(r) o(3) o(r) - o(s)r 2.A2 92.77 - o(3) 2.42 90.93 o(o) - o(e)r 89.71 97,1r r 95.88 - o(4) 2.54 - o(z) 2.A7 92.27 0(2) - O(1) 98.59 - 91.65 o(r) - o(4) 2.A6 o(4) - O(3) 92.47 O(3) 2.e9 - o(3) 2.93 roo.99 o(3) - o(?) 2.87 92,71 - 0(6) 2.46 o(s)r- o(q) 2.9O 97.13 - o(2) 2.97 9?.61 o(a)l- o(r) 2.84 95.40 I - o(6) 3.OO 92.53 o(o)l- o(r) 3.O2 lot. ro _ o(5) 2.95

- 365 M(1) - tir(5) 1.1(2)- M(5) c M(O) H(4) 3. - r,r(4) - n(s)t c 3.485

- M(4) c 3.493 I - M(5) 3.217 r(l) - ,r(l) e 2.888 u(4) - lt(5) e 2.994 H(5) - r(r)11 2.9S9 - r(u)r e 3.054

- u(5) e 3.3?l M(4) - il(4) c 3.963 - !{(4) 3.440 r - u(s) 3.468 r - n(a) 3.524 11 - u(s) 3.592 1l - 3.543 "(a)

degteee' *Stqtdard detiatiore fo" M-M, M-O and, O-o ate 0.004, 0.011 dtld 0.015 fl reapectioely od fon angle O-M-) 0.4

** e atd e refe" to qnen- and. edge-elured Li.nkagee. 36 GATEHOUSEET AL.: LOVER]NGITE

davidite REE landauite sodium loveringite calcium

Basedon this proposal,loveringite then qualifiesas a new member of the group, with calcium as the (i) ( ii) dominant large cation (Ketly et al., 1978). Fig. 3. (i) Represenrationof articulationof M(4)O",M(s)Oo, Acknowledgments and M(2\O, polyhedra between adjacent h-M-c layers in Wewish to thankDr. Henri-JeanSchubnel, Ioveringite.(ii) Basicstructural element in GanTi,O.,(Lloyd et at., MuseumNational t9'76). d'Histoire Naturelle, Paris,for kindly supplyinga sampleof moh- site (Le Plate Muratouse, La Grave, Hautes Alpes, , No. positionsfor daviditesamples, and consistentlyob- r03,s23). tainedbetween 35 and 36 oxygensper unit cell.Ifthe References compositionof loveringite sampleCl87-31 is normal- Bannister,F. A. andJ. E.T. Horne(1950) A radioactivemineral ized to 36 oxygens,we obtain ALs6MB.&Oru.This from Mozambique related to davidite. Mineral. Mag , 29, formulahas considerably less than 2l M cations.The I0r-tI2. above hypothesisis consistentwith the decreased Baur,W. H. (1961)Atomabst?inde und Bindungswinkelim Broo- kit, TiO,. Acra Cr.ystallogr numberof M cations;atoms in sitesM(2) andM(3) , 14, 214-216. Campbell,I. H. and P Kelly (1977)The bond to anionO(7), and of love- if O(7) is occupiedby cal- ringite. Mineral Mag , in press. cium,then sites M(2) andM(3) will beempty. How- -, G. J. H. McCalland D S.Tyrwhitt (1970) The Jimberlana ever,where a vacancyoccurs in anion siteO(7), site norite,Western Australia-a smalleranalogue of the Great M(3) maybe occupiedby ionswhich can adapt to the Dyke of RhodesiaGeol. Mag , 107, l-12. reducedanion coordination, six-fold - Gefler, S. (1960)Crystal structure of B-GarOs.J Chem.Phys., 33, five-fold.It is 676-684. apparentthat further structuralwork on daviditesor Grey,I. E. and D. J Lloyd(1976) The crystal structure ofsenaite. high-calciumloveringites is necessaryto clarify this Acta Crltstallogr.,832, 1509-1513. question. - snd B. M. Gatehouse(1978) The crystalstructure of Iandauite,Na[MnZndTi,Fe)rTi,r]O,r. Can. Mineral., in press. Systematicnomenclature of crichtonite-groupminerals andJ. S.White, Jr. (1976) The structure of crichto_ niteand its relationship to senaite.Am. Mineral.,6l,1203,-1212. A numberof mineralshave beenreported in the Hey, M, H., P. C. Embreyand E. E. Fejer(1969) Crichtonite, a literaturewhich all havethe same basic structure type distinctspecies. Mineral. Mag , 37, 349-355. as crichtonite,and similarcompositions. According Hornstra,J. and B. Stubbe(1972) PW ll00 Data processing to Strunz(1966), these are davidite, crichtonite, sena- Program,Philips Research Labs., Eindhoven. ite, and mohsite.In a recentcomposition Kelly,P., lan H. Campbell,lan E. Greyand BryanM. Gatehouse and struc- (1978)Loveringite, tural study,we find (port- [Ca,REE][Ti,Fe8+,Cr]r,Ose,a new mineral that the minerallandauite from Norseman,Western Australia. Can. Mineral.,in press. novet al.,1966)also fits into thiscategory (Grey and Kleeman,J. D. andJ. F. Lovering(1967) Uranium distribution in Gatehouse,1978). All theseminerals have trigonal rocks by fission-trackregistration in lexanplastic. Science, 156, symmetryand structuresbased on a close-packed- 512-5t3. Lacroix,A. (1901)Minbralogie anion latticewith a nine-layer(hhc. ..) stackingse- dela Franceet de sesColonies,yol. 3. LibrairiePolytechnique, Paris. quencealong the trigonal axis. This complicated Levy,A. (1827)On a newmineral species. pftl Mag, ser.2,I, stackingsequence is apparentlystabilized by the 22t-223. presenceof largecations in sitesin the cubic-stacked Lloyd,D. J., L E. Greyand L. A. Bursill(1976) The structureof anion layers,i.e. the largecations are the structure- GanTi2,Onr.Acta Crystallogr.,832, 1756-1761. determiningspecies, and we haveproposed Pabst,A. (1961)X-ray crystallographyof davidite.Am. Minera!, a nomen- 46,700-718. claturesystem for theseisotypic mineralsbased on Portnov,A. M. L. Ye Nikolayevaand T. I. Stolyarova(1966) A the dominantlarge cation in eachcase. This proposal newtitanium mineral, landauite. Doklady Akademii Nauk SSR, is in harmonywith the known compositionsof the t66.1420-1421. previously-namedminerals from the type localities, Shannon,R. D. and C. T. Prewitt(t969) Effective ionic radii in and resultsin the followingclassification: oxidesand fluorites.Acta Crystallogr, 825,925-946 Strunz,H. (1966)Mineralogische Tabellen,4th ed. Akademische Verlagsgesellschaft. Mineral name Dominantlarge cation Leipzig. crichtonite strontium Manuscrip!receiued, April 25, 1977;accepted senaite lead for publication,August I l, 1977.