WILUITE, Gars(Al,Mg,Fe,Ti)

1301

Thz Carwd.ian M ineralo gist Vol. 36, pp. l30l-13M (1998)

WILUITE,Gars(Al,Mg,Fe,Ti)13(B,Al,!)5Si1sO6s(O,OH)ro, A NEWMINERAL SPECIES ISOSTRUCTURALWITH VESUVIANITE, FROM THE SAKHA REPUBLIC, RUSSIANFEDERATION

LEE A. GROATI

Depamnent of Earth anl Ocean Sciences, University of British Columbia, Vancouver, British Columbia V6R 124

FRANKC. TIAWTHORNE

Departmcnt of Geological Sciences, University of Manitoba, Winnipeg, Manitoba R3T 2N2

T. SCOTTERCIT andJOEL D. GRICE

Mineral Sciences Division, Carudian Museum of Nanre, Onatva. Ontario KlP 6P4

AssrRAcr

Wiluite, Cale(At,Mg,Fe,Ti)13(B,A1,E)5SirrOes(OH,F,O)ro,rerragonal, a 15.752(L),c ll.7l7(l) A, V ZgOl.Z(Z)A3, space grotpP4lnnc,Z = 2, is a newmineral species of thevesuvianils g'.up from theWilui River,SakhaRepublic, Russian Federation. Itoccunasholosymmsfficcrystalswithforms(100Jand{101}dominantplusrninor{110}and{001},upto3X3x5cm, slightly elongatealong [001]. f{6 fiTvinningwas observed. Wiluite is darkgreen with a colorlessstreal<, a vitreousluster, and it doesnot fluoresceunder long- or short-waveultraviolet lighr It hasa Mohs hardnessof 6, is brittle with an irregularfracture, and haspoor cleavageon { 100}. The measureddensity is 3.36(3)glcm3, and the calculateddensity is 3.358g/cm3. In transmitted light, vdluiteis colorlessand nonpleochroic; it is uniaxial-positivewith a = 1.721(2)and e = 1.725(2).The strongestten reflections in the X-ray powder-diffractionpattern ld(in A)(I)(hkDl are2.'176(100)(342),2.617(61)(252),2.491(61)(260), 2.s92(43)(224),r.66(26)(346), r.640(23)(292),2.r21(20)(r3s),3.s2(r8)(240), 1.987(1sxs6r),2.929(14)(004), and 2.912(14)(233).An analysisof wiluite gaveSiO236.Ll, A12O312.03, TiO2 0.80, MgO 6.48,FeO l.21,Fezo32.28,CaO35.54, Ce2O30.18, BzO: 3.06,F 0.50,H2O 0.61, O = F 4,24, sum= 99.20wt.Va.Ttie concentrarion of FeOwas determined by wet chemistry,and that of H2Owas determinedwith a LECO induction furnace;the concentrationof the other elementswas deter- minsd fy electron-microprobeanalysis. The correspondingunit formula,based on 19(Ca+ Ce), is (Ca1s.97Ceo.o:)>rs (Al6r3TiffoFes6N4ga.s1Fe5s)p13(B2.63A1s.511.sa)z5Sirz.qsOoe[(OfDz.oso7.r]>ro. Wiluite is isostructuralwith vesuvianite,and con- tainsessential B [B > 2.5 apfu (xoms per formulaunit)]; vesuvianiteis uniaxial (-), wiluite is uniaxial(+). It occurswith grossularand serpentineminerals in a serpentinite.The namerecalls the localiry, and has beenin use as a varietal name for "vesuvianite"from this locality for over 200 years.

Keywords:wiluite, new rnineralspecies, electron-microprobe analysis, X-ray powder-diffractiondat4 vesuvianite,boron min- era1,Yakutia. Russia-

Sopnaene

Nous d6crivonsla wiluite, Cale(Al,Mg"Fe,TDr3@,Al,E)sSilaOoe(OH,F,O)ro,t6tragonale, a 15.752(1),c ll.7I70) A, V 2907.3(3)A3, groupe spatial P4lnnc, Z= 2. commenoun"au membre du groupede la v6iuvianiteprovenant de la rivibreWilui, enR6publique de Sakh4 F6d6ration Russe. Elle sepr6sente en cristaux holosym6triques montrant les forrnes dominantes { 100} et {101},etenplus, {110J et {001}moinsimportantes;ils atteignentunetaillemaximumde3 x 3 x 5 cm,etsontl6gerement allong6ssur [001].Aucune macle n'a€t€ d6cel€e.La wiluite estvert fonc6avec utre ra]ure incoloreet un 6clatvireux. Elle ne montreaucune fluorescence en lumibreultra-violette, soit en ondeslongues ou courtes.Sa duret6 est de 6; elle estcassante, et fait preuved'une fracnue irr6gulibre et d'un pidfe clivagesur { 100}. La densit6mesur6e est de 3.36(3), et la densit6calculde, 3.358 g/cm3.En fumi|1g6an5mise, la wiluite est incoloreet non pl6ochroique;els s51uniaxe positive, avec o = 1.72I(2) et e = 1.725(2).Les dix raiesles plus intensesdu spectrede diffractionX td(enA)(IXrftDlsoat2.776(100)(342),2.617(61)(252), 2.49r(6r)(260),2.592(43)(224),1.66(26)(346),r.&O(23)(2e2),2.r2r(2o)(r3s),3.52(18)(240),1.987(rs)(s6r),2.929(r4)(0M), et2.9l2(14)Q33).Une analyse chimique de la wiluite a donn6SiOz36.lI, AlzOg12.03,'tiOz 0.80, MgO 6.48,FeO 1.21,FezO:

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2.28,CaO35.54, Ce2O30.18, B2O33.06, F 0.50, HzO 0.61,O = F 4.24, pour un total de 99.20Vaparpoids. La concentration de FeO a 6€ d6termin6e par voie hnmide, et la teneur enHzo a eG 6tablie au moyen d'un four tr induction LECO. Le niveau de concenmdon des autres6l6ments a€t€Atabh,pat microsonde dlectronique.La formule chimique qui en resulte, fond6e sur 19(Ca + Ce), est (Ca16.e7Cee.e3)21e(,{16.53Tie.3eFes6Mga.8lFe50)>13(B2.63Ale.53n1.ea)>5silz.eeo6s[(OH)z.olOr.g7]>10.La wiluite est isostrucnrale avec la v6suvianite, et contient le bore comme constituent essentiel (>2.5 atomes de B par unit6 formulaire). La vdsuvianite est uniaxe (-), tandis que la wiluite est uniaxe (+). On trouve la wiluite avec le grossulaire et des min6raux du groupe de la serpentine.lans une serpentinite. Le nom rappelle la localit6, et sert ddja depuis plus de 200 ans pour signifier lavari€t6, de '!6suvianite" provenant de cet endroit. (Traduit par la R6daction)

Mots-clCs: wil'uite, nouvelle espdcemin6rale, analysed la miqosonde 6lectronique,diffraction X sur poudre, v6suvianite, minfpl de bore, Yakoutie, Russie.

INrnopucnom cal sector zoning; {001 } sectorsshows a cross-hatched pattern,possibly due to twinning, and the {110} and It has long beenknown (Jannasch1884, Widman { 100} sectorsshow fine striations.The {001 } sectorhas 1890,Jannasch & Weingarten1896) that vesuvianite a low birefringence and is slightly biaxial, withO <2V can containsignificant boron. Groat et al. (1992) < l0o; the { 100} sectorshave higher bireftingence, and showedthat vesuvianite samples from severallocalities 2V vaies within the range l0 < 2V < 25" . The to and e containhigh (>1 vrt.VoBzO) contentsof boron. Groat indices of refraction of the {001 } sector in monochro- et al. (1994) examinedthe mechanismwhereby boron matic light (590 nm) are 1.721(2) and 1.725(2),respec- is incorporatedinto vesuvianite,and showed that boron tively. The compatibility index is 0.008: superior. occupiestwo newly identifiedsites in the structure.If Boron-free and boron-poor vesuvianitesare uniaxial (or the occupancyof one or more of thesesites by boron slightly biaxial) negative. The composition (i.e., B con- becomesdemin2a1, then a newmineral species is estab- tent) at which the optic sign changesis not known, but lished.Vesuvianite from theWilui Riverhas long been the optic sign is a simple indicator of high-B vesuvianite known to have a high boron content,and the work of and wiluite. Groatet al. (1994)showed that vesuvianitefrom this localitycontains sufficient boron to establisha newspe- Cmvucer CowosrnoN cies.The new mineral is namedwiluite, a"fterthe locality, theWilui River,Sakha Republic (Yakutia), Russian Crystals were analyzedchemically with aJEOL733 Federation.The new mineral and mineralname have electron microprobe operating in wavelenglh-dispersion been approvedby the InternationalMineralogical As- mode with an acceleratingvoltage of 15 kV and a speci sociationCommission on New Mineralsand Mineral men current of 25 nA. Data on standards were collected Names.Type material is depositedat the Canadian to O.25Voprecision or for 25 seconds,whichever was Museumof Narure,Ottawa" Ontario, Canada. less. Data on each element were collected to 0.5Vopre- cision or for 50 seconds.The beam size was 10 or PHvsIcar Pnopnnrms 20 Um, and counting t;mes on peak and background, 20 and 10 s, respectively. The following standardswere Wiluite occursas isolated holosymmetric crystals up used: diopside (Si), almandine (Al,Mg,Fe), titanite (Ti), to 3 X 3 ( 5 cm (ll a, b, c, respectlely).The dominant tephroite (Mn), gehlenite (Ca), elbaite @), glass 5-254 formsare {100} and {101},with minor {110} and (Ce) and fluororiebeckite (F). The FeO content was de- {001}; no twinningwas observed. Wiluite is darkgreen termhed by tihation. The H2O content was determined with a colorlessstreak and a vitreouslusler; it doesnot with a LECO induction furnace. Data were reduced us- fluoresceunder longwave or shortwaveultraviolet light. ing conventional ZAF techniques. The mean of twenty- It is brittle with a poor cleavageon {100}, and as an five determinations is given in Table 1; the crystals are irregular fracture and a Mohs hardnessof 6. The den- chemically homogeneous. The chemical formula was sity wasmeasured with a Bermanbalance using toluene calculated on the basis of 19 X cations (= Ca + Ce), as at29"C;the measured density is 3.36(3)g/cm3, and the recommended by Groat et al. (1992); the resulting for- calculateddensity is 3.358g/cm3. mula is given in Table 1. A simplified formula may be written as Cale (Al,Mg,Fe,Ti)t, (B,Al,n)s Sire Oos Orncar Pnopsnrms (O,OH)1e.

In transminedlight, wiluite is colorlessand non- Trn Lnrmrnc B Covrem oF WLUTTE pleochroic.Although morphologicallytetragonal, wiluite shows"anomalous" optical properties in cross- As shownby Groatet al. (1994,1996),8 occupies r/+] r/+1/+ r/+] polarizedlight (Groater al. 1993).There is strongopti- the Z(l) [ 0.055,0.055, atdT(2) [ sitesin WILUITE FROM YAKUTL!\. RUSSIA 1303

TABLE1. cHEMICALoOMPoSITION' (wt.%) diffractometry showed the crystal tohave lmmtnLate ANDUNI-I FORMULA (eptu) FOR WILUIE symmetry; furthermore, the extinction conditions are sioz 36.11 Si 17.99 compatible with P4lnnc space-grolp symmetry. Details Alro, '12.03 of the refined crystal-structure are given by Groat et al. lto, 0.8 (1994), and the polarized ffiared spectrum is given by Ir/gO 6.48 AI 0.53 Groat et aI. (1995). FeO 1.21 tr 1.U Fe.O. 2.28 OccuRnm,tce arvo Assoqnrsl MweRAI-s CaO 35.54 Ce2O. 0.18 AI 6.53 Wiluite occurs associated with grossular in a matrix BrO, 3.06 II 0.3 of fine-grained serpentine minerals, carbonate, Fe$ 0.86 limonitized pyrite, chlorite and "achtarandid', a teta- HrO 0.61 Fe2* NA pseudomorph of rrnknown precursor mineral O"F 4.24 lr/S 4.81 hedral an from the Wilui River region, Yakutia, Russia (Grew rotal T 994_ 1996), tentatively identified as wadalite (Galuskina et Ca 18.97 al. 1998). The association suggests that the primary 0.03 minsl4l assemblagewas that of a skarn that was subse- : 10

OH 2.03 TABLE 2. X-MY POWDER DIFFRACTION 7.97 DATA FOR WILUTTE E 10 ld d*(A) d*(A) h k t

' 5 5.86 5.86 00 Na, Cl not detested 4.7 4.7 o2 5 4.04 4.O4 22 4 3.94 3.94 04 the vesuvianite-typestructure. In the structuralformula 18 3.52 3.52 24 of wiluite, thereare four T(l) sitesand one Z(2) site, 5 3.27 5.27 04 A summingto a total of 5 Z sitesper formula unit. Ideally, 3.02 3.02 24 14 2.929 2.929 00 only oneofthese sites needsto be morethan half-occu- 14 2.912 2.912 23 pied by B to give rise to a new mineralspecies; thus 100 2.7t8 2.775 34 there are four potential end-membersinvolving the 7 2.701 2.701 - - sites:T(l) rQ) !; Z(1)= I, T(2)= B; (1) = B, 61 2.617 2.617 25 T(2)=f;7]Q)=7121= B. However,some of theresult- 4il 2.592 2.592 22 ing speciescan only be idenffied via crystal-struchre 11 2.524 2.525 13 refinementto deriveB occupanciesof theT(1) ndT(2) 61 2.491 2.491 26 sites.This is obviouslynot practical.Hereo we define 7 2.451 2.452 05 gonteining 7 2.55 2.35 o4 wiluite as >2.58 apfu,such thatthe (l) and 2.325 2. 25 14 T(2) sites have an aggregateoccupancy of greater o 2.3 2.3 33 than0.5. I 2.228 2.228 17 The correspondingend-member formula for wiluite 13 2.147 2.147 46 is asfollows: 20 2.'t2'l 2.12 13 8 2.1 2.1 Care[Al5Mg8] B5 (Si1sO6s)O1s. 10 2.069 2.068 37 2.046 2.047 46 X-Rav Drnrnasnou b 2.0s7 2.037 37 o 2.012 2.012 36 lc 1.987 1.988 The powder-diffractionpattern (Table 2) for a bulk 12 1.779 '1.773 17 samplewas recordedon a SiemensD5000 diffract- 26 t.oo t.oo s4 ometeroperating at 40 kV and30 mA, usingBaF2 as an 29 1.64 1.U internal standard.Cell dimensionswere refined using 1.634 1.634 08 ',t.624 30 reflections (CuKo1 radiation), and are given in I 1.624 25 Table2. o 1.591 1.591 Single-crystalprecession photographs (lr4oKo X-ra- I 1.568 1.568 66 I 6EO I 660 16 diation) indicatetetragonal symmetry. Very careftrlex- aminationof extinctionconditions and Laue symmefr'y Refined unit€llbassd on 30 rsflections: on precessionphotographs and by single-crystal a15.7521m, c 11.7169(9)A. 1304 THE CANADIAN MINERALOGIST quently serpentinized, altering all of the skarn minerals Gnoer, L.A., HAwTHoRNE,F.C. & Encrr, T.S. (1992):The except wiluite and grossular.The mineral is widely dis- chemistryof vesuvignite.Can. Mineral.30, 19-48. tributed in both institutional and private mineral collec- (1994): tions worldwide. & - The incorporation of boroninto ttrevesuvianite structue. Can. Mineral.32, 505-523. Orrnn Locarnres & PuNs, A. (1993):The Groat et al. (1992, 1994, 1995) reported chemical symmetryof vesuvianite.Can. Minzral. 31,617-635. compositions for several samples of B-bearing "vesuvianite'0.In fact, the following additional locali- LAcER,G.A., Scnur-rz,A.J. & Encrr, ties contain wiluite: Templeton Township, Oftawa T.S. (1996):X-ray and neutroncrystal-structue refine- boron-bearingvesuvianite. Can Mineral. 34, County, Quebec (Groat et al. 1994), and Bill Waley ments of a mine, Tulare County, Califomia (Groat et al. 1996). 1059-1070. Several other localities reported by Groat et aI. (1992, Rossuar, c.R. & ERcrr,T.S. (1995): 1994) hav e B-bearing vesuvianite. Theinfrared spectroscopy ofvesuvianite in theOH region. Can. M irc ral. 33, 609-626. AcmowIl,DGEIvEJ.ns Jmwnscl P. (1884):ZwKenntniss derZusammensetzung des We thank Peter l.eavens and George Robinson for Vesuvians.Neucs Jahrb. Mincral. Geol.Palaeont.,266- their comments on this manuscript. Financial support 270. for this work was provided by Natural Sciences and Engineering Research Council of Canada grants to LAG _& WuNcanreu, P. (1896): [Jber die chemische and FCH. Zusammensetzungund Konstitutiondes Vesuvians und des Wiluits. Z. Arcrg. Chem-ll,4048. RrnennNcrs WIDMAN,O. (1890): Mineralanalytiskameddelanden fran Upsala kemiskalaboratorium. GeoI. Fdren. Stockholm GALUSKtrIA,I., Gnrusrn, E. & Srrenz, (1998): M. AtoII Fdrlu lZ7,2O-29. hydrogarnetsand mechanismof the formation of achtaranditepseudomorphs. Neues Jahrb. Mineral., Monntsh,49-62.

Gnsw,E.S. (1996): Borosilicates (exclusive of tourmaline)and boron in rock-forming mingrals in metamorphicenviron- Received June 9, 1998, revked manwcript accepted Auqust ments.Rey. Mfueral. 33. 387-502. 23. 1998.