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Zektzerite, Nalizrsiuo,U: a Silicate with Six-Tetrahedral-Repeat Double

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Zektzerite, Nalizrsiuo,U: a Silicate with Six-Tetrahedral-Repeat Double American Mineralogist, Volume 63, pages 304-310' 1978 Zektzerite, NaLiZrSiuO,u: a silicate with six-tetrahedral-repeatdouble chains SusnA.rnGHosn nNo Cus'Nc Wa'N Department of GeologicalSciences, Uniuersity of Washington Sealt le. Washinston98 I 95 Abstract : zektzerite, Nal-iZrSiuo,u, is orthorhombic, space group Cmca, with cell dimensions: a 14.330(2),b : 17.354(2),and c : 10.164(2)4;Z : 8.The crystal structurehas been determinedby the symbolic addition method and refinedby the method of leastsquares to an R factor of 0.040for 2389reflections, measured on an automaticsingle-crystal diffractometer. The crystal structureof zektzeriteis a three-dimensionalframework consistingof (a) edge- sharing Na-polyhedral chains, (b) octahedral-tetrahedralchains, formed by alternating Li tetrahedra andZr octahedrasharing edges, and (c) corrugateddouble-silicate chains with six- tetrahedraf repeat (Seclrser-Doppelkette)and three different four-membered rings. The Li tetrahedron,with an averageLi-O distanceof 1.959A,shows strong angular distortion. The Zr octahedronis nearly regular,with an averageZr-O distanceof 2.0'/4A.The sodium atom occurs in an irregular cavity formed by the corrugation of the silicatedouble chains; it is coordinatedto six oxygen atoms at distancesof 2.37-2.6'7A,and four more oxygenatoms at distancesof 3.12-3.23A.The averageSi-O bond lengthswithin the Si(l)' Si(2)' and Si(3) tetrahedraarel.6l4,l.6l6,andl.6l0A.TheSi-O-Si bondanglesinvolvingoxygenslyingon mirror planesaverage 155.7", whereas those within the singlesilicate chain averagel4'7.6". The larger Si-O-Si anglesare associatedwith shorter Si-O bonds. Zektzeriteis isostructural with tuhualite, (Na,K)Fer+Fe3+Si"O,u,and synthetic Na2MgrSiuo,r. Provided the valence balanceand coordination requirementsare satisfied,a largenumber ofsilicatescan crystallize within this structuretype. Introduction Experimental ground Zektzerite,LiNaZrSi.O15, ? Il€w mineral found in A spherewith a diameter of 0 44 mm was grinder miarolitic cavitiesof the Golden Horn batholith near from a singlecrystal fragment usinga sphere Washington Pass,North Cascades,Washington, oc- (Bond, 1951). The single-crystalsphere was mounted curs in associationwith quartz, microcline, aegirine. on the computer-controlledautomatic single-crystal riebeckite, astrophyllite, zircon, and elpidite. It is X-ray diffractometer (Syntex PT), and the unit-cell least orthorhombic and occurs as translucent colorless dimensions were refined by the method of MoKa stout prisms. Dunn et al. (1977) determinedits opti- squares,using l5 reflectionsmeasured with (Table cal properties, unit-cell dimensions and possible radiation with20 valuesbetween 30o and 40" spacegroups; they also noted the similarity of its cell l). The unit-celldimensions are in good agreement (1977). dimensionsand chemicalcomposition with thoseof with those determinedby Dunn et al. The tuhualite,(Na,K)zFe7+Fe;+Si'rOgo. HrO. The present intensitiesof all reflectionswithin a 20 value of 65" structure determination shows that thesetwo miner- were measuredon the diffractometer,using MoKa from a als are indeedisostructural, containing double silicate radiation monochromatized by reflection chains with six-tetrahedralrepeat (Sechser-Doppel- graphite"single" crystal,and a scintillationcounter. being kette\.1 A variablescan rate was used,the minimum 2"/min (50kV, 12.5mA), Out of a total 2389reflec- 316 were below 3o(1),where o(1) is the stan- 1See [.iebau (1972) for the terminology and a classificationof tions, silicatestructures based on chain types. dard deviation of the measurementof the intensity,1, 0003-004x /78 /0304-0304$02.00 304 GHOSE AND I'YAN ZEKTZERITE Table I Zektzerite: crystal data culation basedon theseatoms followed by difference Fourier synthesisyielded the positionsof one silicon zektzerite, Naliz!si601s: barholith, N. cascades, positions $:1fl:l_lH" and two oxygen atoms. These atomic were refinedby the method of leastsquares. The difference Colorless. translucent DrisN Fourier synthesissubsequently calculated revealed Orthorhonbic, i@ ce1l volune: 2527.61.7)L3 the positionof the lithium atom. a(;) = 14.330(2) Cel1 conteoE: 8[NaLizrSiUOrrl All the atomic positionaland thermalparameters -3 b(L) = ri.3s4(2) D: 2.79ecm" were refined by the method of full-matrix least m- -1 squaresusing the RrtNe program(Finger, 1969). The cti; = 1s.1641r, D: 2.80scn- c- observedstructure factors (Fo's)were weightedby l/ group: Space Clnca U(l4cK0): 15.409 cn-1 6t(F.), whereo(F") is the standarddeviation of Fo,as determinedby the counting statistics.The atomic as derived from the counting statistics.The intensity scatteringfactors for Li, Na, Zr, Si, and O weretaken data werecorrected for Lorentz and polarization fac- from Cromer and Mann (1968),and correctedfor tors. No absorptioncorrections were made, sincethe anomalousdispersion (Cromer and Liberman,1970). linear absorption coefficient of zektzerite for MoKa Three cyclesof refinementusing anisotropic temper- ature factors yielded a final R-factor of 0.040 for all radiationis small (Table I ). reflections.40 strong low-angle reflections(with F,- Determination and refinementof the crystal structure F. > 10.0 were believed to be suffering from ex- Dunn et al. (1977)could not distinguishbetween tinction and were excludedfrom the refinement.The the two possiblespace groups Cmca and C2ca. The refinementconverged at this stage,the averageshift Wilson statisticsof the measuredintensities indicated u.r.error being0.00. The final atomic positionaland the presenceof a centerof symmetry and Cmca as the thermal parametersare listed in Table 2. Observed correct spacegroup. The crystal structure was deter- and calculatedstructure factors are listed in Table 3.'z mined directly by the syinbolic addition method The bond lengthsand angles,and the dimensionsof (Karle and Karle, 1966),using the computer program '?To obtain a copy of this table, order Document AM-78-065 MurrnN (Germain et al., l97l). The first E-map from the BusinessOffice, MineralogicalSociety of America, 1909 showedthe positionsof the sodium,zirconium, two K Street,N.W, Washington,D C. 20006 Pleaseremit $l 00 in silicon,and sevenoxygen atoms. Structure-lactor cal- advancefor the microfiche Table2 Zektzerite:atomrc positional and thermal parameters(standard deviations in parentheses) Atom B eqt -11R* 8,, R Btz 9u Bzt Na 0.25000 0. 21648(8) 0.25000 2.10(3) 25L(7) 78(4) 799(L7) 0 2o9(L) 0 -2(20) Li 0.247t2(44) 0. 00000 0. 00000 1.12(8) L52(22) 107(15) r9t (40) 0 o Zr 0.25000 -0.08805(1 ) 0.25000 0.38(r) s3(1) 29(r) 88(2) 0 -1 (1) 0 s1(1) 0.39091(4) 0.12869(3) 0.0r792(5) 0.s1(1) 59(2) 42(L) r2e(4) -6(2) -9(3) -r(2) si(2) 0.3896s(4) 0.07306(3) 0.31148(5) 0.51(r) 63(2) 41(r) L29(4) -8 (r) 2(3) -7(2) si (3) 0.39072(4) 0.19281(3) 0.s4143(5) 0.53(r) 67(2) 39(1) 137(4) -5(2) 7(3) -e (2) o(1) o.3707o(r2) 0.21970(8) -0.00542(16) L.2L(2) 222(8) 50(4) 28?G4) s (s) -2e(e) -4(6) 0(2) 0.32801(10) 0.07851(8) -0.07887(14) 0.73(2) 9e(6) s6(4) r72(LL) -15(4) -27(7) -4(s) 0(3) 0. 36177(11) 0. 11174(9 ) 0.17054(rs) L.02(2) 136(7) 102(s) r72(r2) 7(5) -3 (7) 3s(6) 0(4) 0.32978(10)-0. 00240(8 ) 0.34095(14) 0.79(2) L02(6) s3(4) 2L7(r2) -27 (4) 2(7) -10(s) 0(s) 0.36064(11) 0.14017(8) 0.4159r(15) 0.93(2) L36(7) 64(4) 22r(L3) -1 (4) 0(7) -50(6) 0(6) 0. 32984(1r) 0.1740s(8) o.66829(L4) 0.87(2) 121(6) 7L(4) 184(12) -16(4) s2(8) -3(s) 0(7) 0.50000 0. 11001(rs) -0.00132(24) r.33(4) 56(e) 170(8) 362(2L) 0 0 -31(1r) 0(8) 0.50000 0.0s683(13) o.3L7sr(24) 1.1s (3) 41(8) 115(7) 4L9(22) 0 0 -1(10) 0(9) 0.50000 0. 18146(14) 0.5708r(2s) 1.34(4) 72(9) 148(8) 4OO(22) 0 0 25(10) T. Equrvalenc tsocropac t, calcuiated from anisotropic temperatur^e factors 3J *Form of the (x105;: )1".i1 anisotropic temperature factor exp t r, L ;F; iJ u-u J-L 306 GHOSE AND WAN: ZEKTZERITE Table4 Zektzerite:interatomic distances (A) andangles (') (standarddeviations in parentheses) The Na ?oLghedron lhe Si(1) Tetrdhedron - - si(1) - o(2) 109.92(8) Na -- 0(3) 2,554(2)(x2) 9(l)-Na-0(3') s9.24(B) si(1) 0(1) 1.623(2) 0(1) - - si(1) - 0(3) 105.s7(8) Na - 0(5) 2.667(2)(x2) 0(3)-Na-0(s) 58.24(5) (x2) si(1) 0(2) 1.593(2) o(1) - - si(1) - o(7) 110.60(1r) Na - 0(6) 2.368(2)(x2) 0(3)-Na-0(5') 79.60(5)(x2) si(1) 0(3) 1.533(2) 0(1) - - sI(1) - 0(3) 1l-0.08(8) Na - 0(1) 3.r2o(2)(x2) 0(3)-tla-0(6) 99.04(s)(x2) si(1) 0(7) 1.608(1) o(2) - - 0(7) 111.38(10) Na- 0(1') 3.225(2)(x2) 0(s)-Na-0(6) 109.4s(s)(x2) Mean I.614 0(2) si(1) - si(1) - 0(7) 109.12(11) Meanof 6 2.530 0(6)-Na-0(6') 73.31(8) 0(3) L09.45 Meanof 10 2.787 0(1)-Na-0(1r) 109.76(5)(x2) o(1) - o(2) 2.633(2) Mean 0(1)-Na-0(3) 53.21 (4) (x2) o(1) - o(3) 2.593(2) - 0(3) - 0(3') 3.587(3) 0(1)-Na-0(5) 101.86(5)(x2) o(r) 0(7) 2.651(2) - 0(3) - 0(5) 2.542(2)(x2) 0(1)-Na-0(6) 54.97(4) (x2) o(2) 0(3) 2.644(2) - 0(3) - 0(5') 3.342(2)(x2) 0(1')-Na-0(5) 50.52(4)(x2) o(2) o(7) 2.645(2) - 0(3) - 0(5) 3.746(2)(x2) 0(1')-Na-0(6) 14 .67(5) (x2) 0(3) 0(7) 2.647(2) 0(5) - 0(6) 4.II4(2)(x2) Meas 2,636 o(6) - o(6') 2.821(3) 0(1) - 0(1r) 3.5I8(3)(x2) The Si(2) Tet"ahedran 0(1) - 0(3) 2.593(2)(x2) - si(2) - o(4) 11r.79(8) 0(t) - 0(5) 3.t04(2)(x2) si(2)-0(3) 1632(2) 0(3) - - o(s) 102.44(8) 0(1) - 0(6) 2.6re(2)(x2) si(2) - 0(4) 1.594(2) o(3) si(2) - - - 0(8) 110.27(11) 0(1') - 0(s) 2.564(2)(xz) si(2) o(5) 1.630(2) 0(3) si(2) - si(2) - 0(8) 1.607(r) o(4) - si(2) - o(s) 10e.11(8) 0(1') 0(6) 1.460(2)(xz) - Mean I.6L6 o(4) - si(2) 0(8) 112.24(10) - si(2) - 0(8) 110.s7(10) :he L1 lefrahe@on 0(s) o(3) - o(4) 2.611(2) Mean 109.40 Li - 0(2) 1.950(4)(x2) 0(2)-Li-0(2') 0(3) - 0(5) 2.542(2) Li - 0(4) 1.957(4) (x2) 0(2)-Li-0(4)
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