181 The Camdian M ineralo gist Vol.35,pp. l8l-187 (1997)

SHELDRICKITE,A NEW -.FLUOROCARBONATE MINERALSPECIES FROM MONT SAINT.HILAIRE, OUEBEC

JOEL D. GRICEI, ROBERT A. GAI]LT ANDJERRY VAN YELTHTIIZEN

ResearchDivisio4 Canadian Maseutn of Naurq P,O.Box 3443, Sation D, Ottatna,Ontario KIP 6P4

ABSTRACT

Shel&ickite, ideally NaCa3(COr)zFtHzO,is a newly identified mineral qncies from Mont Saint-Hilaire, Quebec.It occurs as an aggregateof blocky, colorlessto white crystalsup to 2 mm wide, with individual crystalsup to 0.1 mm, and as aggregates of silky white flakes to 2 mm asross.Associated minerals include , shortite, , polylithionite, arfuedsoniteand minor molyMenite. The mineralhas a vitreousto silky luster and a white steak" It is soft (Mohs hardness3) and brittle, with an unevenfracture and good {001} parting. Sheldrickrjeis uniaxial positive, co= 1.538(2)and e = 1.563(4).It is trigonal, space group Au a 6.718Q), c 15.050(4)A" y 588.3(3) 43, arrdZ = 3. The strongestseven X-ray powder-ditfractionlines [d in A Q)@tAl are:5.809(30X100),5.010(30)(003), 3.3s8(30)(110), 2.791(s0)(113), 2.s08(40)(006), 2.010(100)(116) and 1.939(40)(3ffi).The infrared spectrumis given. Threeelectron-microprobe analyses and a thermogravimetricanalysis gave Na2O 9.1'6(9.IL-924), Cao 48.84(48.6249.1r, Sro 0.36(0.33-0.40), F 16.17(15.91-1652),CO225.81and HzO 5.61,O = F -6.81, total99j4 vtt.Vo.COz was calculaGdby stoichiometryfrom the resultsof the crystal-structureanalysis. The empirical formula basedon l0 anionsis Nar.01(Ca2ezsr0.0t)D.m(Co:)zfFzs0(OlDo.silv.nH2Oor, ideally, NaCadCodfzEzO. Dcdc. = 2.86 elcu3 and Dmeas.= 2.86(4, g/cm3.The structurehas beenrefined to R - 4,6Vousing a twinned crystal. The structue is layeredon (001). One layer consistsof (COr)} groupsoriented perpendicular to (@1), the Naqa polyhedraand the HzO groups.A second layer consistsof Caggpolyhedra and F- anions.The structureof sheldrickitebears little resemblanceto the chemically similm rouvilleite, but it seemsto be a modiflcation of the sffucturesof bastnHsiteand cebaite.The namehonors Georse M. Sheldrick creatorof the SHELX software,widely usedfor the refinementof crystal structures.

Keywords: sheldrickite,new mineral species,carbonate, crystal structure,twinning, Mont Saint-Ililaire, Quebec.

Sovuens

Nous d6cdvonsla sheldrickite,nouvelle esp&e mindrale de compositionid6ale NaCa3(CO)zFyHzO,provenant du mont Saint-Ililaire, Qudbec.On la trouve en agr6gatsde cristaux fappus incolores ou blancs atteignant2mn, av?.cles cristaux individuelsjusqu'i 0.L mm en longueur,et en agr6gatsde flocons soyeuxjusqu'i 2 mm de diamdtre.Lui sont associ6spectolite, shortite, microcline, polylitlionite, arfredsonite,ainsi que molyMdnite accessoire.La sheldrickiteposs0de un 6clat vitreux e soyeuxet unerayure blanche. Elle estmolle (dwet6 deMohs 3) et cassante,avec une ftacture in6gale et un bon plan de sdparation {ml}. Elle est uniaxepositive, ro = 1.538(2)et e = 1.563(4).Il s'agrtd'un min6raltrigonal, groupe spatial P3z, a6.718(3)-, c 15.050(4)A, y 588.3(3)Az et Z = 3. Les septraies les plus intensesdu clich6 de dififtaction (mdthodedes poudres) [d en A (4(rr*01sont s.809(30X100),5.010(30)(003), 3.358(30)(110), 2.791(50)(113), 2.508(40)(006), 2.010(100)(116) et I .939(40)(300).Nous l'avons caract6risdpar spectroscopiedans I'infra-rouge. Trois analysesI la microsonde6lectonique et une analyse thermogravim6triqueont donn6 Na2O 9.16 (9.1L4.2A), CaO 48.84 (4.6249.15), Sro 0.36 (0.33-0.4), F 1.6.17 (15.91-16.52),CA225.8L et H2O 5.61,O = F -6.81, totzl 99.L4Vo(en poids).Nous avonscalcul6 la proportionde CO2par sto6chiometie selon les rdsultatsde la d6terminationde la structurecristalline. La formule empfuique,fondde sur une basede 10 anions, est Na1.s1(Ca2.eSre.61)p.es(CO3)zfFz.s0(OfDo.mln.n.Woou, de fagon id6ale, NaCa3(COj2F3.H2O.La densit6 calcul6eest 6galei 2.86, et la densitdmesrnde, 2.86(4). Nous en avonsaffrnd la structurejusqu'e un r6siduR de 4.6% avectm cristal macl6; elle montre descouches dans le plan (001).Une couchecontie,lrt des groupes (CQ)} perpndiculaires i (001), les polyddresNaq6, et les groupesH2O. Une secondecouche est faite de polyBdresCar6 et d'anionsF-. La sauctureressemble peu i celle de la rouvi1l6ite,qui lui ressemblechimiquemen! mais semble8te une modifrcationde celles de la bastniisiteet de la cebalte.Le nom honore GeorgeM. Sheldrick, cr6aGurdes logiciels SHELX, dont I'utilisation est r6panduepour I'affinement dessf ucturescristallines. (Traduit par la R6daction)

Keywords: sheldrickite,nouvelle espdce min6rale, carbonate, sfiucture cristalline, macle, mont Saint-Hilaire,Qu6bec.

1 E-mnil address:[email protected]

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INrR.oDUcrroN with individualsup to 0.1 x 0.1 X 0.1 mm, and (2) more commonly as radiating thin white silky flakes to Mont Saint-Hilaire is known throughoutthe world fibrous massssup to 2 mm 1pide.These two habitswere for its diveisityin mineralspecies. At this locality,41 car- establishedas the same speciesby X-ray diffraction, bonateminerals have been identified (Horv6th & Gault infraxed spectroscopy,and elechon-microprobedata 1990), as well as ten undescribedspecies (Cbao aal. The mineral is colorlessto white, with a white sreak 1990).Of the carbonateminerals, 16 contain the rare- and vitreousluster. It is brittle with an unevenfracture, earth elements(REE) as essentialconstituents (Grice andhas a good {001 } parting. Sheldrickiteis relatively 1996),30 containessential Ca or Na (or both), andnine soft (Mohs hardness3) and does not fluoresce. The containesse,ntial F; most of the fluorocarbonatescontain density, measuredby displacementin toluene, is the REE. To date,there are only two known Na{a-F 2.86 t0.M g/cm3,which comparesvery well with the carbonateminerals, rcuvilleit€ (McDonald et al. L99L)afi calculateddensity, 2.86 glcm3. sheldrickite.both of which occur at Mont Saint-Hilaire. Sheldrickite is uniaxial positive, to = 1.538(2) mineral The new describedhere, sheldrickite, found ande= 1563(4)(for l, = 589 nm), andnonpleochroic. A originaly in the Poudrettequarry, Mont Saint-Ililairc, Gladstone-Dalecalculation gives a compatibility index Rouville County,Quebec, is namedin honorof hofessor of 4.M4, which is regardedas superior (Mandarino (L942-), George M. Sheldrick Institute for Organic 1981). Chemistry, University of Giittingen, creator of the SHEI)( seriesof programsnow usedby many crystal- Cuwrcel ColvposmoN lographers.The newestversion SHELK-93 contains a routine for refining structuresof twinned crystals. Resolutionof this structureand subsequentdescription Chemicalanalysis was donein wavelengfhdispersion (WD) microprobeusing of this new mineral were dependentea this program. mode on a JEOL 733 electron Datareduc- The new mineral and the name were unanimously TracorNorthern 55@ and 5600autromation routine in the approvedby the Commission on New Minerals and tion was done with a conventionalZAF programs. Mineral Names,IMA. Cotypematedd is housedin the TracorNorthem TASK seriesof The operafing collection of the CanadianMuseum of Nature, cata- voltagewas 15 kV, and the beamcurrent was 0.20 trrA. loguenos. CMNMI81530, CMNMI81537, CMNMI Three points were analyzedon a single grain using a 81538and CMNM 81539. beamdiameter of 50 pm. Therewas no 4pparenlchemical zoningusing the back-scatterelechon detector. Data for OccunnnccE all elementsin the sampleswere collectedfor 25 s or 0.507oprecision, whichever was auainedfust. A 100-s Mont Saint-Hilaireis an alkaline intrusive comFlex energy-dispersionscan indicated no elementswrth Z and oneof the ten MonteregianHills, a seriesof plutons greater than 8, other than those reported here. The aligned along the St. Lawrence Valley for almost presenceof CO2 and H2O was confirmed by inftared 150 km eastwardfrom Oka to Megantic. The cotype specffoscopy,and the proportion of H2O was estab- specimenswere collected in 1991 by Canadian lished by thermogravimefricanalysis. Standards used Museum of Nature staff and by a private collector, for the electron-microprobe analysis were: G. Haineaull At present sheldrickitemust be consid- (CaKo), albite (NaKcl), celestine(SrZcr) and synthetic ered a very rare mineml, as there are only approxi- NalLaz(COg)iF (FKcl). Data for standardswere col- mately 60 mg known to exist. The specimenswere lected for 50 s or O.25Vopreciion, whichever was collectedin the Poudrettequarry from a marblexenolith attainedfirst. The chemicalcomposition (with ranges) in nephelinesyenite, close to a large unit ofhornfels. is NazO 9.16 (9.1,1.-9.24),CaO 48.84 (48.6249.L5), Sheldrickite is intimately associated with shortite, SrO 0.36 (0.33-{.40), F 16.17 (15.91-L6.52),CO2 Na2Ca2(COt3,the crystals being found in a cavity 25.81and H2O5.61, O = F -6.81, total99.14 wt.Vo; betweenshortite crystals and as flakes in thin seams the proportion of CO2was calculatedby stoichiometry betweencrystals of shortite. Other associatedspecies from the results of a crystal-structure analysis (see include pectolite, microclineo polylithionite, arfved- below). The empirical formula based on 10 anionsis sonite,aeghine, polylithionite, calcite, and mi- Na1.s1(CaaeSre.oJz.ss(CQ)2[F2.s0(OtI)0.02]2.e7'H2Oor, nor , leucosphenite, , ideally, NaCa:(COr)zFa'HzO. , , , schairerite and The thermogravimetricanalysis of sheldrickitewas .This mineral assemblageis thoughtto be a done using a Mettler - Toledo TA8000 system(soft- late-stagehydrothermal infi [ing. ware version 3.0), which usesa Mettler TG50 module liaked to a Mettler M3 microbalance.We used dry PHYSICAL AND OPTICAL PROPmf]ES nitrogen as the purge gas, with a flow rate of 200 ml/min. T\e 2.528 mg sampleof flaky material Sheldrickitehas two distinct habits: (1) it occursas a was ground to a fine powder and heatedfrom room 1 X 1 X 2 mm aggregateof blocky twinned crystals, temperatureto 350"C at a rate of 5"C min-l. The

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o

6 g

wsmbq(m-r)

Ftc. 1. Inftared spectrumof sheldrickitefrom a portion of a blocky crystal.

weight loss of 0.142 mg occurred in one continuous X-Rev Cnvsterrocnepnv exp stepbetween 160" and 265"C. This weight loss repre- Cnvsral,-Srnuc"ilins DsrERvm{ATIoN s€nts5.61 wt-%o,wlichagrees very well with that calcu- lated from the results of the crystal-structureanalysis hecessionphotographs show sheldrickiteto be hex- (5.49tttt.Vo). agonal, diffraction symmetry 6lmm.rn,with possible space-groupchoices P622 andP6422.With the solu- IMransD SpscrRUM tion of the crystal sfructure,it becameapparent the ftue symmetryof sheldrickiteis ffigonal, spacegoup P32e and the pseudohexagonalsymmety is due to merohe- The hfrared spectum of sheldrickitewas obtained dral twinning. X-ray powder-diffractiondata, obtained using a Bomen Michelson MB120 Fourier-fiansform with a Gandolfi camerahaving a diarneterof 114.6mm infrared spectometer with a diamond-anvil cell as a and using CuKa radiation,are given in Table t. microsamFling device. Two sampleswere analyzed; part of a blocky crystal @ig. 1) and part of the flaky material. The two specta varied only in the details of the fine stucture in the bandsfor the asymmetricand symmehicsfretching of the [CO3]group. The spectrum TABIJ L SEEII,RICXIIT! X-nAY POWDn DIFIRAC:IION DATA has sharp peaks,with a spttting of the bands, [CO3] 4b 4&(A) &A rn; 4e(A) d.rdA) hkt indicative of a structure with more than one crystal- lographically distinct [CO3] group (this was shown to 30 J.809 5.811 100 <10 1.1?5 lJ23 3M 30 5.0t0 5.016 003 <10 1.674 1.672 009 be the casein the crystal-structuredetermination). The 30 3.35E 3.359 110 l0 1.652 1.653 216 infrared specfrum can be compared to that of rou- <10 2.851 2.856 201 <10 1.613 1.613 310 50 2.19L 239t 113 <10 1.594 1.512 223 villeite, which has a very similar composition, <10 2.1t3 23t3 '!2 l0 1.535 1.534 3(E Na3Ca2(CO3)3F(McDonald et al. l99L). The notable ,f0 2.508 2.508 @6 1.536 3Lj <10 2.302 2.30t 204 <10 1.496 1.496 119 differencein the two specta is the absenceof the G-H 2.303 106 l0 1.396 1.395 225 and H2O bands. The absorption bands (cm-l) in 2n 2.199 2.t9 210 <10 1.356 1.357 316 l@ 2.010 2.w9 116 <10 1.332 1.331 219 sheldrickiteare assigned as follows: 3376: G-H stretch- 2.0L4 2r3 <10 1.267 126 309 ing; 1687: H2O bending; 1464: asymmetic stretching iO 1.939 r.939 300 <10 1.252 1,252 224 1.899 2M <10 1.231 1,230 413 modeof [CO:]; 1083:symmetic sfietchingof [CQ]; <10 r.898 1.878 302 >10 1.184 1.185 229 885 and 863:out-of-planebending of [COr];715 and 704: l0 1.809 1.E09 303 in-planebending of [COa]. The 628 cm-l band could 114.6 m catrdol8 amsa, CuKo ndldo4 yieully escioed not be unequivocallyassigned. l'4ddd6, ltrdodng bqsd @ th6 €Il a = 6.71t(3), c = 15.050(4) A

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TABLE 1 STIEI.DRICKIT& DATA{OIJJICTION TMORMAI.IoN

Spawcoup n2(#145) Msuedrcflwtiom 3895 @@@@@ o(A) 6X26(2) M€rg€dFflecliG 1205 c (A) 15,M4(4) obwedefl*rioB P 5o(Dl M7 v(ia 5s9.7(3) Mhimmtrami$i@ o344 @@@W@ Radiati@ Mofc Muimm trumissioo 0.606 M@chrcmdor Gmphite Refircdpam€tm 140 p1m''1 224 Re/o) 4,6 @6p@@W@ffi Unitsu @nterts 3[NaCa3(Cq)rF3 . HrO] 4p@p

For theintensity-data measurements, a crystal fragment W of cotypesheldrickite was used. Information relevant to the data collection and structure determination are given in Table 2. Reductionof the intensity data sruc- a& @ ure determinationand initial rcfinementof the sfucture were done with SHELXTL (Sheldrick 1990) package of computerprograms. @6 Phasingofa setofnormalized structure-factorsgave a mean value lE2- ll of 1.124.,indicative of a cento- symmeu'ic space-group,which is in contast to the @@ space groups derived from precessionphotography. Attempts to solve the structure in the spacegroups P6222 and P6a22 resultd in residual factors between @@ R= 4lVo andR = 297o.T\e combinedfigure of merit (CFOM) for severalspace groups in both the nigonal F-\ andhexagonal systems indicated a preferencefor space group 822L. The phase-normalizedstucture-factors 4p v were used to grve an E-map that located the two Ca sites, a iy'a site, and sevenlighter-element sites. This model refined ts R = 76Vo,but could not be improved. @@ ln particular,the (CO3)groups could not be located,and --j some O sites had unusual coordinations.The space- l- b groupsymmety wasreduced to P32.This did not rcduce the R factor, but it improved the model, such that one Ftc. 2. The structure of sheldrickite projected along [(D]. (CO3)group was located. The next stagein the structure Dark trianglesrepresent (CO:) polyhedra,large unshaded groups, determinationinvolved incorporatingatwin law forthe circles, H2O large light-shadedcircles, F atoms, small ligbt-shaded circles, Na atoms, and small dark- intensity data program (G.M. using the SHEIXI-93 shadedcircles, Ca atoms. Sheldricbunpubl data).Application of a twin by reflec- tion on (C{)1)immediately improved the model; it led to the location of the other (CO3)group and reduction of the R index to 7.9Vo.In the final least-squares refinemen! all atomic positions were refined vrith anisotropic-displacementfactors to a final residual Figure 2, but attemptsto refine the sfructure in this R= 4.6Vo.Bond-valence calculations (Brese & spacegroup gavean R index of 187o. O'Keeffe 1991) helped establishthe F and H2O sites. Table 3 containsthe final positional and equivalent The addition of an isotropic-extinctionfactor did not isotropic-displacementparameters and bond-valence improve the results.Inverting the polarity of the struc- sums, and Table 4 contains selectedinteratomic dis- ture resultedin R = l2%o,indicating the correctorienta- tancesand angles. Anisotropic displacement factors and tion. The structurewas checkedfor higher symmetry observed and calculated sffucture-factorshave been with the program MISSYM (Le Pa.ge1987), which submitted to the Depository of Unpublished Dat4 indicatedapossible 2-fold axis of symmety asin space CISTT,National ResearchCouncil of Canada"Ottawa, group P3221.This pseudosymmetrycan be seen in Ontario,Canada KIA 0S2.

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TABLE 3. SHEUTRICKITE: ATOMIC COoRDINATES' rAsLE 4. SSBLDRICICTT! INTERATOIUIC DISTAIICF.5 (A) AND ANGLES e) rsorRoplc DIspL\cEMENTFAcroRs to-) tA'x Napolyh€dm Calpotyhedmn Ci2polyhedrc! Co3Fotthede! AftD BOND YALENCE SUMS (w) Na-FJ 223(l) Csl-Fl 22j

. constanb from Brese ad O'Keffe (1991)

DrscruvnonAND DrscussroN similar polyhedron, with nine-fold coordination.The OFTI{E STRUCTIJRE polyhedron fits within an irregular trigonal prism (Fig. 3b), with the tbreeF atomsdefining the equatorial planeand the othersix ligands,the upperand lower face The structure of sheldrickite has four large-cation of the prism. sites,but only two distinct types of polyhedra-The Na polyhedron,n'ith 8-fold coordinatio4 flts a comprcssed The crystal structure of sheldrickite is layered on octahedron modified by the removal of one edge (001) (Fig. 2). The layering of the REE carbonates (Fig. 3a).The compressedaxis correspondsto the Na-F was described in detail by Grice et al. (L994). In bonds, whereasthe removed edge results in the four sheldrickite,there are two layers of different composi- longer bondswithin the polyhedronClable 4). Each of tion: (1) Na(COr)z'HzO,and (2) CaF. In Figure 2, the tlree Ca siles has a similar stereochemistyand a the pseudo-n planes are positioned through the

Flc. 3. The large-cationpolyhedra in sheldrickite:a) (Na-

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{.* { @@ /-'1 \,-/ "{ ( T JO ) ) I *'o A ,vft 63 @ \J ffiw I I ow l-\ I .a--Y EJ I @

FIc. 4. The structureof bastniisite-(Ce)projected along [00]. .& Dark triangles represent (CO) polyhedra, large light- @@ shadedcircles, F atoms,and smaller dark-shadedcircles. Ce atorns. Frc. 6. The stucture of rouvilleite projeciedalong [@1]. Dark trianglesrepresent (COr) polyhedra,large light-shadedcir- cles, F atoms, sm:ll fgfof-5foa(fficircles, Na aloms, and small dark-shadedcircles. Ca atoms. Na(CO3)2.H2Olayers, and the pseudo-2-foldaxis along [100] is at 0,0,0. The carbonatelayer is of the "mixed- layef' fype (Gice et al. 1994),wherein the oostanding- on-end" (CO3)groups (Gice et aI. 1994) arenot in a "standing-on-end"(CO3) layer. Similar syntacticinter- separatelayer but occurwith the cationsand H2O groups. growthsoccur in the Ba fluorocarbonatescebaite-(Ce), In general, the REE-fluorocarbonateminerals are huanghoite-(Ce) and kukharenkoite-(Ce). Figure 5 layerd have"standing-on-end" (CO) groups, andare of shows tle structure of cebaite-(Ce)(Yang 1995), two distinct types. The membersof the bastnlsite - with mixed layers of "standing-on-end"(CO3) sharing parisite - riintgenile - synchysitegoup are syntactic the slab with the larger B4 Ce and F atoms. The iniergrowthsof various stackingcombinations of REE, sheldrickite structure is a combination of these two F, alkalineearths and (CQ) groups.The bastriisite-(Ce) exftemes,the bastniisite-(Ce)stucture with segregated sffucture(Fig. 4) et al. 1993)is an exampleof rhis Q{i large-cationlayers and (CO3)layers, and the cebaite- group, with two types of layer, a CeF layer and a (Ce) sfructure with integratedlarge-cation and (CO3) groupsin the sarnelayer. Thus, sheldrickitehas a seg- regatedlmge-cation layer andan integratedlarge cation - GIrO)- (Cq) hyer.Interestingly,the strucfire ofrouvil- leite (Yamnovaet al. 1991),which is similar in compo- sition to sheldrickite,does not havethe distinct layering T that other fluorocarbonatesexhibit; it has layering on b (210), with alternatinglayers of Na{a-(CO3) groups I and a Ca-Na--Flayer @ig. 6) comparablein type and compositionto sheldrickite,but not aswell layered.

PARAGENESISop Srmlonrcrrrs

Sheldrickite occurs in a marble xenolith in the nephelinesyenite intusive unit. Although no work has beendone to FIc. 5. The structureof cebaite-(Ce)projected along [001]. assessthe origins of this or other marble Dark triangles represent (CO) polyhedra, large dark- xenoliths in the quarry, it seemslikely t.harthey were shadedcircles, Ba aloms, large light-shadedcircles, F blocks of Paleozoiclimestone caught up in the rising atomsand smallerdark-shaded circles, Ce atoms. silica-undersaturatedsyenitic magrna. The limestone

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was a rich source of Na" CaCOr and F, the F being HoRvArH,L. & GAttLr, R.A. (1990):The mineralogyof Mont evident in such minerals as carletonite, fluorapatite, Saint-I{ilaire, Qtetrlc. Mincral. Rec. 21, 2W360. fluorapophyllite, fluorite, leucophanite,polylithionite, (198?: taeniolite and zeophyllite (Horv6th & Gault 1990).All Lr Pacr, Y. Computer derivation of the symmetry elementsimplied in a structrredescription. J. fupL Crystal- of theseminerals result from hydrothermalreworking 1o9r.20,2tu269. of the Ordovician limestoneinto which the nepheline syeniteof Mont Saint-Hilairewas emplaced. MANDARn{o,J.A. (1981): The Gladstone-Dalerelationship. IV. The compatibility concept and its application. Can ACI(]\IOWLEDGB\,EITs Mineral.19,441450.

The authors tha* Elizabeth Moffatt and Gregory McDowap, A.M., Guo, G.Y. & RAI\4rK,R.A. (1991):Rou- Young, Canadian Conservation Institute, Ottaw4 for villeite. anew sodiumcalciumfluorcarbonate mineral from Mont Saint-Ililaire, Can Mfupral. D, Lm-lll. the infrared and thermogravimetric analyses; and Quebec. Dr. F.C. Hawthorne, University of Manitoba" for use of Nt YUNxANG,HucHEs, J.M. & MaruaNo,A.N. (1993): The the fully automated four-sircle diffractometer. The atomic arrangementof bastniisite-(Ce),Ce(CO:)F, and manuscript was improved by the comments and sugges- structural elements of synchysite-(Ce),ritntgenite-(Ce), tions of two referees, Drs. Andrew M. McDonald andparisite-(Ce). Am- Mineral. 78, 4L5418. and Frank C. Hawthorne and Associate Editor Andrew C. Roberts. Snsonrcr, G.M. (199,0):SHEIX|I. a CrystallographicCom- puting Paclwge (revision 4.1). SiemensAnalytical X-Ray RBFERENcES InstrumentsInc,. Madison Wisconsin. N.A., Pusucrenovsxu,D.Y., KHoMYAKov,A,P. & BRFSE,N.E. & O'Kmre M. (1991):Bond-valencepararneten Yannrova, YvArm{, S,V. (1991):Crystal stucture of the new natural for solids.Acta Crystallagr.B,47, ly2-L97 . fluorocarbonateNa3Ca(MqCaXCO3)3F. Sov. Plrys.Crysnl- Iogr.36,lLl6. Csao, G.Y., CoxuN, R.P. & VeN Valrruml, J. (1990): Mont Saint-Ililaire unknoms. Mineral, Rec.21.363-368. YANG,Z. (195): Structuredet€rmination of natural cebaite- (Ce), BagCq(COt)5". News Jahrb. Mineral, Monatsh., Gnrcs, J.D. (1996): The crystal structue of shomiokite-(Y). 56-9. Can Mineral.A,@9-656.

- VANVnrrrumrr, J. & Gewr, R.A. (194): Peter- senite-(Ce),a new mineralfrom Mont Saint-Hilaire,and ils Received.September 18, 1996, revised maru'tscriptaccepted structnal relationshipto other REE cabonates.Can Min- December13, 1996, eral32, aA54I4.

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