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/<o.orlr.sr Br.os Sil2. The structure,which 14030. study of the mineralogy of the Mont Saint-Hilaire is isotypicwith that of osumilite,was refined to R : 3.090, two members of the osumilite and is orderedwith K in a [2]-co-ordinated C-site,Na in alkaline complex, octahedrally co-ordinatedA site, B in tetrahedrally co- group havebeen identified: milaritg and $e new spe- ordinated 72 site, Si in tetrahedrallyco-ordinated 71 site, ciespoudretteile (pronounced:PU-DRETIT). and the B site is vacant. There arepresently thirteen mineral speciesin the osumilitegroup; theseoccur in a variety of geologi- Keywords: poudretteite, new mineral species,osumilite cal environments.Merrihueite, roedderiteand yagiite group, Mont Saint-Hilaire, borosilicate, structure are found in meteorites, Eifelite, osumilite and refinement. osumilite-(Mg) are associatedwith volcanic rocks or SovvnrnB high-temperature contact-metamorphic aureoles. The remainder of the group, armenite, brannock- On a d6couvertla poudretteite, nouvelle espdcemin6rale, ite, darapiosite,milarite, poudretteite(present study), dans la carrihre Poudrette, au mont Saint-Hilaire (Qu6bec). sogdianiteand sugilite, are found in alkali-rich rocks On la retrouvedans une enclavede marbre dansla sy€nite such as syenites,alkalic granitesand calcite veins. ndph€linique,associde a pectolite, quartz, apophyllite, et This diversity in chemistry and geological environ- aegyrineen traces.Les prismeshypidiomorphes, 6quidi group mensionnels,transparents, et incolorese rose pale attei- ment make the interesting. gnent 5 Inm. Elle estcassante, de duret€environ 5, et montre Grew (1982)described osumilite as an important unecassure en 6cailles.Densit6 2.51(l) (mesurde),2.53(caJ- rock-forming mineral. Hemingway e/ al. (1984)have cul6e). Les cristaux sont uniaxes positifs, co 1516(l), e studied its thermodynamic properties. Structure 1.532(l). Sym6triehexagonale, groupe sparialP6/mcc, a refinementsof severalof the specieshave been per- 10.239(l),c 13.485(3)A, Z:2. Lesdix raiesles plus impor- formed, andternf et al. (1980)described the crys- tantesdu clich6de poudre [den A(t)(hkt)l sont: 6.74(30) tal chemistryof milarite in detail. (002), 5.13(1m)(110), 4.07(30X1 12), 3.70(3q(n4, 3.369(30) Poudretteiteis named in honor of the Poudrette (004), 3.253(100x211), 2.956(40)(300), 2.815(60X114), family, which operatesthe Carridre R. Poudrette, 2.686(50)Ql3,2M),et 2.013(30)(321).L'analyse d la micro- Mont Saint-Hilaire,Rouville Co., The name sonde€lectronique a donn€(90, en poids):SiO277 .7 , B2O3 Quebec. 11.4,K2O 5,2, Na2O6,2, total 100.5,d'oir la formule and mineral descriptionhave been approved by the empiriqueK1.6s(Na1.67K9.04)El.9t83.0jSil2.l4030, La struc- I.M.A. Commissionon New Minerals and Mineral ture, affinde d un r6sidu R de 390, est isotlpique de celle Names.The type material comesfrom this quarry; de l'osumilite. Elle est ordonnde;le potassiumoccupe la it comprisescotypes NMNS #51743 and NMNS 763 764 THE CANADIAN MINERALOGIST #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 <t ing curve. This indicates that within the 3o 002 6.74 6.74 3 008 t.686 1.@2 3 'lI 02 5.37 5.38 <l 414 1.678 experimentallimits of precision,this atomic site is l0 5.12 5.13 l0 421 r.663 200 4.43 4.43 <l 316 1.659 1.662 3 fully occupiedby boron, which compareswell with 1l2 4.08 4.07 <l 3 'll8422 t.626 1.627 202 3.70 3.70 3 1.601 t.600 l the electron-microproberesults. Grice e/ ol. (1986) 004 3.371 3.369 3 415 1.572 1.572 3 211 3.252 3.253 l0 334 1.522 1.522 <l advocatedthis method as a reliable chemicalana- r04 3.151 3.154 2 326 t.508 <l 300 2.956 2.956 4 218 1.506 506 lytical technique for boron in the description of lt4 2.816 2.815 6 308 1.464 465 2 213 2.&1 q23 2.686 5 425 t.423 3 moydite, (Ca,REE)[B(OH)4]CO3. 204 2. ffi4 228 i.408 407 <l 22D 2.560 2.557 522 I .389 389 <l 310 2.459 2.462 515 I.371 37t 2 3l l 2.419 2.421 523 1.354 222 ?.393 2.389 604 1.353 X-Rav CnvsreLLocnepuv 214 2.377 6n I.345 I .345 312 ?.3t0 2.310 524 1.308 1.306 304 2.222 2.223 r't.10 I .304 313 2.157 2.151 613 1,295 I .295 X-ray precessionphotographs show poudretteite il6 2.058 2.059 440 1.290 I .280 321 2.011 2.013 530 1.267 to be hexagonalwith possibleSpace-groups P6/mcc 314 I .987 1 .988 700 1.267 I .266 4t0 1.935 1.936 614 1.255 I .255 or P6cc, Resultsof the crystal-structurerefinement, 4lt t.9'15 1.912 821 1.224 1.225 216 1.867 622 1.210 I.210 2 presented below, establish the space group as 412 1.860 1.858 338 1.199 323 1.853 444 1.197 1.198 I P6/mcc, The unit-cell pilameters were refined from 3t5 I .817 t.818 428 1.188 I .187 I 306 1.739 I.790 623 1.186 X-ray powder-diffraction data obtained with a 500 1.773 1.773 114.6-mm-diameterDebye-Scherrer camera with {l-flltered Cutrcradiatlon; celi dloenslonsa 10.239(11,a 13.485(3)[ CuKo (Ni-filtered) radiation (Table l).