843
TheC anad.ian M ine rala gi st Vol.32, pp. 843-854 (1994)
ABENAKIITE.(CE),A NEW SILICOPHOSPHATE CARBONATE MINERAL FROMMONT SAINT.HILAIRE, OUEBEG: DESCRIPTIONAND STRUCTUREDETERMINATION
ANDREWM. McDONALD* eNpGEORGEY. CHAO Onawa-larlennGeoscience Centre, Departmmt of EanhSciences, Carleton University, Ottawa, Ontario KIS 586
JOELD. GRICE MineralSciences Sectioa Earth Scientes Division, Catnd.ion Mweum of Naare,Ottawa" Ontaria KIP 6P4
ABSTRACT
Abenakiite-(Ce)is a new mineral speciesdiscovered at the PoudretteQuarry, Mont Saint-Hilaire, Quebec.It occursas a single 2 x I mm pale brown ellipsoidal grain in associationwith aegirine,eudialyte, mangan-neptunite, polylithio:nite, seran- ditJ, and steenstmpine-(Ce).IhJstreak ii white, and the luster, vitreous.The mineral is brittle, with a conchoidalfracture and has a Mohs a poor {0001} cleavage.It displaysno discemiblefluorescence under long- or short-waveultraviolet radiation, naiOnesigreafur ttran?, anOei*riUlts a very weak effervescencein l:t ffCL D(meas.)is 3'21, D(calc') 3.27 glcn3 for the empirical-formula.Abenakiite-(C6) is uniaxiat negative,ro 1.589(1)and e 1.586(1).The averageof four electron-microprobe *ilyr"r is Na2o 25.32,Ce2915.31,ta2o3 5.94,Nd2O3 7.78,Pr2o32.02,5n2or0.74,T\o21.42, Sro,0.12, sio2 13.30, P2O; 14.11,-SC,22.28,-iO2 8.90 (calc.)' totil'97.24 wt,Eo' coffespondingto Nlrr.rr(_c:1zf9r,Ll,lr,o-! pri.riTh.,us*o.,3Sri.e3)y5.eSi6.56Fr.*cus,.*ou,on the basisof o = 63 or, ideally,.Na26REEu(Sior)oGo+)o(Co3)6(S#oro wittrz:5. rtli-rtroni6iiiecri,"nS, *in',i-te"oft(2), c 19.761(gA, v 4390.9(l; A3. the strongesteight reflectionsin the X-ray powderpatrern [d in A(O(hft4]are 11.414(?5)(10l),8.036(85X012), 6.554(85X021),4.646Q5)(r04), 3.773(90X131), f.SSitiOlt:fZl, 3.150(i0xt25), 2.674(100)(036).The namehonon the AbenakiIndian Tribe, which inhabited the areaaround Uont'S6nt-Uitaire. The crystal structurehas beenrefined to R = 3.lfto, wR = 3.0V0for 2176 observedtF>6o(Dl reflections. The structure,when viewed along c, may be best describedin terms of a {63} hexagonalnet, with chainsof NaOTpolyhedra joined to POagroups at the nodesof the net and columnsof six-memberedSiOa, NaO7, and NaOT-REEO6polyhedral rings in the center.Within the columnsare NaO6 octahedr4 CO3 groups, and disorderedSO, groups.
Keywords:abenakiite-(Ce), new mineral species,silicophosphate carbonate, X-ray data,chemical composition, crystal structure,Mont Saint-Hilaire,Quebec.
SoM:r,tene
L'ab6nakilte-(Ce), nouvelle es$ce min6rale, provient de L canibre Poudrette,au mont Saint-Hilaire, Qu6bec.Elle se pr6senteen cristaux uniquesellipsoidaux, brun pile, mesurant2 x I mm, en associationavec aegyrine,eudialyte' mangan- d'un min6ral neptunite,polylithionite, -une seranditeet steenstrupine-(Ce).Sa rayure est blanche, et son 6clat, vitreux. Il s'agit cassantayant surfaceconcho'idale et montrantun clivage {0001} d€ pidtre qualit6. L'ab€nakiite-(Ce)ne monfe aucune fluorescenceen lumibre ultra-violette(ondes longues ou courtes);sa duretd(6chelle de Mohs) est inf6rieure I 4, et en pr6sence de HCI (l:l), elle produit une trbs faible efferveicence.La de;itd mesur6eest 6gale d3.2I, et la densit6calcul6e, 3.27 glcrfr pour la fofmule empitiq*. Elle est uniaxe n6gative,o 1.589(1),e 1.536(1).Quatre ardyses d la microsondedlectonique ont ionn6, en moy"*", NirOx.lZ,Cgo, 15.3i, l.a2q5.94, NEo3 7.?8,F'2o3202, Smzo30.74, T1lo2l.42, Sro 0.12,sio2 13.30,p2O5'14.ll,Sb2 2.28, C62-8.90(cali.)-, pour un total de 97.247o(poids), ce qui correspond.i Na24.23 (Cq.7Ndi3;a1.ssPr0j6Ttb6Smo.,rSr6pg.eSi6.56P5.eoa6sr.06o63sur une basede 63 atomesd'oxygbne ou, plus simplement, Na*fn.fSib"l.fpO"j"iCfj"j"tseO,lCi,- f="1 iih,"f.i.r6.'iii.i). C'"rt un min6ral rhombo6drique,R3, avec a 16.018(2), c ti.lOi@) A, V +lSO".SttiA3.t e. nuit ruiesles plusintenses du trac6de diffractionX [m6thodedes poudres, d n \(D(hkl)l sonf 11.4i4(?5X101),8.036(Ss)(012),6.554(8t(021),4.646Qs)(rM),3173(90)(13r),3.s91(80x312),3.1s0(70x12s)' 2.6?4(100X0,O. l, oo- honore la tribu des Ab6nakis, qui peuplait autrefois la r6gion du mont Saint-Hilaire. Nous avons r6solu la structurecristalline iusqu'd un r6sidu R de 3.lVo (wR 3.07o)en utilisant 2116 r6flexions observees[F > 6o(D]. La structue, le long de c, d6crit un r3seauhexagonal { 63}, avecdes chalnes de polybdresNaOT li6s h desgroupes POa aux noeuds du €seau, et au"" d"s colonnesd'anneaux h six membres(SiOa, NaO7, NaO?-IRO) dans le centre. Dans ces colonnesse fouvent desoctabdres Nao6, desgroupes COr, et desgrouPes SO2 ddsordonn6s.
Mots-cbs: abenakilte-(Ce),nouvelle espbcemin€rale, silicophosphatecarbonate, donn6es de diffraction X, composition chimique,sfucture cristalline,mont Saint-Flilaire,Qudbec'
* Presentaddress: Deparment of Geology,Laurentian University, Sudbury'Ontario P3E 2C6' 844 TIIE CANADIAN MINERAI{EIST
INTRoDUcnoN TABLB 1. TSE CIfihitrCAL COMFOSUION (WT.yo) OF ABENAKITE-(Cs) -----F-----7- A single crystal of an unknown phase(IK85) was - discoveredin a xenolith of sodalitesvenite in nephelinesyenite at the Poudrette Nqo 25.U 25.33 25.52 25.37 2532 27.67 Quarry,Mont Saint- cqo. 15.50 15.36 rlu 15.15 1531 16.91 Hilaire, Rouville County,Qu6bec. This phasehas been tero. 6.08 5.86 6.11 5.69 5.94 5.60 recognizedas the new mineral speciesabenakiite- Nqo, 8.04 8.07 7.59 7.41 7.74 11.56 (Ce), named after the Abenaki Pr.q 1.91 2.43 1.95 t.77 2.02 Indian tribe, which sno, 0.88 0.78 0.59 0.70 0.74 inhabitedthe areaaround Mont Saint-Hilaire.Both the Tho, 1.86 r.27 t.zt r.32 r.42 mineml and its namehave beenapproved by the IMA Sro o.12 0.13 0.09 0.13 0.t2 Commissionon New siq 13.71 13.35 13.00 13.14 13.30 t2.39 Minerals and Mineral Names. P"o, r4.60 r4.09 13.70 14.05 t4.Lt t4.62 The type specimenhas been deposited at the Canadian so, 2.34 2.34 2.18 2.28 228 220 Museumof Nature,Ottaw4 Onhrio (#31501). co; (e.10) (8.e5) (8.?O (8.82) (8.9r) 9.05 99.18 97.96 95.94 95.83 e7.24 lo0 OccunnsNcEAND Assocterm Mnm,nars
Avcago of aalysc 1-4 6 mo grain" Abenakiile-(Ce)occurs embedded in sodaliteand is b Calculaed fo lhe fomula, coatedby an unidentifiedrhaMophane-group mineral, which may be a product of its alteration.It is closely associatedwith aegirine,eudialyte, mang4n-neptunite, polylithionite, serandite,and steenstrupine-(Ce).In addition, more tian 72 minerals have been recorded Gasparrini1969). Also soughtbut not detectedwere F, from the samexenolith (Chao et al.l99l). Abenakiite- B4 Ti, Fe, M\, Zx, Y, and Ca. A qualitative energy- (Ce) is a late-stagephase, possibly arising from a dispersionscan indicaled less than 0.2 vrt,VoA12O3. metasomaticevent associated with emplacementof the Resultsof theseanalyses are presentedin Table 1. nephelinesyenite. Deficiencies of 10-13 wt.Voare evident; these are attributedto the presenceof elementswith an atomic Ptrysrcer aNo Optrcar h.opsRrrrs number less than eight or to water, which are not detectableby the electron microprobe. The missing Abenakiite-(Ce)occurs as a single, ellipsoidal constituentwas subsequentlyidentified by crystal- crystal measuringapproximately 2 x I mm. It is pre- structureanalysis to be C in the form of a carbonate dominantly pale brown, transparent,has a vitreous group, on the basis ofits electrondensity, its nigonal lusteroa white streak, and does not fluoresce under planar coordinationby oxygen, its mean cation-to- either long- or short-waveulhaviolet radiation. The oxygenbond distances(1.302 A), and its calculated Mohs hardnessis greater than 4. The mineral is bond-valencesum (3.826v.a.). Bond-valence calcula- brittle with a conchoidal fracture and a poor {0001} tions were alsoused to veri$ the absenceof water and 9lgavage.Abenakiite-(Ce) effervesces very weakly in to detenninethe 4+ valenceof the S in the mineral. 1:1 HCl. The measureddensity of abenakiite-(Ce)is The Na2O concentrationsgiven in Table I are 3.21(2) g/cm3, as determinedby flotation in a heavy systematically low, owing to volatilization of Na liquid and a pycnometer.This agreeswell with under the elecfron beam and possibly to vacanciesin the calculateddensity of 3.27 g/cm3,based on the someNa sites of the structure.The averagecomposi- empirical chemical formula and the cell dimensions tion from Table 1 gives the empirical formula (based refined from the powder data. Optically, abenakiite- on O = 63 from results of the crystal-structureanaly- (Ce) is uniaxial(-), with o 1.589(1)and e 1.586(l) sis): Nara.2r(Cer.rrNd,.rrLa1.s3Prr.r.Thr.rosmo.rs (1,= 589nm). It is not pleochroic. Sro.or5.sgSl6.r6P5.esC6Sr.s6O6, which is closeto the structural formula Na26fiEE6(SiO3)6@Or6(COr6 CrnmcarDare (SO)O, wrthZ=3. Gladstone-Daleconstants (Mandarino 1981) were Electron-microprobeanalyses were done on a usedto calculalea compatibility index of 0.017, indi- CambridgeMicroscan MK5 instrumentusing an oper- cating superioragrcement among optical, physical and ating voltage of 15 kV and an estimatedbeam-current chemicaldata. of 30 nA. The electronbeam was rasteredover atr area of 60 x 60 pm2 to mini6l2e damage1o jtre sample. X-Ray Cnysrar.t,ocnapnyaND Wavelength-dispersiondata were collected using-the Cnysrar,-Srnucnins Dr.rsRlvm{ATIoN following standards:albite (Na), hornblende (Si;, apatite @), celestine(S, Sr), REE glasses(Ia" Ce, h, Precessioncamera photographs show abenakiite- Nd, Sm), and ThOr. Thesewere reducedusing a (Ce) to be_rhombohedral,with possible space-groups modified version of EMPADR VII (Rucklidge & R3 and R3. The observedX-ray powdeipattern for ABENAKtrTE-(Ce) FRoM MONT S{NT-HILAIRE 845
TABII 2. X-RAY.DIFFRACTION DATA FOR abenakiite-(Ce)(Table 2) was obtained u$ing a ABENAKIITE-(Co) 114.6-mm Gandolfi cameraand Ni-filtered CuKa d* td de I@ radiation (1, = 1.5418 A;. It agreeswell with that calculated from the crystal structure using the (Sheldrick ll.4l4 75 t1353E 53 101 SIIELXTL PC packageofprograms 1990). 8.036 85 8.0478 6l 012 The rmit-cell parameters,a 16.018(2),c 19,761(4)A, 6.5870 25 003 A3 and Z = 3, were refined from the 6.554 85 6.5446 55 ozt wrth V 4390.9(1) 5.696 l0 5.6769 9 202 powder data using the program CELREF (Appleman 5.066 60 5.0678 31 tzl & Evans 1973).Indexing was carried out using the 4.U6 4.6539 27 104 4.63t4 5 t22 intensitiesofreflections on tle precessionphotographs 4.624 13 030 as a guide. 3,94 I 4.@45 l0 220 data were collected on an 3.7n 90 3.78/6 48 303 X-ray intensity 3.7165 47 l3t Enraf-Nonius CAD-4 diffractometer using a disc- 3.591 80 3.5956 26 shapedfragment of dimensions0.27 x 0.36 x 3.5852 29 3.420 3 3.4218 6 a1a 0.09 mm. which was mountedto rotate about c. The 3.150 70 3.1560 52 grain was found to be optically homogeneous,with a 3.024 50 3.0292 l0 232 polars. 3.d271 10 410 sharp, uniforrn extinction under crossed Data 2.U4 5 2.&t84 6 404 measurementand reduction (Lorentz, polarization, 2.745 20 2.7568 7 31' were done using the NRCVAX 2.7506 12 143 backgtound,scaling) 2.674 100 2.682,6 100 036 packageof computerprograms (Gabe et al' 1989).No 2.6697 89 330 absorptioncorrection was applied becauseof the low 2.@4 10 2.6067 8 045 2.5988 4 241 linear absorptioncoefficient ttrr{MoKo) = 4.91 cm-rl 2.532 l5 2.5355 9 and the small size of the crystal used. A set of 2.856 5 t1a permuted 2.471 45 2.4742 11 333 42 ref'lecliors (L5"<20<27o) four ways 2.47t9 t4 5ll @h at t20) was used to refine the cell dimensions, 2.414 2.4159 5 152 a 16.02O(2),c 19,92O(4)A, andV 4427.4(l) A3, which. 2.3t2 I 2.3t57 7 244 'l 2.272 tl 2.2760 t37 are in good agreementwith those refined from the 2.270a I powder data. A full sphereof X-ray intensity data to 2.2346 5 t2a 2.222 2.U87 5 L46 20 = 55" was collected.Further information regarding 22213 t2 520 datacollection is presentedin Table 3. 2.t957 l0 009 of abenakiite-(Ce)was solved 2.181 50 2.tu6 8 425 The crystal sffuctue 2.1815 3l 063 using direct methods and refined in the spacegroup 2.t02 40 2.1048 9 58 R3 using the SHELXTL PC packageof programs 2.1034 7 l6t 2.0786 7 318 (Sheldrick 1990). Scatteringcurves for neufral atoms 2.0706 5 474 . and anomalousdispersion corrections were takenfrom t.976 1.9834 9 039 Cromer & Mann (1968) and Cromer & Liberman t943 10 t.9473 6 t@ t.9430 5 nat (1970),respectively. From the E-map,the positionsof t.9L7 l0 r.9210 5 247 the rare-earthelement (assumed to be entirely Ce), Si, l.9tJ7 2 621 1.890 45 LA9Z3 4 066 P, two distinct Na atoms,and an O atom were identi- 1.865 1.8680 6 517 fied. Difference-Fouriermaps of this initial model 1.8651 15 615 l.&t8 5 LCA74 2 710 1.802 l5 1.7816 1l 01.1I 1.7698 l0 173 \7574 5 13.10 1.7541 1 158 TABLE 3. !6CEI.I.ANEOIIII DATA RORDT'IERMINATION OT IIIE CRYSTAT 1.7040 7 339 STRUCTURE OF ABENAKtrI!-(Co) 1.688 25 1.6893 7 353 1.6885 7 sp@Golp R5(c418) Diffta6a6 Edd-NciB cAD4 1.670 t5 t.67t4 6 544 a 1A) 160'g.2r Rsdidi@ MoKo (50 w, ?, EA) 1.6703 3 722 1992&.4Y !vl@[email protected] Gi4t!i!e 1.61E 10 1.6200 9 45J z'tA) un.qL') Ctysial $qe Bla, oodin 1.5096 10 5.10 z Crydal St6 027x036x0.09 m 431ffr 1.604 1.6046 3 /to Forofa) 1.5644 7 23.11 (h€d€lF@lB N%RrBd{sioJ6tPoJ6(co,Xso;P t.5513 t2 03.12 InJ@ity h Cotrdi@ e2@8@hgodo t.542 1.5438 19 366 20 Usit 55c Iatority Shd6ds TtF @qy ro,0@ '@d8 pluo6w oliffi@StedEls Itr@ {e6y 4{X) rdeti@ No. of Uaiqo Re0e TABLE 4. POSfiONAL AND THERMAL PARAMETERSFOR ABENAKIITE-(Co) Utt u, U,, U"" U,, UD uq si 0.4299(r) 0.8652(l) 0.1271(r) 85(6) e5(6) 116(6) 7(5) 4(5) 48(5) e8(5) P 0.3185(l) 0.000q1) 0.0009(1) 144(6) 140(6) 201(6) e(5) 12(5) 7e(6) 158(5) Na(l) 0.348(2) 0.3483(2) 0.1714D 2e8(r3) 47s(16) 23r(t2) -30(lr) -2(10) 310(13) 283(11) Na(2) 0.s52s(2) 0.1046(2) 0.7103(1) 182(12) 255(13) 330(13) -8e(lo) 58(lo) 2(10) 303(lo) Na(3) 1B 2/3 0.0230(2) r24(rr) 124(t1) 3342r) o o 62(6' 193(lo) N(4) 0.2088(2) 0.785q2) 0.737E2) 483(18) 26(14) 4e8(18) 104(13) -151(14) 6413) 468(13) Na(5) 0.1121(2) 0.208e(3) 0.w75(2) 350(16) 76e(23) 46Er7) 43E17) 23r(r3) 40e(16) 472(15) REE 0.53552(2) 0.l 1288(2) 0.05834(l) I l(l) 7q1) t25(l) 60) le(l) 48(l) 106(l) c 0.26s7(3) 0.7643(3) 0.8747(2) l10(21) e4(20) 82(le) 16(16) -2e(r6) -e2{r7) 15e(16) s28 1B rB 585(14) o(1) 0.4400(3) 0.8250(3) 0.0555(2) 184(19) 155(18) 125(17) -6(14) 14(14) 86(16) 15(15) q2) 0.314t(3) 0.8141(3) 0.1462(2) 106(17) 263(21) 165(18) 4q.lq l(r4) 5e(17) le3(15) o(3) 0.8317(3) 0.lel4(3) 0.8014{2) 237(20') 24eQ1) 175(18) -22(1s) -17(15) 182{18) le4(16) o(4) 0.5001(4) 0.8052(4) 0.8433(2) 604(33) 336(27) 24r(22) re(le) 33(21) 3nQq 355(23) o(5) 0.3e40(3) 0.e682(3) 0.ee47(2) 24q2r) 217(22) 27421) 49(17) -16{17) lee(le) 235(18) 0(6) 0.6046(3) 0.e600(4) 0.734qD 25E24) N6(27) 256(23) 22(20) 8(18) 85(21) 342(20) o(7) 0.6301(3) 0.9079(3) 0.es5{2) 1e?(21) ?3fi(n) uo(26) -105(le) -30(le) 120{1e) 285(18) o(8) 0.76e1(3) 0.073l(3) 0.e6t7(2) 268(U) 260(24) 443(27) 9l(20) t2e(2r) eE20) 33e(20) o(9) 0.3277(?) 0.u27(3) 0.8480(2) 307(24) 197(21) 3a0{.?3) 86(18) z(re) 45(le) 30(18) o(r0) 0.46r8(3) 0.7r62(3) 09317(2) 230(21) 151(18) 232(20) 12(ls) e8(16) 72(17) 214(1.6) o(11) 0.s774(14) 0.2456(15) 0.3374(r0) 588(48) Note: Anisotro,picternpercuro factors have the form exp l-2t 1t?aatlr, + Fbnuo ... + 2hharb'Ue)l: all U values ro in A x 10a; estimatedst@drd aleviaioasin pareutl€ses. ABENAKIITE{Ce) FROM MONT SAINT-HILAIRE 847 TABLE 5. SEX.ECTTDTNTRAmMIC DISTAI{CES 6) AND BOITTDANGLBS f) FOR ABB{AXII1E-(Og) Sio. tsnahedrcn N{ )O' polybedm si o(3) 1.606(5) o(3) -si -o(t) \7.6(2' o(3) 40) 2.74(8) Na(4)-o(4 2.395(6) o(7) -N(4!o(6) 12r.0(3) q, q6) 4.264(r) -o0) r.50(4) -o(2) r07.4(3) -o(2) 2.628(8) -o(4) 2.4n(q {(8) 83.0(2) -c{E) 3.339(8) -q2)" 1.65s(4) .O(2)* r05.8(2) -o(2r4 2.607(8t -0(6) 2.509(J) 4(11)' 107.4(4) -o(11). 4.070(8) -o(2)f t@{5) o(l) -si o(2) 108.5(2) o0) -o(2) 2.648(8) -o(3) 2.634(0 -o{11) 128.0(5) -o(11) 4.566{8) N{5)O, polyhedor N{l)O? polyhedm Ns(5!o(8) 2149(7) o(8) -Ns(5)4(O e3.E2) q8) -q6) 3.313(8) Na(1)-o(6) 2.342(5) qq -N(l!o(e) 126.r(2, qq 4(e) 3.604(8) -0(6) 2.2e0(r) -o(e) e3.4(3) qe) 3.365(8) -o(e) 2.407(2' .q3)' 82.2(2) -o(3)' 3.263(8) -a{q n47a -o(lr). 78.9(3) -qll)r 3.10e(8) -o(3r 2.6n(6) -o(2) 103.(2) -o(2) 3.yi2(8) -o{e') xn6) -o(u) %.3(6) -qll) 3.6ee(8) 4Q' 2.u6) 8(7) 125.t(2) -o(a 4.571(8) -o0\a 2.642) -o(3) 8r.9(2) -o(3) 3.594(8) -c(8) 2.?6(5) -o(3) 100.e(2) -o(3) 3.e56{8) -o(rrt 2.70(2') qo -N{J)q4) 83.6(3) qo -o(4) 3.08e(8) 4A 2.nq5' qe) -Na(t)-c{z) r%2Q) qe) -o(2) 4.573(8) -o(3) 2t4Z(5) -o(9) 147.4(2' -o(e) 4.47q8) 4(t) ZJZQ' .o(E) 81.0(2) -o(8) 3.366(8) N(2)O? polyhedru c o(e) r.265(6\ o(e) { q4) ra.1(J) o(e) -o(4) 2J6(E) o(4) 1.28q6) -o(ro) 117.4(4) o(10) 2.23E8) -N{2}O(2) N{2}o(8) 2.25r(4) o(8) e5.3(2) o(8) .(){2) 3.62(8) -o00) t3t:(o o(4){ -qro) u69(4) q4) qlo) 2212(8) -oo) 23eqs) q7) 8e.4(2) -qD 3.33e(E) Na(3}o{r) 2.331(4)e3 o(l) -Na(3}oof ll2.(Ur3 O0) -O(l)i 3.879(8) -oO0) 2j3(5) x3 -q10) 78.6(llx3 -oO0) 1.046(8) NolrN E$haed seddddcyldm8 hf€dose& $nnbols:' deoes Btrl@ral€d am. +d!iloEsddgfugorlaa rM. The other major polyhedralunits in the structureare tube unit (Frg. 3) consistsof tbree different types of the complex colurnns that occupy the centersof the six-memberedrings: (i) a Na-O polyhedralring, com- hexagonsoutlined by the polyhedralchains (Frg. 1). posedof edge-sharingNa(4)O7 and Na(5)O7poly- These complex columns may most clearly be hedra, (ii) a Na-REE-O polyhedral ring, composed describedin terms of two subunits:(1) a hollow tube of edge-sharingNa(2)O7 and REEOepolyhedr4 and unit, and (2) the channel occupantunit. The hollow (iii) a silicate ring, composedof comer-sharingSiOo 848 TTIE CANADIAN MINERALOGIST TABLE6. EMPIRICALBOND VAIJNCES (t.e) FORABENAKUII-(Co) N4r) N42) N{3) Nd4) N{5) REB q1) 0.200 o.238tx3) 0.4t2 l.u'l t.957 o(2) 0.08:1 0.175 0.r20 2.076 0.898 q3) 0.071 0.059 0.517 1.050 0.112 c(4) 0.152 0.228 0.318 o(5) 0.032 0.576 2.076 0.242 q6) 0.231 0.056 0.147 1.303 z.oo3 q7) 0.073 0.155 0.200 0.371 t.173 t.912 q8) 0.074 0.296 0.105 0.297 t.3t4 2.086 qe) 0.t94 0.213 0.?34 1.402 2.120 c{10) 0.136 0.162(x3) 0.216 1.099 1.881 0,268 qll) 0.w2 0.088 r.827(x6) 1.957 0.101 0.108 EV 0.fit9 l-050 t.2N 0.7471 1.128' 3234 3.915 4.y16 3.826 3.654r t Note: Bqd-val@@ msrmts ued in the @l@ldi@ ae &om Brs md oKe€fie (l9l); @lqul6ed sitrg the roffn€d O(ll) site o@{rpeqy of ll3. teuahedrathat are arrangedin a IUDUDUD) manner to form a Si6O18ring. The three types of six- memberedrings are joined along c through shared edgesand corners,thus forming hollow tubes.The channel occupantunit (Fig. 4) consistsof three different types of polyhedrathat occupy the channels within the hollow tubes.These polyhedra include (i) a disorderedSO2 group, (ii) carbonategroups, and (iii) NaO6octahedra. The disorderedSO2 group lies along the 3 axis and is positionedin the centerof the Na polyhedralring of the hollow tubes. The S atom is bonded only to the O(11) atoms,which lie on a six-fold equipoint.As the site-occupancyfactor for O(11)refined ta 34Q)Vo, it would seemthat only two O(11) atoms are bonded to S (/a x 6 = 2). Bond-valencesums, calculated from the observedS-O bond distancesand the constantsof Brese& O'Keeffe(1991), are3.654 v.z. assumingS4 and 3.462 v.u. assumingSc. Therefore, S4 is inter- preted to form a SO2group with O(11). Further evidenceto supportthe presenceof SO2comes from (l) the averageO-S-O angle in abenakiite-(Ce), which is 1I9.7(l)", very closeto the valueof LL9(2)' given for crystalsof SO, @ostet al. 1952),and (2) the iverage S-o bond in ibenakiite-(Ce),^1.422Q) A, W closeto the valueobserved in SO2,1.43 A @ostet al. 1952).Analysis of the environmentaround S on dif- Complex columnsl Polyhedral chains ference-Fouriermaps failed to revealany indication of group Fro. 1. The {63} hexagonalnet in abenakiite-(Ce)projected additional O atomsbeing bondedto S. The SO2 down c. is thus disorderedover six orientations (Fig. 5), the ABENAKtrTE-(Ce) FROM MONT SAINT-HIIAIRE 849 Frc. 2. The_polyhedralchains in abenakiite-(Ce)projected down[110]. e disordering being reflected in the large isotropic displacement-factorsof S and O(11) and the fact that c neitherof theseatoms could be refined anisotropically. Since O(11) is also bondedto Na(4) and Na(5), the S02 group probably is essentialto the structure. Whereasthe presenceof an SO2group in abenakiite- (Ce) may be controversial,sulfur dioxide is an accepted ligand in certain synthetic compounds(Ryan et al. 1981,Cotton & Wilkinson 1988).One such compound is tMg(So)(AsF)2lo whosestructure has been solved by Hoppenheitet al. (L982). They observedthat octa- hedrally coordinated Mg2+ cations had two trans Mg-G-S-O linkages with S-O bond distancesin the raige of 1.37704tb l.Ml(12) A laverage1.4L2 L) and G-S-O bond anglesfrom 115.3(8)to 116.8(9)". ffim Ftc. 3. The hollow tube componentof the complex colurms in abenakiite-(Ce)projected down Na(1)O" [110]. r"d83a,u Polyhedra I Nd4)O" w Poly,he&b Na polyhedralring Na(5)O" I W Polyhedtb REEO^ Na-REE polyhedral ring W Polyhedla Na(2)O, I T Polyh&lrb Silicatering E-t sio l t::;:=-:lTetrahdra c 850 TIIE CANADIAN MINERALOGIST Ftc. 4. The channeloccupants of the complex columns in abenakiite-(Ce)projected down I l0l. The Na(4,5)O7 and Na-REE-O polyhedral rings have been omitted for claritv. c ffi @ ffi sio4 Na(3)Ou s o(1r) col Tetrahdra Octahedra atoms atoms Groups Such linkages seem to be similar to the M+ 3AsF5+ SO, -+ Na(4,5)-O-S-O linkages in abenakiite-(Ce),and the [M(SO)(AsF6)2J^+ AsF, observedS-O bond distancesand anglesare in good agreementwith those observedin abenakiite-(Ce). (Hoppenheitet al. 1982). Such a reaction is quite Complexesof the type tM(SO/(AsF)zlo(M = Mg, Fe, interesting when one considersthe geochemical Mn, Co, Ni, Zn) have been synthesizedby the oxida- featuresof the environmentin which abenakiite-(Ce) tion of pure metal by AsF, in liquid SO2through the crystallized. These include the presence of reaction: (l) numerousF-bearing species such as villiaumite ABENAKtrTE-(Ce) FROM MONT SAINT-HILAIRE 851 Ftc. 5. One of six possibleorientations of the SO2group (shaded)projected down c (a) and a O). <- (NaF), kogarkoite [Na3(SOa)aFland vuonnemite NqMzft(SizO7)f2'2Na3POal, (2) As-bearingphases such as arsenopyrite(FeAsS) and liillingite (FeAE), and (3) native Sb and Bi (group-VB elements).Thus, many of the chemicalconstituents requhed to synthe- size known SOlbearing compoundsunder laboratory conditions were apparently available in the sodalite syenitexenolith in which abenakiite-(Ce)formed. The secondtype of channel occupantis the carbonate Frc. 6. Plan of the cations in the abenakiite-(Ce)structure from ? = 0 to e = %. Heights in e of atomsin the asym- metric unit are labeled. Circles are envelopesabout the complex columns.P atom$of the polyhedral chains are locatedat the nodesof the {63} net. The unit cell is indi- b cated. I I Na(3) Na(2) Na(5) Na(4) 852 T}IE CANADIAN MINERALOGIST Na(3) Na(2) Na(1) si +.21 Na(5) Na(a) REE Ftc. 7. Plan of the cationsin the abenakiite-(Ce)structure from 4 = tla to 2 = /a. Heights in z of the atomsin the asymmetric unit are labeled.Circles are envelopesabout the complexcolumns. Na(l) atomsof the polyhedralchains are locatedat the nodesofthe {63} net. The unit cell is indicated. group, which lies in the Na-REE-O polyhedral ring of the polyhedral chains are linked to the complex with its planar surfaceoriented approximately parallel columns by sharededges with the Na-fiEE-O poly- to c. This group is located at the periphery of the hedral ring and cornerswith the Na(4,5)O7polyhedral channel,occupying triaugular gaps formed between ring. REEO' and NaOTpolyhedra. The third type of channel The abenakiite-(Ce)structure also has a distinct occupantis Na(3)Ouoctahedron, which is bondedto layered aspectand may be alternatively describedin two different SiuO* rings along c. The Na(3)Ou terns of two different compositelayers along z (pard- octahedronshares oxygen atomswith three SiO, tetra- lel to c). The first layer (Frg. 6) extendsfrom z = 0 to z hedrafrom the silicate ring aboveand with three SiOa = Ve,and the secondfrom 3 = Llato z = % (Fig.7), tetrahedrafrom the silicatering below. The two compositelayers are joined along c through The channeloccupants and the polyhedral rings of sharededges and cornerswith the Na(l)O, polyhedra the hollow tubesare bondedtogether to form complex and POaofthe polyhedral chains.Lateral linkagesare columns that are repeatedlaterally by the 3, and 3, attainedby (1) SiuO,, rings and six-membered axes.The complex columnsare in turn cross-linkedto Na(4,5)O, polyhedralrings sharingedges with the polyhedral chains through fwo types qf linkages; Na(l)O7 polyhedra,and (2) the Na(4,5)O, and (l) the Na(l)O, polyhedraof the polyhedralchains Na-REE-O polyhedral rings sharing edgesand are joined to the complex columns by sharing edges comerswith the POatetrahedra. and faces with the Na(4,5)O, polyhedral ring and The abenakiite-(Ce)structure appears to be unique edgeswith the silicate ring, and (2) the POotetrahedra in its topology. The six-memberedsilicate ring that is ABENAKtrTE-(Ce) FROM MONT SAINT-HII-AIRE 853 linked to a NaO6octahedron is somewhatreminiscent Acro{owr-eDcEhml.lrs of that found in steenstrupine-(Ce),NaroCeuMn3+ Mn2+FgZr(Si6OrJeOrT(OH)2.3H2O (Moore & Shen ![e fl1ankthe following for their cooperationand 1983)andkazakovite, N%Mn{T(Si6O16)} (Voronkov support: J.T. Szymafski of the Cana{a Centre for et aI. 1979), minerals that occur in highly alkaline, Mineral and Energy Technology,Ottawa, for the use SiOr-deficientrocks like that in which abenakiite-(Ce) of and assistancewith the single-crystal diffractom- was discovered.All three minerals contain six-mem- eter, Y. l.e Pageof the National ResearchCouncil of beredsilicaie rings that are arrangedn a {UDUDUD} Canadafor providing computing facilities, P.C. Jones mannerand are comer-linkedto octahedraabove and for the electron-microprobeanalyses, T,S. Ercit for below the plane of ttre ring. In abenakiite-(Ce),the help with the structurerefinement, and J.M. Hughes, silicatering haspoint-group symmeby 3, and the octa- R.C. Rouse,P.B. Moore and R.F. Martin for construc- hedrally coordinated cation is Na. In steenstrupine- tive criticisms and editorial comments.This work was (Ce) and kazakovite, the rings have point-group partially supportedby NSERCoperating gant A5113 symmetry 5m, and the octahedrallycoordinated toGYC. cations are (Zra+,Fe3+, Mn2+) and (Ti4+,Mn2*), respectively.An important difference among these ReFERm{cFs mineralsis the way in which this ring of octahedraand tetrahedramotif is linked in the structure.In both Apptsraer.r,D.E. & EvANs,H.T., JR. (1973): Iob 9214: index- steenstrupine-(Ce)and kazskovite,the central octahe- rlg andleasrs-Quares refinement of powderdiffraction surv', compat'contrib' ?'0(NTIS Doc' dron links adjacent silicate rings together, forming W !:!:^9-L sheetsperpendicular to c. In areiatiitJ-(ce), howevei PBlt6188)' the silicate nngs and NaO6octahedra are isolatedfrom BnrsB,N.E. & .,IGEFFE,M. (1991):Bond_vatence pa*ulxe_ similar units in adjacentcomplex columns. tersfor solids.A cta Crystailogr.Wl, lg1-lg7. Certain Si- and P-bearingminerals like abenakiite- (Ce) contain essentiallywell-ordered Si and P. We Cnao,G.Y., cRrcB, J.D. & cAulr, R.A.(1991): Silinaite, a proposethat they be classified into their own unique new sodiumlithium silicatehydrate mineral from Mont chemical class, the silicophosphates(McDonald Saint-Hilaire,Quebec.CanMineral.29,359-362. 1992).Currently, this group is known to include (1988): twelve minerals,including abinakiite-(Ce). There ar CorroN,F.A. & wILIo'{soN'G. Advancedlrarganic also six additionalminerals that are potentialsilicoi chemistry(frfthed')'Jobnwiley&Sons'NewYork' phosphates,but which require further work to study Cnolurn,_.- D.T. & L*'RMAN,D. (1970):Retativistic calcula_ the degreeof to which Si and P are ordered in their tfi;i;;rb", scatterlngiacton for X '',ys.J. Chen structures(McDonald 1992). Besides the high degree phys.53,1891-1898. of Si-P order, silicophosphatesare characterizedby crystal-chemicalsimilarities that include the absence & MANN,J.B. (1968):X-ray scatteringfactors of a SiOa-POa linkage through a common oxygen, computedfrom numericalHarree-Fock wave functions. unpolymerizedto weakly polymerizedSiOo groups, AcnCrystallogr.AL4,32l-324. unpolymerizedPOa groups, layered structures(most o^"ri# tt*ionlv witrrsio-u *,b 19* srou_ps o"cu.'ing in l.tJAffij,k3$ffiTij Lf*r::'ri.,L"f different layers, separatedby layen of octahedraor of ;;#; i;; #;;; analysis.J. Appr. Crysta,ogr. 22, largercoordinationpolyhedra),highlycoordinated ig+iy. cations and high concentrationsof alkali or alkaline- earthmetals (McDonald 1992). Gnrcn,J.D. & McDoNar,o,A.M. (1993):Silicophosphate Like abenakiite-(Ce),most of the known silico- minerals:crystal chemistry and genetic significance, phosphatesoccur in snongly alkaline,agpaitic rocks Geol.Assoc, Can, - Mineral.Assoc. Can., Program suchas thosefound at Mont Saint-Ililaire, Quebec,the Abstr.18, A37' Khibina and Lovozero massifs of Russia, and the Msws'R' (1982):Metal Illmaussaq intrusion of sourhwesternGreenlanJ w' & complexes'z' Narurforsch' 37b' (McDonald p "oTT:T";P:,1S^"YT" 1992). Thehigh degreeof si and .rd; ill}irlil.tu" is probably due to a combinationof differencesin chargeand ionic radius betweenSi and P, along with MANDApo.{o,J.A. (1981):The Gladstone-Dalerelationship. presenceoflarge cations,which tend to stabilizeweak tV. The compatibilityconcept and its application,Cart Lewis acidssuch as [HSiO4]3-and [HPOr]-2,and H+, MineraLl9,44l450. which acts as network modifiers, suppressingsilicate TheCrysnl Stnrcturesof rhree polymerization(McDonald 1992,G\ce & McDonald M"?-9IT-lll'Y;\Y4t ise:).rh"se controls affecring development orthJ y::;,H:,;Ii;ttrJ;;!f;l;,f!"6:;ff#;l;':f silicophosphatesvrill be the focus of a forthcoming siii"iiniipnrirr. pl.o. thesis, Ortawa-Carteron paper. GeoscienceCentre, Carleton Univ.. Ottawa, Ontario. 854 THE CANADIAN MINERALOGIST Moons, P.B. & Snqv, J. (1983): Crystal strucnre of sreen- Surlonrcr, G.M. (1990): SHELXTL, a Crystallographic strupine: a rod structure of unusual complexity. ComputingPackage (revision 4.1). SiemensAnalytical Tscfurmaks.Mineral Petrogr. Mitt. 31, 47-67 . X-ray Instrurnents,Inc., Madison,Wisconsin. Posr, B., Serwanrz, R.S. & Faurucunr.l,l. (1952):The crys- VonoNrov, A.A., PuDovKrNA,2.V., BLrNov, V.A., tal structure of sulfur dioxide. Acta Crystallogr. 5, ILIUKHIN,V.V. & PyarsNro, Yu.A. (1979): Crystal 372-374. structure of kazakovite, Na6N{n{TdSi6Olsl}. Sov, Phys. Dokl.24.132-134. Rucxrocq J.C. & Gaspenpu.n,E. (1969): Elecnon micro- probe analytical data reduction EMPADR VII. Dep. Geol., Univ. Toronto,Toronto, Ontario. Rver, R.R., KuBAs,G.J., MooDy, D.C. & Er-rsn,P.G. (1981):Structureandbondingof transitionmetal-sulfur ReceivedMay 21, 1993, revised.manuscript accepted dioxide complexes,Stru.cture and Bonding 46,47-rc0. May 20, 1994.