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MARIALITE:RIETVELD STRUCTURE-REFINEMENT and Asi MAS and 27AISATELLITE TRANSITION NMR SPEGTROSCOPV

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MARIALITE:RIETVELD STRUCTURE-REFINEMENT and Asi MAS and 27AISATELLITE TRANSITION NMR SPEGTROSCOPV 1039 The Canadian Mineralo gist Vol.34, pp. 1039-1050(19967 MARIALITE:RIETVELD STRUCTURE-REFINEMENT AND ASi MAS AND 27AISATELLITE TRANSITION NMR SPEGTROSCOPV ELENA V. SOKOLOVAT eru YtlRtr K. KABALOV Deparxnzntof Crystallography,Faculty of Geolog, MoscowState University,Moscow 119899,Russia BARBARA L. SHERRIFF AND DAVID K. TEERTSTRA Departurcntof GeolagicalSciences, University of Manitoba Winnipeg,Manitoba R3T 2N2 DAVID M. JENKINS Departmmtof GeologicalScimces and Envirownental Sndies, Binghamton University, Binghamtorl New York13902-6000, U.SA. GERALD KTINATH-FANDREI. STEFFEN GOETZ AND CHRISTIAN JAGER Institutfir Optik and QwmtenelelaroniltFriedrich-Schiller-Universitttt, Mat-Wien Platz I, D-07743Jena" Germany AssrRAcr The crystal structureof synthetic end-membermariatite (Ma) NaaAl3SieO2aCland three samplesof NaCl-rich scapolite from Pamir (central Asia) were refined using Rietveld methods. Compositional measulementsindicate meionite (Me) CaoAl6Si6OroCO3contents of 0 (SYN MAR), 4.6 (PAM-l), 7.5 (PAM-2), axld7.6Vo (PAM-3). The crystal structureswere - refined in spacegroup IAm using ionized X-ray scatteringfactors: Rp 4.89 - 5.92Vo,Rwp 6.78 - 7.28Vo,ls 2.53 3.4OVq, RF2.49 - 3.34Vo , s | .26 --2.O9. The syntheticend-member marialite has unit-cell parametena = 12.0396(2) A, c = 7.54n Q) A and V = 1093.3(4)Al. A linear conelation was found betweenthe a and c unit-cell dimensionsand the Si contentof these samplesof marialitic scapolite.Additional electron-densitymaxima were found on the differenceFourier maps D(xyz), and correlationwith an increasewith H2Ocontent suggests partial occupancyby H2Oalong the channelsofthe marialite framework. 27Alsatellite transition NMR spectrashow that Al is in only oneenvironment in the naturalsamples, and 2esi MAS NMR spectra show that Si alone occupiesthe Z1 site. Calculation of the numbersof A1-0-Si bonds from peak fitting to the 2esi NMR spectraindicate that up to 807oof the AI atomsin the T2 site are involved in one A1-O-AI bond. Keyword,s:scapolite, marialite, volatiles, synthesis,Rietveld refinement XRD, satellitetransition NMR, MAS NMR. SoMlaans Nous avons affin6 la structure cristalline de la marialite synth6tique(composition id6a1e:NaaAl3SbOr4Cl) et de trois 6chantjllonsde scapoliteproches de ce p61e,provenant des montagnesPamir, en Asie centrale,par m6thodesde Rieweld. l,a compositionde ces quatre6chantjllons, en termesde leur teneur en CaaAl6Si6O2aCO3,est 0 (SYN MAR), 4.6 (PAM-I)' 7.5 (PAM-2), andT.6Vo @AM-3). Leur structurea 6t6 affin6edals le groupespatial /4/m en utilisant desfacteurs de dispersion desrayons X appropri6saux espdcesionisdes: Rp 4.89 - 5.92Vo,Rwp 6.78 -7.287o, RB 2.53 -3.407o,Rp2.49 -3.34V9, s 1.26 - 2.O2, IE p6le marialite synthdtiquepossdde les paramdtresr6ticulaires suivants: a 12.0396(2),c 7.54nQ) A, V 1093.3(4)A3. Une relation lindaire existeentre les dimensionsa et c etle contenude Si. Des maxima en densit6d'6lectrons ont 616document€s sur des cartesde diff6renceFowier D(xyz); ceux-ci montrentune corr6lationavec la teneuren H2O,ce qui sembleindiquer une occupationpartielle des canaux dans 1atrame par des mol6culesde H2O. ks spectresde r6sonance magndtiquenucldaire (RMIrf dessatellites associ6s i la transitiondes atomes 7Al montrentque l'aluminium setrouve dansune seuleposition dansles &hantillons naturels.ks spectresRMN obtenuspar spin du 2eSil anglemagique montrent que seul le Si occupela position (1). Un calcul de la proportion de liaisons Al-O-Si par interprdtationdes pics d la lumibre desspectres RMN de 2esi indique qu'un maximum de 807odes atomesAl occupantla position Z2 seraientimpliquds dans une liaison Al-o-At. (Traduit par la R6daction) Mots-clds: scapolite,marialite, phase volatile, synthdse,affinement par m6thode de Rietveld, diffraction X, transition des satellites,r6sonance magn6tique nucl6aire, spin i anglemagique. IE-mnil address.'evsok@ geol.msu.ru 1040 Ivrnoluct:loN the A site of greater than 1.0 atom per formula unit (apfu), tf H2O is included with Cl-, CO32-and SOI- Scapolite-groupminerals have a general formula (Teertstra& Sheniff 1996b).The naturalsamples used M4T,O24A, and constitute a solid-solution series in this study were analyzed for H2O, and intensity betweenthe idealizedend-members NaoAlrSinOroCl peaksfound on difference-Fouriermaps from powder (marialite, Ma) and CaaAl6Si6O2oCO,(meionite, Me). XRD data are used to investigatethe position of the Scapolites have ttree main forms of isomorphous volatilespecies. substitution:Sia+ for Al3+in the Z site. Na+for Ca2*tn In this study, Rietveld structural refinementsof a the M site, Cl- for CO]- or SO?-in the A site. There syntheticsample of end-membermarialite and of three canalso be minor or traceamounts of K, Sr, Ba andFe, samplesof marialitewith meionitecontents of lessthan but only trace quantities of Mg, Mn,Ti, P, Br and F 8Voenable us to examinetrends in the cell parameters have been measured.Two changesin compositional for the marialitic portion of the scapolitesolid-solution and cell-parametertrends, at cation contents of series. Difference-Fourier maps are exarnined for Nar..Cao.uAlr.6Sis.o(Me1r) and Na,.4Car.6Al4.7Si7.3additionaldensity that would shedlight on the position (Me6) divide the seriesinto tlnee portions(Teertstra & of volatiles in scapolites.We studied the degree of Sherriff 7996a,Zo7otarcv1993). The Me < 15 portion Si-Al order in the tetrahedral sites with MAS and is the focusof this study. satellitetransition NMR spectroscopy. The role of volatile species,including HrO, within the scapolitestructure is not understood.There arefew Rsvrw oF TIIESTRUCTITRAL ANarvsss recent measurementsof volatile contents"because H and C can not be measuredusing the electron- Viewed along the c axis, the tetrahedral sites in microprobetechnique. Also, it is exhemely challeng- scapolite form two types of 4-memberedrings. One ing to find the position of these light atoms by ring consistsof Zl tetrahedrathat have their apices refinements of the structure using X-ray-diffraction pointing in the samedirection along the c axis. In the QRD) data.Although XRD datado not indicatewhere other ring, the apices of the tetrahedrapoint alterna- tfie H atoms are situated,infrared (IR) spectroscopic tively in opposite directions along the c axis. In the dataindicate the presenceof abundantbicarbonate and spacegroup IAm, with a 4-fold rotationaxis anda center bisulfate(Swayze & Clarke1990), and Raman spectra of inversion, the latter tetrahedraare symmetrically suggestthe presenceof HCI @onnay et al. 1978). equivalent,so arelabeled T2 (Fig.1), but in the space Formula calculationshave indicatedan anion sum for grolp P42ln,these become T2 arrd13. Viewed alons o cl,co3,so4 cl c%,so4 , a No,Co,K No,Cq, K Ftc. 1. Crystal structme of scapolite viewed (a) along the c axis and (b) along the a axis. The T2 autdT3 sites are equivalent in space goup l4lm. STRUCTTJRAL ASPECTS OF MARIALITE t04l the a axis, these rings join to form 5-membered the Al sites. Least-squaresfitting of the peaksin the rings and large cavities, which each enclose one 2eSi spectra gives the proportions of Si in different A anion surroundedby four alkefu(W cations.In the environmentsand allows the degreeof Si and Al order present study, the composition of the samples of amongthe tetrahedralsites to be studied. marialite will be quoted by their meionite content fVoMe= 100X divalentcations/41, and alsoby the Si ExpsRn/ENTALPnocEounrs contents(apfu). Teertstra& Sheniff (L996a)showed that variations Materials in the a and Vcell parameterscorrelate with Si:Al ratio rather than with substitutionsin the M or A site. There The naturalsamples of scapoliteare from the Kukurt is little overall variation of the c cell edge with hydrothermalscapolite deposit of fhe Muzcol'sk alpine compositionacross the series.Cell volumes(V = azc) metamorphiccomplex in the EasternPamir mountain seemto be constantover the rangeG-lSVoMe, because belt in Russia. This Paleozoic gneiss complex has with decreasingSi content,a decreasein a is matched experiencedamphibolite-grade metamorphism at the by a slight increasein c. core of an anticline, and arnphibolite-and greenschist- There has been one complete refinement of the grade metamorphismon the flanks. Scapotte is structureof a samplewith a meionite content of less widespreadthroughout the complex, associatedwith than l57o or Si greaterthan 8.4 apfu (Si: 8.7I apfu; zones of Na-metasomatism.The Kukurt deposit Belokonevaet al.1993); partiat data were reportedby consists of hydrothermal veins of scapolite with Comodi et al. (1990)for a samplewith Si = 8.47 apfu. cavities containing transparentcrystals of scapolite Single-crystalX-ray refinementsof the structureshow associatedwith rutile" iftnenite. titanite and albite. that intermediatemembers of the series obey space Scapolite also is found in secondarycavities within group P42ln, and that the end-membersobey I4lrn gfanitic pegmatitesalong the Turakuloma mountain (Belokonevaet al. L991,1993,Comodi et al. 1990, ridge (Zolotarev 1993, and referencestherein). The Papike& Zoltai L965,Lin & Burley I973a,b, 1975, scapolite crystals in the Kukutt deposit are usually Levien & Papike 1976,Papike & Stephenson1966, violet, although colorless and yellow crystals also Aitken et al. 1984,Ulbrich 1973a,b).In this study, occur. These crystals are usually prismatic, with the structuralrefinements derived from powderXRD data, dominantforms being {010} and {110}, but {120}, by the absenceof the weak reflectionsviolating body- {llll, {2211and {001} mayalso be present. centeredsymmetry, confirm
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