Canadian Mineralogist Vol. 25, pp.763-166(1987)
POUDRETTEITE,KNarB3Si12O3e, A NEW MEMBEROF THE OSUMILITEGROUP FROM MONT SAINT-HILAIRE,OUEBEC, AND ITS CRVSTALSTRUCTURE
JOEL D. GRICE, T. SCOTT ERCIT AND JERRY VAN VELTHUIZEN Mineral SciencesDivision, National Museumof Natural Sciences,Ottawa, Ontario KIA 0M8
PETE J. DUNN Departmentof Mineral Sciences,Smithsonian Institution, Washington,D.C, 20560,U,S.A.
Assrnact positionC d coordinanceXII, le sodium,la position,4d unecoordinance VI, le bore,la position72 ir coordinance Poudretteiteis a newmineral species from the Poudrette IV, le silicium,la position71 i coordinanceIV, etla posi- quarry, Mont Saint-Hilaire,Quebec. It occursin a marble tion B estvacante. xenolith includedin nephelinesyenite, associated with pec- tolite, apophyllite, quartz and minor aegirine.It forms clear, Mots-clds: poudrettdite, nouvelle espbce min6rale, groupe colorlessto very pale pink, equidimensional,subhedral del'osumilite, mont Saint-Hilaire, borosilicate, affi ne. prismsup to 5 mm. It is brittle, H about 5, with a splin- mentde Ia structure. tery fracture;Dmetr. 2.51(l) g/cml, D"6".2.53 g/cm3. Uniaxialpositive, co 1.516(l), e 1.532(l).It is-hexagonal, spacegroup P6/ mcc, a I 0.239(l), c 13.485(3)A and,Z : 2. INTRoDUcTIoN The strongestten X-ray-diffractionlines in the powderpat- tern [d in A(r\(hkDl are: 6.74(30)(002),5.13 (100)(110), The optical and physical propertiesof members 4.07(30)(r 12), 3.70(30)(202), 3.3 6e(30)(004), 3.253 ( I 00) of the osumilite group are similar to those of com- (2r r), 2.9s6(40)(3 00), 2.8 I 5(60)(I I 4), 2.686(50)(213,204) mon mineralssuch as quartz and cordierite;for this and 2.013(30)(321).An analysisby electron microprobe reason, they are probably generally overlooked. gave:SiO2 77.7,B,2o311,4,K2O 5.2, Na2O 6.2, sum 100.5 However, it is becomingmore evident that the group wt. q0 yields , which the empirical formula is quite widespreadin occurrence.In an ongoing K1.jn(Na1.s/
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#51791, deposited in the National Museum of no apparentcleavage; it has a splintery to conchoi- Natural Sciences,Ottawa, and a cotype at the Smith- dal fracture. The density,measured with a Berman sonian Institution, Washington, D.C. (NMNH balance and temperature-corrected,is 2.51(l) #163776).To date, sevencrystals are known, each g/cm3, which agreeswell with the calculateddensity a few millimetres in size. of 2,53g/cm3. Poudretteiteis uniaxial positive, with indices of OccunnsNcn refractionr,r 1.516(l) and e 1.532(l),measured with sodium light (gel-filtered,tr 589.9nm). The mineral There is extensiveliterature on the mineralogy and displayssharp extinctions and a sharp uniaxial figure geology of the alkali gabbro - syenitecomplex at with no biaxial distortions,as are observedin many Mont Saint-Hilaire, one of the ten Monteregian specimensof milarite. Hills. This virtually linear seriesof monadnocksrises abovethe platform of the Saint LawrenceLowlands CHEMICALCoMPoSITIoN betweenOka and Megantic. The recent field-trip guidebook of Mandarino et al. (1986) contains a SpecimenNMNH #163776was analyzedwith an descnptionof the geologyand mineralogyof Mont ARL-SEMQ microprobewith operatingconditions Saint-Hilaireand a comprehensivelist of references. of 15kV, samplecurrent 25 nA (measuredon brass) The study specimenswere collected from the and a focusedbeam. The following standardswere .quarry in the mid 1960sby M. JacquesBradley. used: volcanic glass (Si), microcline (K), and syn- Poudretteiteoccurs in the marble xenoliths within thetic plagioclase, Ana6 (Na). Specimen NMNS the nephelinesyenite breccia, associatedwith pec- #51791was analyzedfor boron with a JEOL 733 tolite and apophyllite, and with minor aegirine. microprobeoperating at 5 kV, 100nA (measuredon Milarite was found in this assemblageas well, but a Faraday cup), 40 s collection time, using lead not as a direct associateof poudretteite. ste€nateas the artalyzing crystal and a defocused beam (40 pm). Synthetic Ni3@O3)2was used as a Puvsrcal ANDOPTTcAL Pnopsnrres standardfor B. Poudretteiteis very stableunder the electron beam; cathodoluminescencewas not Poudretteiteresembles anhedral qtrartz, and it can observed.Beryllium and lithium were sought but not be confusedwith associatedapophyllite. It is color- detectedby ICP and AA, respectively. lessto very pale pink and transparentwith a vitre- The chemicalanalytical data are: SiOz77.7,B2O3 ous lustre; it has a white streak, and shows no 11.4,BeO 0.0, Li2O0.0, K2O5.2, NarO 6.2, sum fluorescencewith either LW or SW ultraviolet light. 100.5wt.9o. Basedon 30 oxygen atoms, this gives Crystalsare roughly equant, deeplyetched, barrel- the empiricalformula K1.66(Na1.rtlft.6a)21.e1B3.65Si12.1a shapedprisms measuring up to 5 mm. Poudretteite Ore. This is very close to the ideal formula is relativelyhard (Mohs hardness-5), brittle, with KNa2B3SirtO3s,which would have the correspond- ing chemicalcontent: SiO2 77.15, B2O3 11.18, K2O 5.04, Na2O6.630/0. In the structureanalysis of poudretteite,the site- TABLEl. PoUDRmSITE: X-RAY-DIFFRAcTIoil0ATA occupancyfactor of boron wasrefined. It converged dobs tobs dobs tobs to an occupancyof 94Q)s/owith the boron scatter- '1.740 100 8.87 8.90 2 324 1.742 Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/25/4/763/3446453/763.pdf by guest on 30 September 2021 POUDRETTEITE, MEMBER OF THE OSUMILITE GROUP FROM MONT ST.HILAIRE 765 unit-cell parametersand volume arci o 10.239(l), c TA8LE2. PoUDRETTEITE:STRUCnjRE-REFINEIENT DATA 13.485(3)A and V 1224.3(4)A3; Z=2. Ideal Fomula: (NazB:5lrzOao to.zs:(t) Space Group: fi/naa "(A):o(U: 13.503(4) RsrrNsN4sNroF THECnysraL Stnucruns zt2 I/([!):1229.4(a) Rad/Mon: lio/grapfl te No. of Fot 784 !: 9.8m' No. of F;>2.5d(J): 638 Experimental l.lJn. transnission: 0.630 Flnal a(obs.) | 3.0, I'lax. transnisslon: 0.705 Flnal.au(obs.): 4,3 A crystalfragment chosenfrom the type material n=r(lrol- lrcl)/:lrol (NMNS #51743)was ground to an ellipsoidmeasur- Prdxw(lFo I - IFc I)'?/xwlFo l'zAw=o-2(Fo) ing 0.30x0.30x0.45 mm. This crystalgives a dis- tinct uniaxial interference-figureand sharp, single diffraction-maxima on precessionphotographs. In- tensity data were collected on a fully automated Nicolet R3ru four-circle diffractometer using the method of Grice & Ercit (1986).The data relevant TABLE3. P0UDRETTEITE:FOSITIoML AfiD THERI'IAL PAR$IFIERS given to the structure refinement are in Table 2. u(€q)rl0r i? Structure refinement ( (c) i0 0 1t4 177\41 [6(A) 1l/3 2t3 1t4 r48(5) B (T2) 0 112 1/4 80(12) For the structurerefinement of.poudretteite, st(n) 0.05952(6) 0.3376r(6) 0.rr 333(4) 65(2) the 0l 0.0821(3) 0.3921(3) 0 r42(e) atomic co-ordinatesof.milarite (Aern! et ot. 1980) 02 0.1092(2) 0.2820(2\ 0.r333(r ) 133(6) 03 o.r!04(2) 0.47r0(2) 0.1873n) e2(5) were used. Refinementof positional and isotropic thermal parametersgave residual indices R:5.590 and R* = 6.4q0.When the thermal parameterswere refined anisotropically,the residualindex dropped to 3.090,and with the weightingscheme incorporat- ing an isotropic, primary-extinction correction, 1STE 4. PGJORENEIE: ilISONOPIC TftPEUIURT.FACTORS (XIONR") R*=3.3V0. The final positional parametersand sre u(eq) equivalent isotropic temperature-factorsare given in K (c) rs(s) 164(5) 2s(8) 0 0 8212) 177\4) Table 3, and the anistropic temperature-factorcoeffi- ila(A) los(6) r05(6) 235n1) 0 0 52(3) r 4€(5l B (rz) e3(r8) 8r(r3) 70(16) 0 0 47(9) 80(r2) cientsare givenin Table 4. Bond lengthsand angles si(Tt) 62(3) 74(3) 60{3) -6(2) 212') 36(2) 65(2) 0t 225112) r550r) 54(9) 0 0 103(10) 142(9) given D2 ilo(7) rs6(8) r65(8) -33(7) -17(6) 9r{6) r33(6) are in Table 5. The observedand calculated 03 e7(6) 104(7) 1117) -29(5) r2(5) 5r(6) 92(5) structure-factorshave beensubmitted to the Deposi- tory of UnpublishedData, CISTI, National Research Council of Canada, Ottawa, CanadaKIA 0S2. DrscussroN IABLE 5. POUDRETTEIEI SELECTEDTNTERATO'IIC DISTAXCES(g) AND ANGLES (C' The discoveryof the new mineral speciespoudret- K (C-slte) polyhedron teite leadsto a new seriesof possibleboron-bearing K-02 3.000(r) xl2 specieswithin the osumilitegroup, of generalstruc- Na (A-slte) octahedron vBxtCvtArwlI2)3rv(f tural formnla l)uo30. Boron, a Ia-03 2.378(1)X6 03-Na-03t6 108.0(0) difficult element to analyzefor, particularly in low 03-03 3.247(3)X3 concentrationsor when 03-03 2.346(3)X3 03-Na-03X3 86..l(l ) only small amountsof sam- 03-03 3.849(3)x6 03-Na-03X3 -9tr359.1(l ) ple are available,probably eludesmany researchers. nean Perhapssome of the chemicalanalytical problems B (T2-sJte) ietrahedron encounteredto date in analyzing osumilite-group 1.47312)X4 03-B-03X2 109.8(r) 03-8-03X2 il3.r (r) minerals are a result of unanalyzedboron. For ex- 03-03 2.411(4)X2 03-B-03X2 r05.5(r) 03-03 2.458(3)X2 nean IOl'.7 ample,as little as I .7 wt.9o B givesrise to I .5 atoms 03-03 2.346(3)X2 (on the basisof 30 oxygenatoms) in the ideal for- nean ZqitS' mula of osumilite, which would make it the Sl (Tl-slte) tetrahedron sr-ol 1.612(r) 0l-si-02 r09.8(r) dominant tetrahedrallyco-ordinated element in the si-02 1.61 3(2) 0l-si-02 1r0.5(1) 72 site. sr-02 1.621(21 0l-st-03 il0.5(l) sr-03 ]41(2) 02-st-02 104.3(1 ) Boron in the Z2 site hasa short nean t.0ru 02-sl-03 r09.8(1 ) ^characteristically 02-sl-03 111.8(1) B-O bond distance(1.473 A) as co^mp.aredto the 0l-02 2.638(3) mean IOE]' 0l-02 2.65612\ same site in milarite (Be-O 1.643 A (Cern! et ol. 0r-03 2.633(21 02-02 2.553(3) 1980),osumilite, Al-O 1.762 A (Brown & Gibbs 02-03 2.622131 03-02 2.662(2) l^969),synthetic magnesian merrihueite, Mg-O 1.955 dean 2-sn A lfnan et al. lg72) and sugilite, Li-O 1.971 A Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/25/4/763/3446453/763.pdf by guest on 30 September 2021 766 THE CANADIAN MINERALOGIST (Kato & Miura 1976).This tigtrt tetrahedronhas a Gnnw, E.S. (1982): Osumilite in the sapphirine-quartz mean O-O distanceof 2,405 A. The BO, tetrahe- terrane of Enderby Land, Antarctica: implications dron sharesone short edge(O-O distanceof 2.346 for osumilite petrogenesisin the granulite facies. A) wittr the Na octahedron,which distorts it con- Amer. Mineral. 67. 7A-781 . siderably. (1986): The .B crystallographicsite is normally at least Gnrcr, J.D. & Encrr, T.S. The crystal structure of moydite. Can. Mineral. 24, 675-678. partly filled in many osumilite-group minerals by Na (or or H2O both). Cerri, et al. (1980)observed that -, VeNVsrrHUtzEN,J.V., DuwN,P,J., Nnwnunv, "natural milarites with uniaxial optics seemto be D.E., Erz, E.S. & NrsneN, C.H. (1986):Moydite, confined to compositionswith high alkali, Be and (Y,R.EEI[B(OH)4](CO), a new mineral species H2O contents", which would require the B site to from the Evans Lou pegmatite, Quebec. Can. be almost fully occupied. However, poudretteite has Mineral. 24,665-674. a vacantB site, yet is still uniaxial. Thus the reason for uniaxial yersasbiaxial characterin this mineral Hruncwav,8.S., Ronrc,R.A., Krrrnrcr, J.A., Gnew, (1984): group still requires further investigation. E.S., Nelru, J.A. & LoNooN,D. The heat capacitiesof osumilite from 298.15 to 1000K, the thermodynamic properties of two natural chlorites ACKNowLEDGEMENTS to 500 K, and the thermodynamic properties of peta- The authors thank Dr. Frank Hawthorne for lite to 1800K. Amer. Mineral. 69,701-710. allowing them to usethe single-crystaldiffractome- ter at the Departmentof Earfh Sciences,University Kero, T. & Mrune, Y. (1976): Crystal structure of sugilite. Mineral. J. E, 184-192. of Manitoba. Mr. Bob Gault provided assistance with the electron-microprobeanalysis at the National KueN, A.A., Baun, W.H. & Fonaes, W.C. (1972): Museum of Natural Sciences.The critical reviewsby Synthetic magnesianmerrihueite, dipo{assium pen- Drs. Howard T. Evans, Jr. and John M. Hughes tamagnesium dodecasilicate: a tetrahedral mag- were appreciated. nesiosilicate framework crvstal structure. Acta Cryst. 82E, 267-272. RrrsnsNcrs MaNoanrNo,J.A., CHao, G.Y., Gaulr, R.A. & Heno, Bnown,C.E. & Grnns,G.V. (1969):Refinement of the R.K. (1986): Mineralogy and petrology of Mont St- crystalstructure of osumilite,Amer. Mineral. 54, Hilaire, Quebec. Geol, Assoc, Can., Mineral. Assoc. l0l-l 16. Can., Can. Geophys. Union, Field Trip Guidebook 9A. tnnt,l.f, P., HawruonNE,F.C. & JenosswrcH,E. (1980):Crystal chemistry of milarite.Can. Mineral. Received January 14, 1987, revised manuscript accepted lE. 41-57. April 3, 1987. Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/25/4/763/3446453/763.pdf by guest on 30 September 2021