Canadian Mineralogist Yol.29, pp. 87-93(1991)

STRONTIOWHITLOCKITE,SrrMg(PO3OH)(POr6, A NEW MINERALSPECIES FROMTHE KOVDORDEPOSIT, KOLA PENINSULA,U.S.S.R.

SERGEI N. BRITVIN, YAKOV A. PAKHOMOVSKII, ALLA N. BOGDANOVA aNo VLADIMIR I. SKIBA GeologicalInstitute, Kola ScienceCentre of the U.S.S.R.Academy of Sciencx,Apatity, U.S.S.R.

ABSTRACT par poids. La formule iddale serait donc SreMg(PO3OH)(POdo.Densit6 3.64(2) mesur6e, 3.60 Strontiowhitlockite, the Sr-dominant analog of whit- caicul6e,Le spectred'absorption infra-rouge montre des lockite, occurs in the Kovdor deposit, Kola Peninsula, bandesi 1090,1030, 955, 595 et 555cm-r. U.S.S.R.,within cavitiesin a dolomitecarbonatite vein that cross-cutspyroxenite. Aggregates are pipeJike, with radial (Traduitpar la R6daction) structurein cross-section,and are composedof rosettesof roundedcrystals tabular on {001}, asmuch as 8 pm across. Mots-cbs;strontiowhitlockite, nouvelle espbce min6rale, Associatedminerals are , plrite, collinsiteand an carbonatite,phosphate, structure de la whitlockite, unnamedSr-Mg phospate.Strontiowhitlockite is dull white, gisementde Kovdor, p6ninsule de Kola, U.R.S.S. transluscent,with a white . is moderateon {001}. It is opticaly uniaxial(-), with to 1.601(2),e 1.598(2) for \ = 589nm. By analogywith whitlockite, thp mineral INTRoDUCTION ig hexagonal,R3c, with a 10.644(9),c 39.54(6)A, Z 3880 At, Z = 6^.The strongestfive X-ray-powder diffraction Whitlockite was initially describedby Frondel lines[d in A(I)(/?k0] are s.33Q5)(ll0), 3.288(37X0.0.r2,2t4), (1941)and was interpretedto be naturally occurring 3.07I (29X030), I 0), 2.661(80)(220). Elec- 3.004(100X0.2. (Frondel Numerous investiga- tron-microprobeanalyses gave CaO 5.5, SrO 5l.4,BaO 2.3, B-Ca3(PO)2 1943). MgO 4.6, MnO 0.2, FeO 0.2, P2O535.2, H2O 0.5 (by tions since then have been devoted to both B- coulometry), total 99.9 wt.9o. The ideal formula is Car(POn)r,its isostructuralcompounds, and whit- SreMg(PO3OH)(POdo.Dn 3.64(2),Dc 3.60 g/cm3. The lockite. Studiesby Calvo & Gopal (1975),Schroeder infrared-absorption spectrumincludes rhe following bands: et al. (1977)and Moore & Shen(1983) showed that 1090,1030, 955, 595, and 555cm-l. whitlockite, ideally CarMg(PO3OHXPOJ.,differs from B-Ca3(PO)2.The mineral is relatedto a series Keywords; strontiowhitlockite, new mineral species,car- of isotypic compounds with the general formula phosphate, bonatite, whitlockite structure, Kovdor AyB(Xqn(XO? y)6(I,OH,F)3, where cations of deposit,Kola Peninsula,U.S.S.R. the.4 groupare iepresented by Ca2*,RE'E3+, Na*; the B group includesMg2*, Fd*, Fe3*,Al3*, x SovnernE may be p5+, gi4+ or Al3+, and YrepresentsO2-, OH- or F. All of theseisotypic compounds are syn- La strontiowhitlockite,analogue de la whitlockite avec thetic. cerite-(ce), 6sr+rpe3+(sio3oHXSio4)6 le Sr commecation dominant, a 6t€ d6couvertedans le gise- (OH): (Moore & Shen 1983) is the only other ment deKovdor, situ6dans la p6ninsulede Kola, U.R.S.S.; mineral isostructuralwith whitlockite. elle occupedes cavit6s d'un filon de carbonatitedolomiti The new species, strontiowhitlockite, que qui pyroxdnite. recoupeune Les agr6gatsde cristaux SreMg(PO3OH)(PO4)6,is defined as the Sr- allong6smontrent une texture transversaleradiaire, et con- dominant (in the,4 group) analogof whitlockite. It sistentde rosettesde cristaux arrondis aplatis sur {001}, et mesuantjusqu'd 8 pm enlargeur. Lui sontassocies dolo- was found in a specimenof dolomite carbonatitecol- mite, plrire, collinsiteet un phosphatede Sr-Mg sansnom. lected in the summer of 1985 from the Kovdor La strontiowhitlockite estblanc terne, translucide,avec une deposit,Kola Peninsula,U.S.S.R. Both the species rayr:reblanche. Le clivage{001 } estmoyen. Elle estuniaxe and the name have beenapproved by the Commis- n6gative,avec co 1.601(2), e 1.598(2)pour X = 589nm. Par sion on New Minerals and Mineral Names,I.M.A. analogieavec la whitlockite, c'est yn min6rallexagonal, (l-2 -- The holotype specimenof strontiowhitlockite R3c, aveca 10.644(9),c 39.54(6)A, Z 38804", Z 6. mg of the mineral) is preservedin the Fersman plus Les 1:inqraies les intensesdu clich6 de diffraction [d MineralogicalMuseum of the U.S.S.R. Academyof itA)(AcU I en sont s.33(25X10), 3.288(37)(0.0.r2,2r4), (registration no. 558)' and the 3.071 (29)(030), 3.004(1 00X0.2. I 0), et 2.66 I (80)(220). Les Sciences,Moscow analysesd la microsonde€lectronique ont donn6CaO 5.5, grain mount used for microprobe analysis is on SrO 51.4,BaO 2.3, MgO 4.6, MnO 0.2, FeO 0.2, P2O5 depositin the Museumof Mines, Institute of Mines, 35.2, H2O 0.5 (par coulom€trie),pour un total de 99.9q0 Leningrad. 87 Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/29/1/87/4005966/87_29_1_cm.pdf by guest on 29 September 2021 88 THE CANADIAN MINERALOGIST

OccunnsNcr after dolomite, including collinsite, bobierrite, vivianite (Kukharenkoet al,1965) and kovdorskite The Kovdor ultramafic alkalinecomplex, of Mid- (Kapustin et al. l98l\. dle Paleozoic age (338-426Ma), is located in the An interesting 60-m long vein of dolomite car- southwesternpart of the Kola Peninsula,U.S.S.R. bonatitethat cross-cutspyroxenites (jacupirangites) (67o35'N, 30o20'E),and is emplacedin Archean was exposedduring mining operationsin 1985and gneissesand granitic gneisses(1800-2000 Ma). The includesnumerous cm-size cavities involving phos- complex (40.5 km2) is elliptical in shapeand con- phates,mainly carbonatefluorapatite as well as col- centrically zoned (Kukharenko et al. 1965)from core linsiteand bobierrite.Strontiorvhitlockite (about 5-6 to rim; dunitesand "pyroxenized" and "phlogopi- mg of the mineral)was found in a cavity I cm across tized" dunitesin the coregive way to jacupirangites in the central zone of the vein, in associationwith and melteigites,melilite rocks, ijolites and other budlike aggregatesof strontian collinsite (6.3V0 nepheline-pyroxenerocks, and an outside ring of SrO), octahedralcrystals of pyrite and rhombohedra fenites. The Kovdor magnetite-apatite-baddeleite of dolomite. An unnamed Sr-Mg COr-bearing deposit is located in the southwesternpart of the hydrous phosphate(hereafter referred to as Sr-Mg complex;it is emplacedwithin contact of ijolites with phosphate)is intimately intergrown with the stron- fenites.In general,the igneousrocks exposedin the tiowhitlockite. quarry (the Iron mine) are forsterite-magnetite (with apatite)ore-rocks and pyroxenites(jacupirangites). PHYSIcALPnopnnrrss A variety of calcite-magnetite and dolomite- magnetiteores seem to be connectedwith a later, car- Strontiowhitlockite occursas pipes and roselike bonatite stageof formation of the deposit. Acces- aggregatescomposed of rounded tabular crystals sory baddeleiteis presentin both forsterite-magnetite (Figs. 1,2). Crystalsas much as 5-8 pm acrossare and carbonate-bearingores. flattenedon {001}. Aggregatesresembling pipes are Veinsof carbonatitecross-cut rocks and ores,and the most interesting.At high magnification (Fig. lb), are widespreadthroughout the deposit.The carbona- the pipes,up to 2 mm long and20 pm in diameter, tites can be dividedinto the following groups,based show a radial structure, suchthat the [001] axis of on mineralogical criteria (Krasnova & Kopylova each crystal is subparallelto the direction of pipe 1988): calcite carbonatites with forsterite and elongation. The inner channelsof the pipes are phlogopite, calcite carbonatiteswith ferriphlogopite, occupiedby "spindles" of the Sr-Mg phosphate, dolomite carbonatites with zircon, and calcite- which exhibit a hexagonalcross-section. dolomite carbonatiteswith ilmenite. Dolomite car- Strontiowhitlockite is white with a dull luster, bonatitescontaining zircon are of pertinencehere. translucent,and has a white streak. The hardness There is hydrothermal phosphate mineralization cannot be measured accurately owing to small

Ftc. l. Pipescomposed of strontiowhitlockitewith inner "spindles" composedof Sr-Mg phosphate.SEM image;width of field of view is 290 pm (A) and 40 pm (B).

Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/29/1/87/4005966/87_29_1_cm.pdf by guest on 29 September 2021 STRONTIOWHITLOCKITE FROM THE KOLA PENINSULA 89

crystal-sizeand compositenature. A moderate{001} cleavage(or parting) is present,and was observed by SEM. The measureddensity D. was determined by flotation of pipe fragmentsusing a dilute Clerici - H2Osolution, and found tobe3.64(2)g/cm3; D" is 3.60g/cm3. In immersionliquids, the mineral is colorlessand nonpleochroic. The axial character cannot be observeddirectly becauseof small crystal-size,but pipesof the mineral show strong parallel extinction under crossedpolarizers; the smallerindex of refrac- tion coincideswith [001]of the crystals.If thesedata are taken into accountalong with the fact that the mineral is isostructural with whitlockite, stron- tiowhitlockite should be uniaxial (-), with a coof 1.601(2)and a e of 1.598(2)for tr : 589nm. Using the Gladstone-Daleconstants (Mandarino 1979),the calculatedindex of compatibility is 0.012, indicat- ing "superior" agreementof optical, physicaland chemicaldata. Frc. 2. RoseJikeaggregates cor{rposed of strontiowhitlock- ite crystals.SEM image;wid]th of field of view is 15pm. CnysreLLocnepHy

The strontiowhitlockitecrystals are too small for phosphatewere performed on a CAMECA MS-46 single-crystal study, and only X-ray powder- instrument with wavelengt[r-dispersionspectrome- diffraction techniques were used. Synthetic 0- ters, usingthe following stafrdards:lorenzenite (for (Sr2.5tMgo.rr)":.oo(POJzwas preparedaccording to Na), diopside(Ca), celestine (Sr), barite (Ba),pyrope the method reportedby Sarveret ql. (1961)to com- pare its powder pattern with that of the mineral. Both (P). Instru conditions were: 20 patterns(Table l) wereobtained ulilizing a DRON-2 diffractometer,40 kV, 20 mA, 0.5ols, with graphite- current, 5 pm spot size. analysisis averaged monochromatized^Cul(aradiation. Oneextra reflec- usingl0 spots,l0-s countin[ time per spot,with l0 tion (d : 2.930 A, I : 25) attributable to Sr-Mg s spentcounting the . No otherelements phosphatecontamination was removed from the with atomic number than ll were detected, strontiowhitlockite pattern. It can be seenthat the powder pattern of the microprobe (Carl Zeiss I instrument). The mineral is closeto that of B-(Srz.srM9o.a:)r:.oo(POJzianalytical data were by use of an "in strontiowhitlockiteis relatedto this compoundin the house" program, and the are shownin Table same manner as are whitlockite and synthetic B- Ca3(PO)2(Gopal & Calvo 1972). is only Strontiowhitlockiteis hexagonal, R3c by analogywith whitlockite (Calvo & Gopal 1975). Sr. The powder pattern was indexedbased on initial cell- The determinationof watdr in the mineraland the par:rmetersof cerite-(Ce)(Moore & Shen1983); sub- interpretation of the data wlerecomplicated by the sequentleast-squares refinement (POLYCRYSTAL heterogeneousnature of ihe strontiowhitlockite program, Institute of Catalysis,Siberia Branch of aggregates.Using SEM images,the phasecomposi- the U.S.S.B.Academy of Sciences)gave a 10.644(9), tion of aggregateswas estirpatedto be as follows: c 39.54(6)A, r:AtOltO; A3 and Z : 6. Similar cal- - 80vol.9oofpipelikeaggregates, - 10vol.9oof culations for B-(Sr2.rrMgo.a:)r:.oo(Ppd2yielded a rosette-likeones and - l0 vol.9o of Sr-Mg phos- 10.606(2),c 39.37(l) A, V 3835(2)A3 and Z = 21. phate "spindles". Water (potal HrO) was deter- The relationshipbetween this compoundand stron- minedby microcoulometricrhoisture analysis on 0.85 tiowhitlockite is discussedbelow. mg ofheterogeneousaggregate. Two discreteevents ofwater lossare observed.The flrst, between70 and CHEMICALCoMPoSITIoN 120"C,centered at l00oc (- 1.5 wt.9o), seemsto representloss of molecular HrO contained in the An aggregateof the mineral was mounted and Sr-Mg phosphate.The secondweight-loss event, 0.5 polishedfor electron-microprobeanalysis. Quantita- + 0.2 wt,Vo,occurs between 410 and 570"C, with tive analysesof both strontiowhitlockiteand Sr-Me a maximumrate of dehydrationat 500'C; it is inter-

Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/29/1/87/4005966/87_29_1_cm.pdf by guest on 29 September 2021 90 THE CANADTAN MINERALOGIST

TABLE 1. X-RAY POWDEB-DIFF'RACTIONDATA FON preted as resulting from decomposition of the sTRoN?IowUITLocKITf, AND 8-(s!257Mfr.a3)23(poa)2 (PO3OH)2-group present in strontiowhitlockite. This temperatureis lower than that for both natural STBONTIOWIIITLOCKITE 8-(Sr257Mgb.a3)23(POa)2 and syntheticwhitlockites, T00 and 1000'C, respec- tively (Gopal et al. 1974),but this may be dueto the N 4ut S"b. I/Iobs !"rr" C"b" I/rob lower thermal stability of the strontiowhitlockite structure. ro4 6.?42 6.7L5 6.74 10 pipe-like of stron- txo 5.322 5.33 25 5.303 5.32 65 As noted above, aggregates 202 4.449 4.50 5 4.4?3 4.4A 10 tiowhitlockite are predominanu consequently,all the o1a 4.356 4.34 s 4.33a 4.35 11 1.O.10 3.634 3.633 I7 3.619 3.620 high-temperaturewater, 0.5 wt.9o, is addedto the 122 3.431, 3.437 3.4!9 3.420 60 204 3.354 3.361 30 total of analysis1. o.o. J-2 3.241 3.246 3? 2L+ 1'??l)r.,"u 3.274 300 3.073 3.0?1 29 3.062 3.062 50 DISCUSSION oF THE FORMULA o.410 3.OO1 3.OO4 r.oo 2.949 2.9B4 100 t2a 2.444 2.44! L7 2.437 2.836 32 306 2.745 2.775 2.774 35 Strontiowhitlockiteis ascribedto whitlockite-like 220 2.661 2.661, ao 2.652 2.651, 90 2.6I4 2.604 2.602 compoundsmainly on the basis of X-ray powder 226 2.464 2.+6L 2.454 2.462 6 In our usage,the term com- 2.O.L4 2.404 2.39A 2.395 7 data. "whitlockite-like 1.O.16 7 pounds" involvesisostructures of both whitlockite 3.O.I2 2.2341 ^ ^^^ :';:'" | 2.246 26 50 404 z.ztal "'"'o (Calvo& Gopal 1975,Moore & Shen1983) and 0- 2.494 2.!45 2.IA6 30 Ca3(PO)2(Sarver et ol. 1961,Dickens et ol. 1974, o.z16 2.L74 2.47L a 2.L69 o4a 2.081\ ql. 23 -'--", ^qn +o Schroederet 1977);all are derived from the o- 2:3ZZj2.084 2.o?5J 2.2.r2 2.O70 2.062\ ^ ^-^ Ba3(POa)2structure type. The crystalstructure of o- 324 2.O64 z.oerJ "'""' 37 Ba3(POa)2was solved by Zachariasen(1948). It is 1.1. 1A 2.O3r 2.034 a 2.O22 4.O.10 Leell 1 oo1 26 7.ea4 composedsolely of transitionally equivalentinter- 743 7.9a9 ) """ :':::, 55 238 L.937 I.93? 50 connectedrods (chains) consisting of PO, tetra- :'::i t r.s40 29 L.2.r7 r.927 hedra and BaO* polyhedra. There are two distinct s!6 L.924 7.922 17 1.917 1.914 +5 1.a5a 40 barium sites,Ba(I) and Ba(II). The Ba atom occupy- r.429 22 1.a30 25 LAO9 ing the Ba(I) site coordinatesto six nearby oxygen r.743 36 35 atoms Ba(I)O6-octahedron]and six more r.724 9 !.72L 15 [distorted 1A distant oxygenatoms; thereforeBa(I) has in total a r.664 5 LL l2-fold coordination. The Ba atom occupyingthe 1.604 10 1.600 27 Ba(II) site has l0-fold coordination. Every third Ba 7.594 1,4 L5s9 4 sitein the structureis Ba(I), the remainingsites being 1.536 3-2 L532 1.503 a Ba(II). The simplest repeat-unit along a chain is 4.495 7 L.494 9 POr-Ba(II)-Ba(I)-Ba(II)-POn. r 1a linaq +^ particular feature of this structure type is the d - rJ-?6 A instability produced becauseof a reduction of the cation radius (Gopal & Calvo 1973,Dickens et al, 1974), and becauseorthophosphates of divalent that of Sr2* do not TABI,E 2. CITBTICALCOMPOSITION OF S?RONTIOWHITLOCKI?E cations of radius smaller than AND THE StsMg PSOSPHATE adopt the cv-BaFe3(POa)2structure, but rather are derivative structures. In the caseof B-Ca3(PO)r, there is the loss of one in everyeight formula units per cell, in comparison with the "ideal" o- Na^O m.g o.o o.2 o.o Ba3(PO)2type; the remaining sevenunits are dis- 4.7 tributed in a nonrandom way. The structure of B- SfO 5r.4 5a.o 47.5 Ca3(PO)2thus contains a vacancy. BaO 2.O The of whitlockite, Mco 4.6 +.4 3.0 CaeMg@O3OH)(PO4)6and cerite-(Ce), REEnFe3 MnO o.2 o.1 " o.1 (SiO3OH)(SiOJ6(OH)r, of rods FeO o.2 0,2 are composed o.3 (chains) (Calvo & Gopal 1975, P^O- 35.2 34.+ 31.6 of two distinct types Hzo o.5 0.6 Lo.a Moore & Shen 1983).The repeatunit of rod II is TOTAL 99.9 101-4 100.0 quite identicalin both structuresand like that in a- Bar(PO)2; rod II is ordered and filled. However, * 6rlqulated ssming atomic raiio p3H - ?:1 the compositionof rod I is different in whitlockite By difrerence, ,including H2O *d CO2 s well and cerite-(Ce).In the structureofwhitlockite, rod 1. Strontiowhitlockite, pipe qggregate 2. Stronuowhitlockile, fose-like I is composed of randomly distributed 3. Sr-Mg phosphate, ,,spindles, MgCan(PO)2 and MgHr(PO)2 groups. As far as

Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/29/1/87/4005966/87_29_1_cm.pdf by guest on 29 September 2021 STRONTIOWHITLOCKITE FROM THE KOLA PENINSULA 91

cerite-(Ce) is concerned, there are tal chemistryof Sr2* and Mg2*. However, similar Fe3+(Sio3oHXOH)3groups distributedalong rod I insertion of Mg into Ca sites is known and was in a nonrandom way. Empty sitesexist along rod I studiedby Schroederet al. (1977),who refined the in both whitlockite and cerite-(Ce)structures. The crystal structure of Mg-containing B-Cat(PO)r. B- ratio of rod I to rod II is l:3. (Sr,Mg)3@Or),whitlockite-like compounds also are Crystallographic data for whitlockite and 0- known (Sarver et al. 196l), but no structure deter- Ca3(POa)2are quite similar: both compoundspos- mination was carried out. It is interestingthat pure sessR3c symmetry and have a hexagonalunit-cell Sr3(POa)2under normal conditions is an cv- containing 42PO4 groups, consistingof 6 formula polymorph, isostructural with cr-Ba3(POa)2 units of whitlockite or 2l formula units of (Zachariasen1948); p-Srr(PO), is stableonly above Car(PO)2; they are not distinguishableby an ordi- 1300'C (Sarver et al. 196l). In order for B- nary X-ray powder-diffraclion study @rondel 1943). Sr3@O)2 to stabilize under normal conditions, As to our case,a structuresolution for strontiowhir- there must be substitution of cationsof small ionic lockiteis not possiblebecause of the smallgrain-size, radius (e.9., Mg) for Sr. This is an essentialrequire- and consequentlythe questionexists as to whether ment for Sr3@O), to existin the whitlockiteJike0- the formula for whitlockite or that of Ca3(PO), is modification (Sarveret al. 196l). correct.As reportedby Gopal & Calvo (1972),care- Becausestrontiowhitlockite and cerite-(Ce)are iso- ful powder diffractometry may be usedto distinguish structural with whitlockite and are closeto the 6- whitlockite from B-Car(PO)2,but it is inapplicable Ca3(PO)2structure type, it could be expectedthat in our case,because a Sr-analogof B-Ca3(PO), is substitution Mg for Sr and of Fer* for Ce3*, known (Sarveret al. l96l), but an Sr-analogofwhit- respectively,may occur. However,one more expla- lockite is not. Thus, an X-ray powder-diffraction nation exists for excessMg and Fe. The crystals study does not solve the problem. may consistof domainsof two different but related If the chemical composition is considered,the structure-types. Relevant to this proposal, an microcoulometry shows the presence of high- interestingobservation was made by Sarveret al. temperaturewater (interpretedas hydrophosphate) (1961)on the 0-(Sr,Mg):(POJzcompounds. The in strontiowhitlockite. Sincethe hydrogenis shown intensitiesof X-ray reflectionson powder patterns to be an essentialconstituent of the whitlockite struc- decreasevery markedly as Mg content is increased, ture but not of B-Car(POn),(Gopal & Calvo 1972), and the compoundscontaining 20 to 30 mole %oof then the whitlockite-type formula is acceptedfor Mg3(PO)2 have only diffuse powder-diffraction strontiowhitlockite, requiring sevenP atoms (or a patterns. The authors suggestedthat this can be total of 28 oxygen atoms) per formula unit. attributed to the differencebetween the X-ray scat- The empirical formula of strontiowhitlockite tering factorsof Mg2* and Sr2*. But this could also (anal. I, Table2) calculatedon the basisof 28 atoms be attributed to a domain structure in the 0- of- oxygen, is: (Sru.r6Ca,.rrBa6.2,Mg,.6oMn2*0.*(Sr,Mg)3@Orrcrystals. + Fd 0.ot'lo.rHo.zrPo.xOzr.m.The sum of (Mg,Mn,Fe) As can be seen, it is not possible to give a is 1.68,and this is substantiallygreater than 1.00for simple explanation of excessoctahedral cations ideal whitlockite. There is a similar situation for in whitlockite-like compounds; future studies carite-(Ce)from the rare-earthdeposit at Mountain will reveal the correct explanation. For now, Pass,California (Glasset ol. 1958),where calcula- we have assumedthe most likely pattern of sub- tion basedon sevenSi atomsyields 1.55octahedral stitution of Mg for Sr in strontiowhitlockite: cations per formula. Moore & Shen (1983), who (Sr6.e6Ca,.36Mge.6sBq.21Mno.*Feo.*)"r.rrMBr.ooHo.zr refined the structure of cerite-(Ce)from Mountain P6.e6O2s.00ithe ideal formula of the mineral is thus Pass,suggested that the discordancewas a result of SreI\4g@O3OHXPOa)e. either the presenceof impurities (the natural material was analyzedby the wet-chemicalmethod) or addi- Ilrn'nanso-AnsoRprloNSpscrnoscopv tional structural sitesoccupied by octahedral cations (mainly Fe3+). In the caseof strontiowhitlockite, The infrared-absorption spectrumof strontiowhit- contaminationby impurities is unlikely becausethe lockite was obtained utilizing a UR-20 Carl Zeiss mineral wasanalyzed using an electronmicroprobe. spectrophotometer.Spectra also were obtained on However, the second possibility may apply to synthetic B-(Sr2.57Mgs.or)>:.oo(POJzand natural strontiowhitlockite. Additional octahedralcations whitlockite from the Tip Top pegmatite, Custer, may be introduced into vacant sites along rod I. South Dakota (Leningrad Mining Museum specimen Nevertheless,other suggestionscould be proposed number162l/l). About I mg of eachcompound was about the excessofoctahedral cations.Ofthese, the ground and pressedinto a KBr pellet, and the first is the possibleinsertion of Mg into Sr sites,in infrared-absorptionspectrum was recorded over the fact, substitution of Mg for Sr. This is an unusual region 400-3800cm-r (Fie. 3). suppositionbecause of an incompatibility in the crys- The strong absorption bands within the region

Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/29/1/87/4005966/87_29_1_cm.pdf by guest on 29 September 2021 92 THE CANADIAN MINERALOGIST

\--- 8400

r0901030

z 6 o oE z 1030 F 1090 ;e

-965 l140 -1000

1300 900800 WAVENUMBERS(crn-r ) Frc. 3. Infrared-absorption spectra of strontiowhitlockite with l09o Sr-Mg phosphateimpurity 14), synthetic 0- (Sr2.57Mg6.a3)s:.oo(POdz(B) and whitlockite (C).

ll40-930 cm-r are attributedto stretchingmodes of tals, compared with strontiowhitlockite and 0- POf- tetrahedra,and the absorptionbands ranging (Sr2.57Mge.o3)p:.oo(PO+)z, or a difference in crystal from 620 to 550 cm-r are attributed to bending syrnmetryamong Sr- and Ca-dominant members;X- modes of POl-. It is to be noted that the stron- ray singlecrystal$ are requiredto answerthis ques- tiowhitlockite aggregatecontains about l0vol.9o of tion. SomeCO2 contarned in whitlockite is revealed Sr-Mg phosphateimpurity. This would probably not by the 1490 and 1420cm-r bands. affect the position and configuration of the absorp- In conclusion,it will be noted that the absorption tion bands in the strontiowhitlockite spectrum. In bandsare affectedby Ca-for-Sr substitution.It can general, the spectra of the mineral and 0- be seenclearly with bendingmodes (620-550 cm-r) (Sr2.57Mg6.a3)p:.oo(POJzare very similar, indicating that this compositional shift is about 10-15 cm-r the structural similarity of these compounds. among Sr and Ca end-members. However, the spectrum of strontiowhitlockite includes a weak additional band attributed to CO.2- Sr-Mg PuosrHarn anions(1470, 1420 and 870 cm-r) and bondedwater (3400and 1620cm-t). Theseconstituents cannot be The spindlesof Sr-Mg phosphateare too thin essentialin the mineral becausethe analyticaltotal (about l0 pm in diameter)and their quantity is too is about 100 wt.qo (anal. l, Table 2). Thus, we sparsefor a proper study to be carried out. As far believethat CO2 and H2O can be attributed to the as the chemicalcomposition is concerned(anal. 3, Sr-Mg phosphate. Table 2), the ratio of the cationsmay be represented The spectrumof whitlockite also is similar to the as: (Sq.2,Ca,.:zBfo.zJx.ra$g1.s7Fq.6tMn6./',tft.m. spectraof Sr-dominant compounds,but there is a This formula is much like that of the whitlockite more obvious multiple splitting of the bands. This structlue-type. However, the low analytical total could meaneither the perfectionof whitlockite crys- comparedto that of strontiowhitlockite showsthat

Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/29/1/87/4005966/87_29_1_cm.pdf by guest on 29 September 2021 STRONTIOWHITLOCKITE FROM THE KOLA PENINSULA 93

these are distinct compounds. The sharp phase- -, -, Iro, J. & SantNn,W.K. (1974):Crys' boundary betweenthe minerals (Frg. lb) also pro- tal structure of synthetic Mg-whitlockite, vides evidenceof this. It is possiblethat strontiowhit- CalsMg2H2(POo)1a. Con. J. Chem. 52, 1155-1164. lockite and the Sr-Mg phosphateare closelyrelated structurally. Karusrn, Yu. L., Bwova, A.V. & Puoovrtre, Z.V. (1981): Kovdorskite, a new mineral. Zap. Vses. Mineral. Obschest. 109, 341-346 (in Russ.). ACKNowLEDGEMENTS KnasNova,N.I. & Kopvrove, L.N. (1988):Geological We are grateful to AssociateEditor EugeneE. basefor realization of mineralogical-technological Foord and two anonymousreferees for their reviews mapping (the Kovdor deposit)..Izu. Akad. Nauk Ser. of this paper, including helpful suggestionsfor Geol. 5,8l-92 (in Russ.). improving the English. Dr. N.A. Yelina of the Geo- logical Institute of the Kola ScienceCentre per- KurHannNro, A.A., Oorova, M.P., Burex, A.G., formed the microcoulometricwaler analysis.We also BAcoesaRov,E.A., Rimskaya-Korsakova,O.M., A.S. & thank LeningradMining Museum Nephedov, E.I., Ilyinsky, G.A., Sergeev, colleaguesof the (1965): Complex of provided Abakumova, N.B. Caledonian for the specimenof whitlockite for this Ultrobasic Alkaline Rocks and Carbonatites of the study. Kola Peninsula and Northem Karelia. Izd. "Nedra", Moscow (in Russ.). RBr'BnnNces MANnenrNo, J.A. (1979): The Gladstone-Dale rela- Carvo, C. & Goear, R. (1975):The crystalstructure tionship. III. Some general applications. Cor. of whitlockire from the Palermo quarry. Am. Mineral. 17, 7l-76. Mineral. 60, 120-133. Moonn, P.B. & SuaN, J. (1983): Cerite, DrcrENs,B., Scrnonnrn,L.W. & Bnowr, W.E, (1974): REe(Fe3+,Mg)(SiOr6(SiO3OHXOH)r: its crystal Crystallographicstudies of the role of structure and relation to whitlockite. Am, Mineral. as a stabilizingimpurity in B-Car(PO/r. I. The 6E, 996-1003. crystalstructure of pure B-Ca3@O)2.J. Solid State Chem.10,232-U8. Senven, J.F., HorrvaN, M.V. & Hutr,tuel, F.A. (1961): Phase equilibria and tin-activated lumines- FnoNou-,C. (1941):Whitlockite: a newcalcium phos- cence in orthophosphate systems. J. Elec- phate,Ca3(POiz.Am. Mineral. Xi, 145-152. trochem. Soc. 10E, ll03-lll0. (1943):Mineralogy ofthe calciumphosphates ScHnororn, L.W., DtcrcNs, B. & Bnowx, W.E. (1977): in insular phosphaterock. Am, Mineral. 2E, Crystallographic studies of the role of magnesium 215-232. as a stabilizing impurity in p-Car(PO/r. II. Refine- ment of Mg-containing B-Ca3@O)r. J. Solid State GI-,css,J.J., EveNs,H.T., Jn., Cemor, M.K. & Hn-- Chem, 22,253-265. DEBRAND,F.A. (1958):Cerite from MountainPass, SanBernardino County, California. Am. Mineral. ZacHannsrN, W.H. (1948): The crystal structure of 43, 460-475. the normal orthophosphates of barium and stron- tium. Acta Crystallogr. l, 263-265. GorAL,R. & Carvo, C. (1912):Structural relationship of whitlockiteand B-Ca3@O)2. NaturePhys. Sci. 23707), 30-32.

& - (1973): The structure of Ca3(VO/2. Received February 26, 1990, revised manuscript Z. Kristallogr. 137, 67-85. occeptedJuly 15, 1990.

Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/29/1/87/4005966/87_29_1_cm.pdf by guest on 29 September 2021