American Mineralogist, Volume 64, pages 563-572, 1979

Agrellite, Na(Ca,RE)rSinOroF:a layer structurewith silicatetubes

SusRerA,GHosu AND CHE'NG WAN Departmentof GeologicalSciences, Uniuersity of Washington Seattle, Washington98 I 95

Abstract

Agrellite, Na(Ca,RE)rSirOr'F,from the regionallymetamorphosed agpaitic peralkaline rocksin villedieuTownship, Qu6bec, is triclinic, Pl, with celldimensions: a : 7.7s9(2),b:18.946(3),c:6.986(1)4,a:89.88(2),0=rt6.6s(2),y:94.32(2)";Z:4. The crystalstructure was determinedby the symbolicaddition method and refinedby the method of leastsquares to an .R factor of 0.045,based on 5343reflections measured on an automaticsingle-crystal diffractometer. The averagestandard deviations in Na-O, Ca-O, and Si-O bond lengthsare 0.004,0.003, and 0.003Arespectively. Due to the presenceof pseudo-C-center,the sodiumpolyhedra and the silicatetetrahedra occur in pairs, whoseconfigurations are nearlyidentical. The crystalstructure of agrellite consistsof two differentNaO, polyhedrawhich are distortedcubes, two eachof CaOuF octahedraand cao.F, polyhedra,and two different lsisoro] doublechains. These double chainsare hollow tubes,formed by the polymerizationof two vlasovite-type[SLo,r] single chains,consisting of corner-sharingfour-membered rings. The silicatetubes, whose diameter is definedby a basket-shapedsix-membered ring, run parallelto the c axisand are hexagonally close-packedin the(001) plane. The sodiumatoms occurring in cavitiescross-link these tubes to form sodium silicatelayers parallelto the (010) plane; theselayers alternate with the calcium polyhedrallayers along the b axis to form a three-dimensionalframework. The averageSi-O bond lengthis l.6194; the non-bridgingSi-O bond lengths(av. 1.5794)are significantlyshorter than the bridging ones(av. 1.632A).The averageNa-o bond length withinthe NaO' polyhedrais2.667A. Withinthe CaOuF octahedra and CaOuF, polyhedra the averageca-o bond lengthsare 2.374 and 2.5954,and the averageCa-F bond lengthsare 2.197and 2.430A,respectively. Along with narsarsukite,fenaksite, litidionite, canasite, and miserite,agrellite belongs to a distinctclass of silicates,whose structures consist of silicate tubes.

Introduction ZrSirOz).Gittins et al. (1976)have determined the Agrellite is a recentlydescribed rock-forming sili- chemicalcomposition and crystallographicand opti- cate with the chemicalcomposition: (Nan.o.Ko.or) cal propertiesof agrellite.For the purposesof the (Car.roREo ,r) (Mn, Fe. Sr, Ba, Mg, Sr)o.rn (Siru..rAlo.or) crystal-structuredetermination, the chemicalcompo- Orr.ro(F,,rOHo.r,).It is found in agpaiticperalka- sition of agrellitehas beensimplified to Na(Ca,.ro, line rocksof the Kipawa Complex,Villedieu Town- REo016)SLO,'F. The crystalstructure of agrellitehas beenbriefly reported by Ghoseand Wan (1978a). ship,T6miscaming County, Qu6bec, Canada (Gittins et al., 1976).It occursas prismaticwhite triclinic crystals(up to l0 crn long) in pegmatiticlenses Crystaldata and gneissescomposed principally of , mi- A smallcleavage fragment of agrellitewas ground crocline, -augite,alkali amphibole, with to a spherewith a diameterof 0.25mm (Bond, l95l), or without eudialyteand nepheline,and sometimes which was mounted on the computer-controlled hiortdahliteand other membersof the wiihlerite single-crystalX-ray diffractometer(Syntex Pl). The group, mosandrite,britholite, miserite,vlasovite, unit-cell dimensionswere determinedby least- calcite,, clinohumite, norbergite, , biot- squaresrefinement of the 20 values(between 30 and ite, phlogopite,galena, and an unnamedmineral (Ca 40o) measuredfrom 15 reflections,using mono- 0003-004x/79/0506-0563$02.00 563 564 GHOSE AND II/AN: AGRELLITE chromaticMoKa radiation(Table l). The dimen- Table l. Agrellite: crystal data sionsof the triclinic unit cell are in good agreement with thosedetermined by Gittins et al. (1976),except Agrelli!e, Na(Cr,R.E. )2S14O1OF that we havechosen the anglea as acuterather than V1l1edieu Tomship, T6miscaming County, Qu6bec, Canada obtuse,to maintaina right-handedaxial system. An colorless transparenE prisms, N.M.N.H. # 134022

1(z) test of the measuredintensities indicated the Triclinic, I centricspace group P7, which was subsequentlycon- o(L), t.tsg(z) Space group: P 7 firmed by the crystal-structuredetermination. b(i.)' ra.s+e(:) cel1 volume 1,i3; r sr+.ztl)

.@y, o.seolr) cel1 contenc: 4[Na(ca,R.E.)2si4o1oF] -? Collectionof the intensitydata o("): s9.88(2) Dt 2.902ecn' -1- The X-ray intensity data were collectedfrom the B("), rro.os(z) Da: 2.887 c cn single-crystalsphere on the SyntexPT diffractometer .((")t s4.34(2) p(Mo,(o): r-8.20 cm-l by the 0-20 method, using MoKa radiation mono- chromatizedby reflectionfrom a graphite "single" crystaland a scintillationcounter. The variable-scan The combinationof 5 symbolsyielded 32 solutions. method was used,the minimum scanrate bein9 2o/ Four E-maps appearedequally probable,out of min (50 kV, l2 mA). All reflectionswithin 20 : 60" whichone showed a geometricallybetter view of the were measured,a total of 5343reflections, out of structure.From this E-map,positions of 4 Ca, 7 Si, I which 1436were below 3o(1),where o(1) is the stan- F, and 14 O atoms were determined.Two cyclesof dard deviationof the intensity1, asdetermined from structure-factorcalculations followed by difference the counting statistics.For all reflectionsless than Fourier synthesesyielded the positions of all the 0.7o(I),the intensitywas set to 0.7o(1),regardless of missingNa, Si, O, and F atoms.A few cyclesof whetherthe measuredintensity was positive or nega- refinementusing the isotropic temperaturefactors tive. The measuredintensities were corrected for reducedthe R factor to 0.086from an initial valueof Lorentz, polarization,and absorptionfactors. 0.40. The isotropictemperature factor for Ca(lA) turned out to be negative,indicating partial occu- Determinationand refinementof the structure pancy of this site by the rare-earthatoms. A differ- The crystal structurehas been determinedby the enceFourier synthesis also indicated positive electron symbolicaddition method (Karle and Karle, 1966), densitiesat the Ca sites.Hence, a site-occupancy using the computer program MurrlN (Germainel refinementof the calciumand rare-earthatoms was al., l97l). 351 reflectionswith E values)1.8 were carried out, using the full-matrix least-squarespro- usedfor the phasedetermination. The phasesof the gram RnrNr (Finger, 1969).The scatteringfactor for following three reflectionswere chosen to definethe the rare-earthatoms was approximated by averaging origin: the scatteringfactors of the rare-earthatoms in the chemicafanalysis reported by Gittins et ql. (1976). hk I E Phaseangle The site-occupancyrefinement indicated most of the l -13 0 2.98 00 rare-earthatoms to be concentratedin the Ca(lA) 4 -19 2 2.88 00 site;the temperaturefactor for Ca(lA) becameposi- 40 -5 2.74 00 tive. The R factor at this stagewas 0.076. In addition, the phaseof the reflection408 (E : Sincethe number of variableparameters was too 2.58)was found to be 0o, usingthe ), relationship. large,the final least-squaresrefinement of the struc- The phasesof the following five reflectionswere rep- ture using anisotropictemperature factors was car- resentedby symbols: riedout by theprogram Cnvr-se (Stewart et al.,1972) in blocks,one block being assigned to eachatom. The Final atomic scatteringfactors for Na, Ca, RE, Si, O, and hkl E phaseangle F weretaken from Cromer and Mann (1968)and 2 0-4 4.01 00 corrected for anomalous dispersion(Cromer and 4 t2-4 3.21 1800 Liberman, 1970). The observed structure factors 890 2.55 00 (.Fo's)were weighted by the formula l/o2(Fo), where 6-60 2.37 1800 o(Fo) is the standarddeviation of the measurement 7 4-4 2.34 00 of .Fo, as determinedfrom the counting statistics. GHOSE AND llAN: AGRELLITE 565

Table 2. Agrellite:positional and thermalparameters and siteoccupancies (with standarddeviations in parentheses)

u22 *33 '12 *13 u^^ Atom ,LL ZJ ca(1A) 0.99796(r4) 0.215s4( s) 0.99620(15) 1,16(3) 16s( 5) e3( 4) 90( 3) -o( 4) 72( 3) 2s< 3) Ca(1B) 0.54L76(L2) 0.2846L( 4) 0.01966(13) 0.92(3) r42( 4) 76( 4) 83( 4) 3( 3) 66( 3) 18( 3) ca (2A) 0.4552r(r2) 0.72007( 4) 0.48010(13) 0.94(3) 133( 4) 85( 4) 8e( 4) 1( 3) 71( 3) 2r( 3) ca (28) 0.0015s(13) 0.78166(5) 0.s0022(14) L.27(3) re4( 4) r0r( 4) L24( 4) 14( 3) 108( 3) 27( 3)

Na(A) 0,23539(28) 0.99102(1r) 0.86794 (34) 2.49(7) rsl( 9) 287(L2) 286(11) s( 8) 80( 8) 2e( e) Na (B) 0.26L04(29) 0.50234(r2) 0.13576(36) 2.84(8) 139( 9) 370(13) 33r(12) -3( e) 74( e) 40(10) s1(1A) 0.20870(16) 0.93103(6) 0.35569(17) 0.81(3) 106( s) 6e(s) 76( s) 8( 4) 51( 4) 27( 4) si(18) 0.30739(16) o.s6807(6) 0.6ss42(18) 0.79(3) 10s( 5) 70(5) 83( 5) L2( 4) 54( 4) 28( 4) si(2A) 0.48573(16) 0.877e5(6) o.2t317(r7) 0.80(4) 108(s) 82( s) 63( s) -1( 4) s6( 4) 20( 4) si(2B) o.02460(16) 0.61933(6) 0.79391(r7) o.75(4) 93( s) 78(s) 74( 5) -o( 4) 46( 4) 18( 4) si(3A) 0.16705(16) 0.08998( 6) 0.33394(17) 0.78(3) 92( s) 77(s) 14( 5) s( 4) 48( 4) 23( 4) si(38) o.67404(76) o.s9o22(6) 0.34109(17) 0.7s(3) 87(5) 70(s) 8s( s) 6( 4) 45( 4) 2r( 4) si(4A) 0.48619(16) 0.8777r( 6) 0.71341(r8) 0.80(4) 107( s) 7s( 5) 68( 5) -4< 4) ss( 4) 2r( 4) si(4B) 0.02139(16) 0.61974( 6) 0.23430(18) 0,72(4) 94( 5) 81(s) 67( 5) 2( 4) s0( 4) 23( 4)

F(A) 0.7607(4) 0.76r0(2) 0.1268(s) 2.7(L) 170(14) 243(r7) 423(L9) -2(L2) 117(13) 82(14) F(B) 0.2353(4) 0.24sL(2) 0.3s9s(s) 2.5(r) 180(14) 223(l-6) 356(r7 ) -3 (r2) 69(13) 3(r3) o(1A) 0.3493(4) 0. 93s1(2) 0.6138(s) 1.3(1) 167(15) 117(1s) 79(13) 8(11) 32(11) 29(Lr) 0(18) 0.1641(4) 0.s639(2) 0.3974(s) 1.3(1) r70(15) 111(15) 85(13) 3s(r1) 28(1r) 38(11) o(2A) 0.1028(4) 0.0048(1) 0.3023(s) 1.1(1) 143(14) 77(r4) L22(L4) 19(11) 76(11) 29(r1) o (28) 0.s891(4) 0.506s(1) 0.2960(s) 1.0(1) r07(14) 66(13) 148(14) 13(ro) s8(11) 26(r1) o (3A) 0.3483(4) 0.9352(2) 0.2356(5) r.2(1) 182(15) lls(1s) rs3(15) 24

Site Ca R.E. Site Ca PF Ca(1A) 0.8534 0.1466(6) ca(18) 0.978 0.022(2) Ca(2A) 0.993 0,007(2) ca(28) 0.985 0.015(2)

Form of the anisotropic temperature factor (x102): expl-2r2(urrhzaoz + rrrk2bo2 + u33t2.o2 * 2u.rhkaxbxcos1x

+ 2uL3ht"axc*cosBx + Zurrktbxcxcoso*) I.

Five cyclesof refinementreduced the R factor to the estimated standard deviations in bond lengths and final valueof 0.045for 5343reflections. The final angles include the standard deviations of the mea- occupancyfactors, positional and thermal parame- surement of the unit-cell dimensions.The average tersare givenin Table 2 and a list of observedand deviations in Na-O, Ca-O, and Si-O bond lengths calculatedstructure factors in Table31. Bond lengths are 0.004,0.003, and 0.0034, and in O-Na-O, O-Ca- and angles(Tables 4, 5, and 6) havebeen calculated O and O-Si-O angles0.l,0.1,and 0.20 respectively. usingthe program BoNu-n (Stewart et al.,1972).The Pseudosymmetryand atom nomenclature 'To Gittins et al. (1976) proposed an alternative obtaina copy of this table,order DocumentAM-79-101 from the BusinessOffice, Mineralogical Society of America,2000 pseudomonoclinicC-centered unit cell for agrellite, FloridaAve., N.W., Washington,D.C. 20009.Please remit $1.00 with double the volume of the triclinic cell.We note a in advancefor the microfiche. strong tendencytowards C-centeringin terms of the 566 GHOSE AND WAN: AGRELLITE

Table 4. Agrellite: interatomic distances(A) and angles (") within Table 5. Agrellite: interatomic distances(A) and angles(') within the Ca-polyhedra (with standard deviations in parentheses) the Na-polyhedra (with standard deviations in parentheses)

rh" C Na(B)- Po

ca(1A) -E (A) 2.400(4) ca(28) -F (A) 2.444<3) A B ca(1A)-F(B) 2 - 409(3) ca (28) -F (B) 2.464(4) ca(1A)-0(4A) 2.309(3) ca(28) -0(4A) 2.337(L) Na-0(1) 2.s71-(s> 2.578(5) 0 (1) -Na-0(2) 110, r06.9( ca(1A)-0(5A) 2.708(3> ca (28) -0 (10A) 2.720(3) Na-0(2) 2.353(4) 2.27o(4) 0(1)-Na-0(3) 1r5. 115, ca(lA)-0(5B) 2.49s(4) ca(28)-0(sB) Na-0(3) 2.568(4) 2.564(4) 0 (1) -Na-0(6) 58,6( 59.0( 2.562(3> -) ca(u)-0(8A) 2.395(4) ca(28)-0(8A) 2.430(4' Na-0(6) 2 606(4, 2.s97(4) 0(1) -Na-o (5 98.8( ca(14)-0(9A) 3.066(3) ca(2B) -0(7A) Na-o(6-) 2.50r(3) 2.408(L) 0(1)-Na-o(7) 70.8( 59.3( 3.107(4) '75.2( ca(1A)-0(108) 2.476(3, ca(28) -0 (10B) 2.532(4) Na-o(7) 3.102(4) 2-897(4) 0(l) -Na-0( 8) 78.7( Na-0(8) 2.603(4) 2.937(4) 0 (1) -Na-O (9) 148.8( r53.2( Mean of 2Ca-F Na-0(9) 3.102(4) 3.011(4) 0(2) -Na-o(3) r10.9( 104.7( disEeces 2.405 2.454 Mean 2.676 2.6s8 0(2) -Na-O(6) r44.7( L37.7 ( Mean of 6Ca-0 0 (2) -Na-0( 6-) r27.3( r31 .7 ( distances 2.575 2.615 0 (1)-0(6) 2.536(4' 2.s48(4) 0 (2) -Na-O(7) 93.1( 98,8( 0(1)-0(7) 3.317(5) 3.12s(5) 0(2) -Na-o(8) 62.9( 58.9( o(sA)-0(4A) 3.239(5) 0(10A)-0(4A) 3.250(4) 0 (1) -0( 8) 3.281(5) 3.379(A) 0(2)-Na-o(9) 93.5( 95.8( 0(5A)-0(10B) 3.141(s) 0(10A)-0(10B) 3.22r(4) 0 (2)-0(7) 2 634(4) 2 617(4) 0(3) -Na-o (6) 58.6( -0 -) 0 (5A) (sB) 3 .077(4) 0(10A)-0(sB) 3.148(s) 0(2)-0(8) 2.s93(4) 2.624(4) 0(3) -Na-0 (6 95.9( 0(sA)-0(8A) 3.436(5) 0(104)-0(8A) 3.439(4) 0(2)-0(9) 2.638(5) 2.524(5) 0(3)-Na-0 (7) r48.8( L52.9( -0(108) 0(4A) 3.152(4) 0(4A)-0(108) 3.1s2(4) 0 (3)-o (6) 2.532(6' 2.554(4) 0( 3) -Na-0(8) 78.9( 75.2( 0(10B)-0(sB) 3.3s6(s) 0(10B)-0 (58) 3.631(4) 0(3)-0(8) 3.286(4) 3.37L(4) 0(3)-Na-0(9) 70.9( 69.1( 0(5B)-0(8A) 3.348(4) 0(58)-0(8A) 3.348(4) 0(3)-0(e) 3.317(5) 3.183(5) 0(6)-Na-0(5') 88.6( 87.6( 0(8A)-0(4A) o(6)-o(6 3.567(4' 3.568(4) 0(6)-Na-O(7) r11.8 ( 3.s13(5) 0(8A)-0(4A) 3.501(s) -) 1 1lo.o( F(B) -F(A) 3.415(4) F(A) -F(B) 3.578(4) 0(6 -0 (7) 4.135(4> 4.963(6) 0(6) -Na-o(8) 81.2( 78.8( -0(9A) F(A) 3.329(s) F(A) -0(7A) 3.374(s) 0(6')-0(9) 2.559(6) 2.s50(6) 0(6) -Na-0(9) 111.7( 110.2( 0(9A)-F(B) 2.963(5) F(B) -0(7A) 3.009(s) 0(6-)-Na-o(7) s3.0( 56 4( F(B) -0(5B) 2.699(4) F(B) -o(sB) 2.69e(4) 0(6-) -Na-0(8) 169.8( 166.4( -0(8A) -Na-0(9) F(B) 2.123(4) F(B) -0(8A) 2 723(4\ 0(6-) 53.0( s4.8( -Na-0 0 (9A)-0 ( 84) 2.667 (5) 0(7A)-0(8A) 2.673(1) 0(7 ) (8) r31.2( r29.6( 0(9A)-0(4A) 3.391(s) 0(7A)-0(4A) 3 386(6) 0(7)-Na-o(9) 88.7( 95 2( -Na-0 F(A) -0(4A) 2.130(4) F(A) -0(4A) 2.130(4) 0(8) (9) 131.5( L29 .3 ( F(A) -0(10B) 2.765(4) F(A) -0(108) 2.765(4'

F(A)-ca(1A)-F(B) e0.5(1) F(A)-ca(2B)-F(B) e3.5(1) F(A)-ca(1A)-0(4A) 70 8(1) F(A)-ca(28)-0(4A) 69 6(1) F(A)-ca(1A)-0(5A) 135.s(1) F(A)-ca(28)-0(10A) 134.7(1) measuredX-ray intensitiesbased on the triclinicunit F(A)-ca(1A)-0(5B) r27.0(D F(A)-ca(28)-0(sB) 130.7(r) F(A)-ca(1A)-0(8A) 130.8(1) F(A)-ca(28)-0(8A) r29.9(L, cell. This pseudo-C-centeringis clearly manifest in F(A)-ca(IA)-0(I0B) 69.1(1) I(A)-ca(28)-0(10B) 57.5(L) E(B)-ca(IA)-0(4A) 140.3(1) F(B)-ca(2B)-0(4A) 139.3(t) termsof the positionalparameters of all the atoms, F(B)-ca(1A)-0(54) 131.9(1) r(B)-ca(28)-0(r0A) 130.s(1) F(B)-ca(rA)-0(sB) 66.8(1) I(B)-ca(28)-0(58) 64 9(I) exceptfluorine. The atomsso relatedhave been desig- F(B)-ca(1A)-0(8A) 69.0(1) F(B)-ca(28)-0(8A) 67.6(1) F(B)-ca(1A)-0(eA) 64.2(7\ F(B)-ca(28)-0(7A) 64.2(I) natedas A and B (Table2). The sodiumpolyhedra F(B)-ca(tA)-0(10B) 724 2

?he Ca(24) PaLAheC"ffi Ihe Ca(18) PoLlhedron Descriptionof the structure ca(2A) - I(B) 2.L92(3> ca(lB) -F(A) 220L(3) ca(2A) - 0(4B) 2.346(3) ca(1n) - 0(48) 2.326(3> ca(2A) - 0(5A) 2.408(3) ca(IB)-0(5A) 2387(4) The crystal structureof agrelliteconsists of (a) ca(2A) - 0(8B) 2.350(4) ca(1n) - 0(88) 2.338(3) ca(2A) - 0(r0A) 2.392(4\ ca(rB) - 0(10A) 2.316(3) silicatetubes crosslinked by sodiumatoms into so- Ca(2A) - 0(108) 2.4o1(3) ca(18) - o(sB) 2.408(3) Meanof 5Ca{ 2.381 2 -367 dium silicatelayers, and (b) calciumpolyhedral lay- distances ers,both parallelto the(010) plane, alternating along F(B) - 0(48) 3.424(5) F(A) - 0(4B) 3.5rs(4) F(B)-0(5A) 3335(5) F(A) - 0(10A) 3.163(4) the b axisto form a three-dimensionalframework. F(B) - 0(88) 3.27s(4' F(A) - o(5A) 3.203(s) r(B) - 0(10A) 3.270(5' F(A) - 0(8B) 3.361(5) 0(10B) - 0(48) 3.305(4) 0(58) - 0(48) 3.117(5) 0(108) - 0(88) 3,446(5' 0(5B) - 0(10A) 3.148(5) The silicate tubes 0(108) - O(sA) 3.141(5) o(sB) - 0(5A) 3.077(4) 0(108) - 0(104) 3.22r(4> 0(5B) - 0(8B) 3.410(4) The silicatetube consistsof two centrosymmet- 0(48) - 0(88) 3.446(5) 0(48) - 0(104) 3.152(4) 0(88) - 0(5A) 3.192(4) 0(10A) - 0(sA) 3.380(5) rically-relatedsingle silicate chains; each single chain 0(5A) - 0(104) 3.606(5) 0(sA) - 0(8B) 3,792(4' 0(10A) - 0(48) 3.152(4) 0(88) - 0(4B) 3.446(5) is formed by corner-sharingfour-membered tetrahe- I (B)-ca(2A) -0 (4B) 97.9(1) F(A)-ca(1B)-0(48) 101.8(r) dral rings in Figs. la,bl and F(B)-ca(2A)-0(5A) 92.8(1) F(A)-ca(18)-0(sA) 88.5(1) tsi(l)-Si(2)-Si(3)-Si(4) F(B)-ca(24)-0(88) 92.2(I) F(A)-ca(18)-0(88) 95.5(1) is the sameas the chainfound in vlasovite, F(B)-ca(2A)-0(10A) 90.9(1) I(A)-ca(18)-0(10A) 87.4(r) [Sinor'] F(B)-ca(2a)-0(10B) 171.9(10) r(A)-ca(18)-0(sB) 164.3

Table 6. Agrellite:Si-O bond distances(A) and angles(") (with (4')-Si(2')-Si(3')and Si(3)-S(4)-si(2)-Si(3')-S(l)- standarddeviations in parentheses) Si(4')-Si(2')-Si(l')in Figs. la,bl, which have four fhe Si(7A)- atu7 5i(18)- Tetmhedtv tetrahedrain common.There are two crystallograph- AB B ically-distinctsilicate tubes (A and B), whoseconfig- sr (1)-0 (1) 1.634(3) 1.637(3) o(1)-si(1)-0(2) 105.6(2) 104.8(2 ) si (r) -o (2) 1.633(3) 1.638(3) o(1)-si(1)-o(3) 107.s(2) 108.0(2) urations are only slightly differentfrom eachother. sl (1)-o (3) 7.639(4) L.631(4) 0(1)-si(r)-0(4) rr2.6(2) rr2.3(2) parallelto the c axisand are si (1)-0 (4) 1.s68(3) 1.s67(3) o(2)-si(1)-o(3) 105.3(2) 705.2(2) Thesesilicate tubes run Mean 1.619 t.620 o(2)-si(r)-o(4) 113.r(2) i3 1(2) in the(001) plane (Fig. 2). 0(3)-si(1)-o(4) 112.1(2) 772.3(2) hexagonallyclose-packed o(1)-o(2) 2.603(4) 2.595(4) Mean 109.4 109.4 o(1)-o(3) 2.639(5) 2.648(5) The sodiumsilicate layers o(1)-o(4) 2.665(4> 2.662(4) 0(2) -0 (3) 2.602(5) 2.60r(5) o(2)-o(4) 2 67rG) 2-684(4) The silicatetubes occur in layers parallel to the o (3)-o (4) 2.661(5) 2.661(s) Mean 2.640 2-642 (010)plane. Within eachlayer they arepacked in a staggeredfashion, leaving cavities at the boat-shaped Ihe Si(2A)- drkl Sil28)- ?etrahed?a eight-memberedrings. The sodium atoms occur AB B coordination(Figs. si(2)-o(3) r.630(4) r 643(4) o(3)-si(2)-o(5) r72.3(2) 112.0(2) within thesecavities in eight-fold si(2)-o(5) 1.s83(3) 1.583(3) 0(3)-si(2)-o(6) 10r 8(2) 102.1 (2) The Na(A)06 and Na(B)O' polyhedraare dis- si(2)-o(6) 7 634(4) r.642(4) o(3)-s1(2)-o(7) r08.s(2) 108.0(2) 3a,b). si(2)-o(7) 1.625(3) 1.613(3) 0(5)-si(2)-o(6) 1ls 3(2) 114.5(2) torted cubeswith very similar configurations;the av- Mean 1.618 7 620 o(5)-si(2)-o(7) rr4 .4(2) 116.3(2) 0(6)-si(2)-o(7) 103 4(2) 102.8(2) erageNa-O distancesare 2.676and 2.6584respec- 0(3)-o(5) 2.668(4) 2.674(s) Mean 109.3 109.3 o(3)-o(6) 2.532(6) 2.ss4(6) tively. Within these two polyhedra,the average o (3) -o (7) 2.642(4) 2.634( 4) o(5)-o(6) 2.7r8(5) 2 712(5) variationin correspondingNa-O bond lengthsand o(5)-0(7) 2.691(4) 2.714(4) o(6)-o(7) 2 s58(4) 2-544(4) O-Na-O anglesare 0.0834 and 3.lo respectively Mean 2.636 2.639 (Table5). Eachsodium polyhedron shares six corners with the silicatetube below and two with the silicate The Si(sA)- an!1 Si(38)- IetTahedra tube above.In addition,two sodiumpolyhedra oc- ABA B sideof a silicatetube share a poly- si(3)-0(2) r.637(3\ r.645(3) 0(2)-si(3)-0(7) 107.8(2) 706.6 (2) curringon either si(3)-0(7) 1.623(3) 7.62r(3) 0(2)-Sr(3)-0(8) r07.1(2) 108.9(2) hedral edge thereby forming a dimer. si(3)-0(8) 1.s8s(3) r.580(3) 0(2)-si(3)-0(9) 7O1.7(2) 106.8(2) [0(6)-0(6')], si(3)-0(9) r 629(4) r.625(4) 0(7)-Si(3)-0(8) 1r2 B(2) 113,9(2) Two crystallographicallydistinct sodium silicate lay- Mean 1.619 1.618 0(7)-Si(3)-0(9) 109.0(2) 707.9(2) 0(8)-si(3)-0(9) 112.1(2) 1r2.4(2) ers(l and B), parallelto the (010)plane, with very o(2)-o(7) 2-634(4\ 2-611(4) Mean 109.4 709 4 o(2)-0(8) 2.593(4) 2 624(4\ similarstereochemical configurations are formed this 0(2)-0(9) 2.638(s) 2-624(5) o(7)-0(8) 2.673(4) 2.683(4) way(Figs. 3a,b). 0(7)-0(9) z.648(s) 2.624(5) 0(8)-0(9) 2.661(5) 2.663(5) Mean 2 642 2.639 The calciumpolyhedral layers

The 5i(4A)- ar"C Si(48)- Ietruhedra Both calcium atoms, Ca(lA) and Ca(2B), are

AB B coordinatedto six and two fluorine atoms si(4)-0(r) 1.63r(3) 1.638(3) 0(1)-si(4)-0(6) r01.7(2) r02.2(2' each.The irregularcoordination polyhedron consists si(4)-0(5) r.639(4\ 7.637(4) 0(1)-Si(4)-0(9) 108.4(2) 107.7(1) si(4)-0(e) r.624(4) r 6rs(4) 0(1)-si(4)-0(10) 112.6(2) r12 3(1) of two parts, (a) a square-pyramidformed by five s1(4)-0(10) 1.s8s(3) r.s82(3) 0(6)-si(4)-0(e) 103.3(2) 1033(2) Mean I.620 1.618 0(6)-si(4)-0(I0) 115.4(2) r74.5(2) oxygenatoms, and (b) two fluorine atomsand an 0(1)-0(6) 2.536(4) 2.548(4) 0(9)-si(4)-0(10) 114.4(2) rr4.9(2) 0(1)-0(9) 2.640(4) 2.639(4) Mean 109.3 ro9.2 oxygen atom at the corners of a triangle occurring 0(1)-0(10) 2 676(4\ 2.674(4) 0(5)--0(9) 2.559(6\ 2.ss5o(6) above the equatorialplane (Fig. 4). Within the o(6)-o(10) 2.725(4) 2 707(4) o(9)-o(10) 2.698(4) 2 695(4) Ca(lA)OuF,and Ca(2B)OuF, polyhedra, the averages Mean 2-639 2.636 of 6 Ca-O distancesare 2.575 and 2.615Aand the

Si-Si dist@ces Si-O-SL dqLes averagesof two Ca-F distancesare 2.405 and 2.454A most of the ABAB respectively.The Ca(lA) site contains si(1)-si(2) 2.976(2)2.988(2) si(1)-o(1)-si(4) 13r.3Q) a32,7(2) rare-earthions (Table2). The Ca(2B)polyhedron is sic.)-s1(3) 3.049(2)3.013(2) s1(1)-o(2)-s1(3) 137.6(2)r33.2(2) slightlylarger than the Ca(lA) polyhedron;hence the r33.2(2) si(1)-si(4) 2,976<2)3.oOO(2) s1(1)-0(2)-s1(3) a37.6(2) former site may be slightlytoo largeto containa si(2)-si(3) 3.r29(2)3.126(2) si(2)-o(6)-si(4) r40.2<2)\40.7(2) sr(2)-s1(4) 3.078(2)3.088(2) si(2)-o(7)-si(3) 147.7(3)150.3(3) largefraction of the rare-earthions. The correspond- si(3)-si(4) 3.120(2)3.116(2) s1(3)-o(9)-sI(4)t'47.7(2) r48.2<2) ing O-Ca-O or O-Ca-F angleswithin the Ca(lA) Mean I39 ,2 139.4 and Ca(2B)polyhedra are very similar (av. deviation sition [SirOro],whose diameter is definedby a basket- 1.7') (Table4). Both Ca(2A) and Ca(lB) are sur- shapedsix-membered ring tS(2)-S(3)-Si(1)-S(4)- roundedby fiveoxygen and onefluorine atoms each Si(3')-Si(l') in Figs. 1a,bl. In addition each tube at the cornersof distortedoctahedra; the averagesof containstwo different boat-shapedeight-membered five Ca-O distancesare 2.381 and 2.3674,and the tetrahedral rings tSi(l)-S(4)-Si(2)-Si(l')-Si(3)-Si Ca-F distances2.192 and 2.201A, respectively. 568 GHOSE AND WAN: AGRELLITE

b

Fig. 1a'b' Agrellite: stereochemical configuration of the two crystallographically different [SLOro] double chains (tubes) A and B.

Again,the O-Ca-O andO-Ca-F angleswithin these on one sideof the calciumpolyhedral layer (set ofA two octahedraare remarkablysimilar (av. deviation )is slightlydifferent from thoseoccurring on 3.0")(Table 4). The Ca(2A)and Ca(lB) sitescontain the otherside (set of B oxygens).The sodiumsilicate very small amountsof the rare-earthions, which is layer,A, occursin betweentwo setsof A-layer oxy- consistentwith their smallerpolyhedral sizes. gen atoms,whereas the sodiumsilicate layer, ,8, oc- AlternatingCa(lA) and Ca(2B)polyhedra share curs in betweentwo sets of B-layer oxygen atoms. oppositetriangular faces [F(A)-O(4A)-O(l0B) and The sodium silicatelayers are connectedto the cal- F(B)-O(5B)-O(8A)l;likewise, Ca(2A) and Ca(lB) cium polyhedrallayers by sharingsilicate tetrahedral octahedrashare oppositeoctahedral edges [O(4B)- cornerswith thecalcium polyhedral corners (Fig. 5). O(l0A) andO(5A)-O(8B)1, thereby forming two dif- ferentpolyhedral chains parallel to the c axis,which alternatealong the a axis.Furthermore, the Ca(lA) Stereochemicalconfiguration of the and Ca(28)polyhedra share square-pyramidal edges silicatedouble chain (tube) lsisoro]t- with the octahedraledges [O(5A)-O(l0B), O(l0B)- The Si-O bond o(l0A), o(l0A)-O(5B), and O(58)-o(sA)l of the lengthsand Si-O-Si angles Ca(2A)and Ca(lB) octahedra,which result in a poly- The averageSi-O distanceswithin the eight crys- hedrallayer parallel to the (010)plane (Fig. a). tallographically-differentsilicate tetrahedra are re- markablyconstant, with a value of 1.619+0.001A. The thre e-di me ns io nal work frame The angulardistortions within the individualtetra- If we designatethe calciumpolyhedral layer as C hedraare comparable;the O-Si-O anglesvary from and its centrosymmetricequivalent ase, and thetwo 101.7to 116.3"(Table 6). differentsodium silicate layers as A andB, the stack- If we ignore the very long Ca-O or Na-O bonds ing sequenceof the layersalong the 6 axis is: AC- (>3.0A), the oxygenatoms can be dividedinto five BCACBC.. . , The configurationof theoxygen atoms groupsin termsof coordination: GHOSE AND WAN.' AGRELLITE 569

Coil8)

Co{rA)

o co(2A) o Co(2Bl

Fig.2. Agrellite:projectionofthesilicatetubesparalleltothecaxis; notethehexagonal close-packingofthetubesinthe(001)plane

Av. Si-O Av. Si-O-Si ated with C- and D-type bonds (140.5 and 132.9" Oxygentype bondlength (A) angle(') respectively). A:lSi * 3(Ca,Na) 1.583 A correlationof the largerSi-O-Si angleswith the B:lSi* 2Ca 1.568 shorter Si-O bond lengths and uiceuersq has been C:2Si-| 2Na 1.636 140.5 found through the molecularorbital calculationson D:2Si* lNa 1.637 132.9 silicatechain fragments(Tossell and Gibbs, 1977). E:2Sionly 1.622 148.3 Similar correlation has been observed in rosen- hahnite,CaaSigOs(OH ), (Wan et al., 1977),zektzerite, Within eachsilicate tetrahedron, there is one non- NaLiZrSieOru(Ghose and Wan, 1978b)and inesite, bridgingand threebridging Si-O bonds.As expected, CarMnrSi,oOm(OH)r.5HrO (Wan and Ghose, 1978). the non-bridgingSi-O bonds(Types A and B) are significantlyshorter than the bridging Si-O bonds with relatedstructures (TypesC, D, E). Sincethe B-typeoxygen atoms are Comparison bondedto two calciumatoms each in additionto one Silicatetubes with the composition[SirOzo] found siliconatom, they are charge-deficientas opposedto in agrellitehave been found previouslyin fenaksite, the A-type oxygenatoms, each of which is bondedto FeNaKSLOTo(Golovachev et al., l97l), litidionite, threecalcium and one siliconatoms. As a result,the CuNaKSLO,o(Pozas et al., 1975),and CuNazSi,O'o B-type Si-O bonds (av. 1.568,4')are significantly (Kawamuraand Kawahara,1977). In thesethree shorterthan the A-type Si-O bonds (av. 1.5834). isostructuralcompounds, [Sisoro]tubes are cross- Within the bridgingSi-O bonds,the E-typebonds linked by serratedchains of edge-sharingdimers of (av.1.622A)are significantly shorter than the C- and Fe- (or Cu-) squarepyramids alternating with dimers D-types(av. 1.636and 1.637,4'),which are nearly of edge-sharingNa-square pyramids. The potassium identical.The E-type bondsare also associatedwith atoms (likewise one set of sodium atoms in largerSi-O-Si angles(av. 148.3')than thoseassoci- CuNazSirOro)occur in cavitiescreated by the boat- 570 GHOSE AND WAN.' AGRELLITE

O(9al 3A)

(31

b )(88)

Fig. 3a,b Agrellite: views of the two crystallographically distinct sodium silicate layers, A and B, parallel to the (010) plane. GHOSE AND WAN: AGRELLITE 571

Fig. 4. Agrellite:a view of the calciumpolyhedral layer parallel to the (010)plane.

Fig. 5. Agrellite: a view along the a axis; note the stacking of the sodium silicate layers and the calcium polyhedral layers along the b axts. 572 GHOSE AND WAN: AGRELLITE

shapedeight-membered tetrahedral rings, and are Germain, G., P Main and M. M. Woolfson (1971) The appli- closelycomparable to the Na-coordinationfound in cation of phase relationships to complex structures III. The agrellite.However, in agrellitethere are two crys- optimum use of phase relationships. Acta Crystallogr., A27, 368-376 tallographically-distinctdouble chains,whereas in Ghose, S. and C. Wan (1978a)A new type of silicatedouble chain thesecompounds there is only one.This distinctionis in agrelfite, NaCarSi.O,oF. N aturwissens chaft e n, 65, 59. most likely createdby the differentcoordinatio'n re- - (1978b) Zektzerite, NaLiZrSi"O,u: a silicate with six-tet- quirementsof calciumand fluorineatoms in agrellite, rahedral-repeat double chains. Am. ., 6J, 304-310. as opposedto the transition-metalions in fenaksite Gittins, J., M. G Bown and D. Sturman (1976)Agrellite, a rock- and litidionite. forming mineral in regionally metamorphosed agpaitic rocks. Can. Mineral.. 14. 120-126. Liebau(1978) has termed the [Si6Oro]tubea "loop- Golovachev, V P., Yu.N. Drozdov, E. A. Kuz'min and N. V. branched dreier (three-tetrahedral-repeat)double Belov (1971) The of fenaksite. Souiet Phys.- chain."We wouldlike to emphasizethe tubular na- Dokl.. 15.902-904. tureofthese double chains and prefer to classifythem Karle, J and L L. Karle (1966)The symbolic addition procedure for phase determination for centrosymmetric and non-cen- in a group of structurescomposed of silicatetubes. trosymmetric crystals. Acta Crystallogr , 2l, 849-859. The other membersof this group are narsarsukite, Kawamura, K anC A. Kawahara (1977) The crystal structureof NarTiOSioO,o(Pyatenko and Pudovkina,1959; Pea- synthetic copper sodium silicate: CuNarSioOro.Acta Crystal- cor and Buerger,1962), canasite, CauNa.K2[Sir2Oso] logr.,833, l07l-1075. (OH,F)4 (Chiragov et al., 1969), and miserite, Liebau, F (1978)Silicates with branchedanions: a crystallochem- ically distinct class.Am. Mineral., 63, 918-923. KCau(SirO,)(Si6O,uXOH,F)(Scott, 1976). The sili- Peacor, D. R. and M. J. Buerger (1962) The determinationand catetube in narsarsukiteis definedby four-membered refinement of the structure of narsarsukite, NarTiOSiaO,o.,42. rings,whereas those in canasiteand miseriteare de- Mineral , 47, 539-556. finedby two differenttypes of eight-memberedrings. Pozas,J. M. M., G. Rossi and Y.Tazzoli (1975)Re-examination and crystal structure analysis of litidionite. Am. Mineral., 60, Acknowledgments 47t-474. Pyatenko, Y. U. and Z. V. Pudovkina (1959) Concerning the We are indebtedro P. J. Dunn, SmithsonianInstitution, for the crystal structure of narsarsukite. Sou. Phys Crystallogr., 12, donation of the agrellite crystal, and to Dr. Y. Ohashi, University 885-886. of Pennsylvania,Philadelphia, and Dr. S. Guggenheim,University Scott, J. D. (1976) Crystal structure of miserite, a Zoltai type 5 of Illinois at Chicago Circle, for critical reviews. This researchhas structure. Can. Mineral., 14, 515-528. been supported in part through NSF grant EAR 76-13373(Geo- Stewart,J. M., Kruger, chemistry). G. J. H. L. Ammon, C. Dickinson and S. R. Hall (1972) The X-nev Sysrepr-version of June, 1972.Tech. References Rep. TR-(92, Computer Science Center, University of Mary- land, College Park, Maryland. Bond,W. L.(1951) Making smallspheres. Reu. Sci. Instr., 22, 344- Tossell,J. A. and C. V. Gibbs (1977) Predictionof T-O-T angles 34s. from molecular orbital studies on corner sharing mineral frag- Chiragov, M. L, Kh S. Mamedov and N. V. Belov (1969)On the ments (abstr ). Trans Am. Geophys Union, 58, 522. crystaf structure of kanasite-CarNa.Kr[Si,rO xof(OH,F)1. D okl. Wan, C. and S. Ghose (1978) Inesite,a hydrated.calcium manga- Akad Nauk SSSR, .f85, 6'12-674(in Russian). nese silicate with five-tetrahedral-repeat double chains. lrn. Cromer, D. T. and D. Liberman (1970)Relativistic calculation of Mineral.,63, 563-571. - anomalous scattering factors for X-rays. "/. Chem. Phys., 53, and G. V. Gibbs (1977) Rosenhahnite, l89l-1898 CarSirOr(OH )r: crystal structure and the stereochemicalconfigu- - and J. B. Mann (1968) X-ray scatteringfactors computed ration of the hydroxylated trisilicate group, [SirOr(OH),]. Am from numerical Hartree-Fock wave functions. Acta Crystallogr., Mineral..62.503-512. A24, 321-324. Voronkov, A. A. and Yu A Pyatenko(1961) Crystal structureof Finger, L. W. (1969)Determination of cation distributionby least- vlasovite (in Russian). Kristallografya, 6, 937-943. squares refinement of X-ray data. Carnegie Inst. Wash Year Book, 67, 216-21'7. Fleet, S. G. and J. R. Cann (1967) Vlasovite:a secondoccurrence Manuscript receiued, January 12, 1978; and a triclinic to a monoclinic inversion. Mineral. Mag., 36,233- acceptedfor publication, December 19, 1978 241.