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 that the spacegroup l4lrn Three transparent violet-colored crystals of is correct for the long-rangesymmetry of marialite. inclusion-free, gem-quality, marialitic scapolite were Tbe T2 and 13 sitesin the spacegroup P4y'n become selectedfor study (PAM-l, PAM-2, PAM-3). The symmetrically equivalent n l4/rn, leading previous euhedralprisms, between 0.5 and 3 cm in length, show investigatorsto suggestthat, in contrastto mid-series a variation in the intensity of the violet color, PAM-2 scapolites,both end membersof the scapolite series being the darkest, and PAM-3, the lightest. The have a high degreeof Al-Si disorder.The changesof crystals were analyzedand checkedfor homogeneity symmetry occur near Me15 and Meur (Teerfstra & and purity by powder XRD, electron-microprobe Sherriff 1996a). It should be emphasizedthat in analysisand optical microscopy. compositionswith Me < 40Vo, Al-Si disorder is restricted to the T2 site, as the Z1 site is occupied Synthesisof marialite predominantlyby Si. )(RD observationsare consistent with a long-rangeaverage structural model. On a unit- Synthetic marialite was produced specifically for cell scale, transmissionelectron microscopy (TEM) NMR spectroscopicstudies in a piston-cylinder observationssuggest lower symmetry and Cl- and apparatusfrom a mixture of reagent grade Na2CO3, CO]- order(Hassan & Buseck1988). NaCl, Al2O3,SiO2, and Fe2O3.A preliminarylrllvp Magic angle spinning nuclear magnetic resonance investigation of the marialite synthesized,with the (MAS NMR) spectroscopyhas been used to investigate composition NaaAl3SieOraCl(without Fe), indicated the degreeof order of Si andAl in the tetrahedralsites, that extremelylong Z1relaxation times were neededto as it provides a short-rangeview of the structure acquirethe 2esi spectrum.Accordingly, a mixture was (Sheriff et al. 1987),but in that investigation,owing to preparedcontaining 0.1 wt.VoFe2O3 in order to induce the lack of Na- and Cl-rich samples,models of Al-Si a small amount of paramagneticFe into the marialite order had to be extrapolatedto the marialite end- structure to attempt to reduce the Z1 relaxation time member.Also, there was a problem with quadrupolar (e.g.,Sheniff & Hartrnan1985). If we assumethat all interactions causingbroad unresolvablepeaks in the of the Fe substitutesfor Al asFe3+ and that it remained 27Al spectra.In this sody, this problem is solved by as Fe3+,the composition of the resultant marialite using a combinedanalysis of the centraltransition and would be Naa.ssAlr.eeFee.elSie.q0O2acl;unfortunately, spiming sidebandsof the t l/2 = X 3/2 satellrte this Fe content was not confirmed by EMP analysis transitions, including their envelopes,to investigate (seebelow). 1042 THE CANADIAN MINERALOGIST
Rutherford mine, Ameta Courthouse, Virginia, anorthite from Sitkinak Island, Alask4 and tugtupite Saqle Codo StsdlS odslel T Cc) P(lb6) t(h) from the type localify in soutlem Greenland(R.O.M. checkedfor homogeneity MAR l-l! dde-N8(]@fi l0D(10) r72rt 45 M4 Qt4 Ab #M32790).Each samplewas MAR l-7 Ori&-NaClmir 1024(10) 16.(4) Ma. aE, Ab(?) by analysis. Compositions were determined on the MAR l-12 MAR l-ll tm3(r0) t73(3) M4 taal MAR 1-13 MAR l-7 103300) 17.q3) v) Me. IQtzl same samples from which the X-ray data were MAR2-I feneaiogorile 1Bq5) 1&6(4) 123 M4 halie, Qe measured.The elementsMn, Mgo Ti, P, Br and F - Nfl nii MAR2-2 Fe-bosiuSolide 180(5) r8.q4) q M!,hane,QE were sought, but not detected. - NaClBii MAR2-3 MAR2-I&Z-Z 1032(5) 18.1(4) t94 Mr. halnp Absolute quantities of HrO were determined at MAR 2-4 MAR 2-1 &2-2 1014(18) 18.3{3) 16r Mq ia&e, tQtzl 900'C by Karl Fischer titration using a Mitsubishi moisture meter for the three natural samples of I Al*rniatiw Abr alt'itc, Ma @irli!e, Qtd qurrta BtE l@b Mloab fis ee Fhe i8 Prior to the determination,the sampleswere FM itr tae ?,fuft. U@taiEi€€ h las digit @ g!@ tn!@ds. marialite. dried at 110'C to remove any water adsorbed on surfaces. The stoichiometric formulae for the four samples were calculated using the method of Teertstra & Sherriff (1996u b). This calculation consistsof four basic steps: (1) The formula of scapolite is initially The starting mixture was roasted in air at about calculatedby normalizing to Si + N = 12 apfu. 1100"C for 30 secondsto drive off CO. from the Monovalentand divalent cations(including total Fe as Na2CO3and to partially fuse the mixture. An additional Fe) are assignedto the M site. If XM is greaterthatr 15 wt.Vo NaCl was mixed into the decarbonated 4 apfu, this may indicate-thatsome of the Fez* tt M starting material in order to ensurethat the marialite should be assignedas Fer+ in Z. The forrnula can be is saturatedin NaCl. Portions of this mixture were renormalizedto Si + Al + Fe3+= 12, generatinga lower sealed(dry) in Pt capsulesand treated at l0l4-1030'C AuI. (2) An excesspositive charge(EPQ is calculated and 18.1-18.8kbar for 99-123 hours in a Vz-inch by subtractingthe negative charge generatedby the piston-cylinder apparatususing solid NaCl pressure framework (7O;) from the positive charge of the M media (Johannes1978). No specialattempt was made cations (M+) as follows: EPC = M+ - IQ = A-, w[s1s 'IOA= to control the fugacity of oxygenin the piston-cylinder N + Fe3+,andM+ = Na + K+2(Ca+ Mg + Sr pressureassemblage. + Ba + Mn + Fe2). (3) Cl and S contentsare usually High but incomplete yields of light blue-grey determinedby EMP analysis.By assuminga divalentS marialite were obtainedfrom this frst treatment.there species,the remaininganion-charge may be calculated being minor quartz and albite presentalong with the by subtracting Cl, F, and 25 from the EPC. Tllre excess NaCl. To maximize the yield of marialite, residual charge may be assigned to a divalently the material obtained from the first ffeatment was chargedcarbon species,grving a calculatedCO|- pfu. thoroughly ground and treated a secondtime at the (4) If H2O is determinedand there is a remaining samepressure-temperature conditions for an additional excesspositive chargeothis may be assignedas OH- to 161-194hours. This secondtreatment eliminated all of balancecharges. ff there is a net negativecharge, this the albite, and left only a trace (< l%o) of quartz, as may be assigned as H+ (i.e., bicarbonate).Any judged from the XRD powderpattern. The excessNaCl remainingH, when the chargesbalance, is assiguedas was rinsed from the sample with distilled water. molecularH2O. Examination of the marialite under the petrographic microscoperevealed blocky, equantgrains 25-30 p"m X- r ay p owde r diffractio n on a side,with low first-orderbirefringence and a mean index of refraction of 1.536. The conditions for the X-ray powder pat0ernswere collectedon an ADP-2 synthesisof individual runs and also the run products diffractometerusing CuKa radiation (Ni-filter), a step are given in Table 1. width of M0 of 0.02", a 2Q rangeof 10 to 150' and count times of 5 s per step. Chernicalanalyses Rietveld structure refinement The scapolitecrystals were mountedin epoxy resin, polishedand then analyzedusing a CAMECA SX-50 Structure refinements were carried out with the electron microprobe operating at 15 kV and 20 nA, Wyriet, version 3.3 program written by Schneider with a beam diameter 10 pm and count times of 20 s. (1989). The model of Belokonevaet al. (1993) for The data reduction usedthe PAP procedure@ouchou Mer1,with a spacegroup of I4/m. was usedas a base & Pichoir 1985). We used, as principal reference for the refinement of the three samplesfrom Pamir. standards,gem-quality meionite from Brazil, U.S.N.M. Later, for the sample of synthetic marialite #R6600-l (Dunn e/ al. 1,978),albite from the (SYN-MAR), the model for the Mea.6(PAM-I) was STRUCTTJRALASPECTS OF MARIALITE rM3 used. Two mixing parameterswere refined for the obtain these spectra with different relaxation delays pseudo-Voigtprofi.le functions, selectedusing six firll between pulses. The second set of sampleswas peak-widths at half maximum height @WHM), and prepared with the addition of Fe to try to increase the background was graphically modeled. Refined the relaxation rate. Even with the doped samplethe non-structural parameters included 20 zero point, relaxation rate was slow, and the best signal-to-noise sampledisplacement, profile parametenu, v, and w, ratio was obtainedwith 148transients and a 15-minute peak-asymmetrycorrections for 20 < 40o, and delay betweenpulses. preferred orientation. Scattering facton for ionized specieswere selectedfor the refinement of atomic RESULTS AND DISCUSSION coordinates, isotropic and anisotropic displacement factors.The occupanciesof Si wererefined at 7l = 8(fr) Chemicalcompo$itions and stoichiometricformulae and T2 = 16(r, as were thoseof Na, and Ca at the of the three natural and one synthetic samples of 8(ft) site. Tablesof structurefactors are availablefrom marialite are given in Table 2. T\e three samples the Depository of UnpublishedData, CISTI, National PAM-I, PAMJ and PAM-3 have compositions ResearchCouncil, Ottawa,Canada KlA 0S2. Mea.6,Me7.5 and M9.6, and the Si/Al values are 2.85, For comparative puqposes,the structure of the 2.72, and 2.71, respectively.It shouldbe noted that synthetic marialite was refined in the space group PAM-I and PAM-2 contain more K than PAM-3. P4t/n as well as I4/m. T\e reflections with h + k + Therefore, the low-Me PAM-I is mainly due to I * 2n, violating the body-centeredlattice, would be the high valuesfor K and the low levels of Ca rather expected if the structure obeys the space group than the high Na content Clable 2). SamplesPAM-I P4"ln. and PAM-2 have similar H2O contents,0.05 and After refinement, difference-Fouriermaps D(xyz1 0.06 wt.Vo.Although the stoichiometric calculations for the three natural samples indicated additional indicatethat this is in the form of HrO for PAM-I and intensity, which might representadditional positions OH- for PAM-2 to achievea balanceof charges,&ere for volatile speciesin the structure. may also be minor COi. PAM-3 has a much higher content with 0.16 'xt.Vo H2O distributed by charge- Nuclear magneticresonance spectroscory balance calculations between 0.08 OH pfu and 0.M H2Opto, or 0.08H2O and 0.04 CO3-. 2esi and 27Al MAS NMR spectrafor the samples PAM-I. PAM-2 and PAM-3 were obtained on a Bruker AMX400 instrumentat frequenciesof 79.5 and 104.2MHz, respectively.Rotation rates of 8-I4 Wz were obtainedusing a Bruker high-speedprobe. 2eSi spectra were recorded for PAM-I, PAM-2 and PAM-3 with recycle delaysof 5 s, asthis gavethe best signal-to-noiseratio for a given time-period. Spectra StO, (m%) 64.16 62l.3 6r:71 6Lv recordedfor PAM-I with recycledelays of 1, 5, 30 and Nro3 18.01 $62 1924 1931 180s showeddifferences in relative peak-intensitiesof F%o. 0.m 0.f7 0.6 ol}? less than !2Vo using these differing delays. Relative Na.O 14.60 t2,g t2.K tLw intensitiesof the 2eSipeaks were found by simulating r;o o.02 t37 1.48 0.94 0.05 1.15 192 LM the spectra on a computer using a least-squares sto 0.00 0.11 0.04 0.14 iterative process,which varied the isotropic chemical BaO 0.m 0.m 0.02 0.(B cl 4.lr 1,16 3,94 3.!lt shift, the Gaussianand Lorentzian broadeningpara- so3 0.m o.lz 0.15 0.16 meters, and the intensity of each line. Short pulses HrO d. 0.6 0.06 0.16 S@ r0.95 101.00 1m.90 10)96 correspondingto tip anglesof lessthan n/15 were used o4l,F 4g2 -.094 -o.t9 -{g) for 27Al in conjunction with a 1 s recycle delay. The Total 100.(p 1m.06 10.01 lq).06 baseline roll caused by the finite pulse-length and St (rptu) 9.4, E.EE 8.78 436 dead-time was corrected using the cubic spline fit N L98 3.12 32 324 Fc3' 0.m 0.m 0.0 0.01 in the spectrometersoftware (Kunath et al. 1992). Na 3.98 3.49 3.4t 353 The spectra were referenced against the 27AI(VI) 0.(! oa oz, 0.17 0.01 0.18 0a 0,9 resonanceof Y3A15O, at +0.7 ppm. Simulationsof the 0.m 0.01 0,01 0.m satellitetransitions were performedon a 486 processor cl 0.98 1.0r 095 0.96 (Kunath s 0.m 0.01 0.o2 0.u et al. L992)using the theory of Skibstedet al. OH rd. 0.m 0.06 0.6 (1991). HrO rd. 0.@ 0.m o04 zeSi svAr 3.@ 285 LN L1I spectraof the two samplesof syntheticmarialite M9 0.z) 4S 75 75 were obtainedat the Prairie RegionalNMR Centreon an AMX 500 with a Doty high-speed probe at a TtE Frp6d@ of lto, oI! Fe'4 a!iFe3' v@ €r€hr€d 6 d$lb€dh&em uLd frequencyof 99.35MHz. Many attemptswere madeto deb49d 1044 TT{E CANADLA.NMINERALOGIST
TA3LB 3. UNII- TABLB4. AToMIc cooRDNerss AND rrecroRs (41 TABLE j. sEr;ecrED INTERAToMTCDrsrANcEs (A AND ANGLESc) SYN-MAR SYN-MAR PAM-2 M, 0.3741(t 0375r(3) 0.3'125(9) vngo) , 02957 0.298(4) 03ql) 0r9ql) rOF(l) rJ84{t 1J6s{E) 1J5X8) 1J6X9 z OJ OJ OJ 0J roFc(l)' 1.608(t r.648(8) 1.@1(8) 1.628(8) B: 4s(2) 3.63(21 4,4Q) 3J(2) r(lF q4) x 2 L6Al4) 1.6D(5) r,63214) 1.635(0 aw t.612 1.618 1.(o5 r,617 rO) t 0.3386(3) 03fi€) 0.34G{9) Mmo) , 0,4rc7(2) 0.410(3) o.4rt4a o.Arno cxlFr0lql)' 110.(3) rn/g) 110.6(4) 10E2(4) 00 0 9^... o(rFr(lR4)x 2 [email protected]<2) rot.r(3) r10.1(3) 1093(3) BJ 1.05(E) 0.?1(t 1.8{2) ur(r, ql)_r(lH4)'x 2 1c9.3(2) 109.6(2) r09.0(3) 110.7(3) c(4Fr(1!-O(4)' lm.4@) u1.7(3) l0E.q2) 10E.6(3) rQ) t 0.661(3) 0.6611(2) 0.62r(5) 0.6611(t -** l09J 109J t@J l09J v 0.9154€) 0.9'5rQ' 0.9r4q5) 0.9141t 0.1936(3) OJ%W) 0.1qgT) 9?.3.13.(?, re>o\2) Lelg) r,6f,2Q) 1.65s(4) 1.6s8(4) B: 1.45(t 0J3(4) r2t1) u.t\rt r(2)_06) L64q4) 1.65r(t 1.64Xt 1.63XO r(2)q3) r.6zt(4') 1.649(t 1.668(t 1.659(0 o(1) , 0.45&(1) 0.4533(0 0.4570) 0.454{r) TQ>{x.4\ 1,659(4) 1,674(' 1.657(t 16521' t $sna 652{t 0.354{1) 035J(1) av@99 1.ils 1.659 1.656 1.651 00 0 0 Bl rJ(3) r.8(O 25(4) 1.1(4) aQYrQ)-q3') rvl.7Q) rut2Q) l0r.(3) 1o/.{3) 115J(3) 1143(3) 113.8(4) oQ) t o.@4(2t 0.69L(2) ocFr(2)-q3) Lr4242) 0.6909(?) 0.694(0 q2r-rQ)-q4) 1028(3) 162(3) 16.1(3) 0.8813(7) 0.880(t 0.88?.(8) 0,88r(r) 105.3(2) t 1121(3) l12J(3) 112,6(3) 2 00 0 0 o(3Fr(2)-o(3)' 110.4(2) 110.(3) B: r{3) rx(2) 1.4(3) 0.9(3) o(3Fr(2Fo(4) rrrxQ) 111.6(2) 10930) o{3Fr(2F(4)' rvts(2) lcrr36) rG.r(2) rt72(3) o(3) . 0.3538 03518(4) 0.3493(9) 03504(9) 8v@ge l@,4 109.4 [email protected] 109.4 v 0.9488 0.9485(4) 0.9501(9) 0.95d1) 0.7845(9) oJt 2{O a,7u{2) o.w)it M-o2 2AlXq 2394{E) 2.37(r) L4r(r) B: LW) 1.4{l) \4<3) l.(3) M43x 2 262l(5) 2&6) 2.ffiCn 2s76{n M-44 x 2 2.89q.4) ar/s(t 2.89qt 2910(t q4) t 0.?j91 02718(4) ozlM!7) 02.@4(9) M'&'x 2 3.m6(5) 3.03qO 3.015(0 LWA , 0.3729 Mn&3) 0.3't41Q) o3,fd6) M4 2,8r'.f/'4) 286qt 2,862!6) u893(6) 0.825q9) 0.e16(t 0.826(1) 0.8250) e@ge 2,799 2n5 2.1U 2m BJ 2-O{2) 15(2) 2.4(3) rJ(3) roplFr(1) 159.4(1) 159.(l) 159.4(1) 161.8(E) Clroj0J0J 0J r(2\42Yr?l !42,q.r) ,392q1) 141.400) 1413(3) roj0J0J 0J rQ)4$YrQ)' u0Jo) 148.0q9) 149.49(9' 148.9(3) zO30J0J 0.5 ?ol'o{4Fr@) 138.93(8) 136.9q8) 14018(8) 138.4(3) Br 33(2) 4J(5) 7,4' 4,9(4) av@ge u7.a 1460 t47,6 147.6 STRUCTIJRALASPECTS OF MARIALITE 1045 Y Y ]D f 1.0t 1.0 t- a 0.08 b o.42 Av Q *3:i! o.2o 0.6 a0.10 0 I o 6) o o.ro O0.36 Jo.+z @ 0 0 0.0t- 0.0 0.0 0.4 0.0 Y t c @0.20 00.30 00.20 L4) @0.:o o n a+, LY./ /Nl o o Frc. 2. Difference electron-densitymaps D(002) (0 < z < 0.5) @ for samplesof marialite PAM-I (a), PAM-2 O), PAM-3 o (c). The map valuesrange from 2.0 ta 2.587(PAM-I), 19 o I.7 to 2.553(PAM-2), 1.7 to 2.474(PAM-3). Contours 2.30 for 6\, aredrawn at valuesof electrondensity of 2.00 and v PAM-I, 1.70,2.00, and 2.30 for PAM-2 and PAM-3, with intervals of 0.3. The numberson the maps indicate 0.0F 0.0 the e value for eachmaximum. range from 2.0 to 2.587 (PAM-l), 1.7 to 2.553 channelsof fhe sfructureabove and below the A site, @AM-2), 1.7 ro 2.474 @AM-3). Figures2a, b and c which is most pronouncedin the H2O-rich sample summarizethe positions of electon-density maxima PAM-3. Othermaxima which do not haveany specific for PAM-I, PAM-2 and PAM-3, respectively. To spatialposition but alsoare situatedin the intersticesof removebackground noise and show the projectionsof the structure,occur for all thrce natural samples.All the intensemarima only, electron-densitycontours are of the maxima are interpretedas being due to partial drawn at 2.00 and 2.30 for PAM-I, L.70,2.00, and occupancyby volatile species,possibly neutrally 2.30 for PAM-2 andPAM-3. with intervalsof 0.3. The chargedHrO molecules.Swayze & Clark (1990)found numbers on the maps indicate the e value for each several different OH-stretching and OH-bending maximum.Comparison of thesethree figures indicates vibrationsin their IR spectraof carbonate-and sulfate- that there are additional maxima (002) in the large rich scapolites. From spectra taken from oriented TM6 THE CANADIAN MINERAI,OGIST ppm -85 -90 -95 -100 -105 -110 -11F" 2eSi Frc. 3. MAS NIVIR specrra of (a) SyN MA& O) PAM-I, (c) PAM-2, and (d) PAM-3. sections,they determinedthat the speciescausing the additional maxima in our difference-Fouriermaps are peakswere in specificcrystallographic orientations and the first direct information on additional positions for not randomly distributed adsorbed water. They volatile speciesin the scapolitestructure. concludedthat in their samples,OH was related to The 2esi MAS NMR specrraof PAM-I, PAM-2 tlte carbonateor sulfate group. However, they did not and PAM-3 each consist of six peaks, at -92.3, haveany samplesas Cl-rich as the marialite specimens -95.8, -98.7, -102.0, -105.8, -110.7 t 0.1 ppm from Pamir or discussthe possibility of neutral water (Figs. 3 b, c, d). The relative intensitiesof the six peaks moleculesin thechannel above or belowtheA site.The vary for each spectrum.The relative amountsof the STRUCTURALASPECTS OF MARIALITE t047 l]. or, *n NMRspecfium or rot-i-rl* .ix peaksfitted by theleast-squares ;; process;the experimental spectrum, fitted peaks and envelope, and the difference between fittedand experimental slrectra are shown. atoms, in the specific environmentsrelating to each As Al increasesfrom 3.12to 3.24 apfuftomPAM-l sile, were calculatedby fitting the spectrato the sums to PAM-3, there is an increase in the intensity of of peaks, which had a combination of Gaussianand the ?2(1Si3Al) and 71(3SilAl) peak, at -92.3 and lorentzian line shapes(Frg. 4). The areasunder the -105.8 ppm, relativeto the peaksdue to f2(2si2Ai), fit0edpeaks were convertedto relative intensitiesand Z2(3Si1Al), T2(4Si), and Zl(4Si) sites,as expected related to the number ofSi apfu contributing to each (Table 6). There are 4.00 Si apfu n the 11 sitesfor all peak (Table 6). The elror on the measurementof threesamples, within experimentalerror, conoborating relative intensity was found to bet2Vo fromthe specha that the single peakin each27Al spectrum is due to Al of PAM-I obtained at differing values of relaxation n the TZ site, andthat therels nq significant amountOf delays.The 2esiMAS NMR spectrumof the synthetic Al in the 71 site. marialitehad a very poor signal-to-noiseratio (Fig. 3a); however,it can be seenthat peakssimilar to those of the natural samplesare present. The signal-to-noise ratio ofthis spectrumwas consideredto be too low to allow a msnningful integration of the peaks or for it TABLE 6. @--ITYE I'TTF.ISTTBS FOR,gsi MAS NMR SPECTRA to be worth undertakingthe laboriousfitting procedure on the 27Al center band and sidebandsof satellite PeL poafdoa hak 8lloc€i@ PAM-I transitions. aod all@dono Previouswork has shownthat wherethe Si:Al ratio -92.3w I2{ISi3AD 16%(r,4) r5%(r3) 17%(rs) peaks in 2eSi -95.8ppo T2(25,12lJ,) 14%(1.3) u% 0a 14%(r2) becomes2:1, there are only two the -rE7 plu I2(3Si,1Al) Be $2) r47o(12) 13%(1,1) spectrum,at -92.3 and -105.8 ppm, due to the two -ro2-op!@ r2({sD 12%(r,o) 12%{r.r) rrEo0n) Si environmentsof I3(3Al lSi) and n(lAf 3Si) Total fq f 2 55&(4,9) 55%(4.8) 55%GA) (Sheniff et al. 1987). Allowing for a shift of about -16€pln I(3Sl,1Al) MQA 3M(L7) WoW 4 ppm to high field for each substitution of a -u0.7 !!o r (4Si) 15%(r.4) 15%(\s) ts%(rs) peaks 2esi neighboringAl for Si, the six in the spectra TdlfoIl $%@,4 45%(4.0) 45%(4,0) of the marialitesamples ar-92.3, -95.8, -98.7, -102.0, 1m%(8.9) l@, (8.8) l@% (&E) -105.8, -110.7 ppm were allocatedto ?2(1si3A1), TffiI 71(3Si1Al) and T2(2Si2Ar), r2(3Si1A1), T2(4Si), numbd ol Si mm p€r lomula mit itr p@!ths, 71(4Si), respectively. at rcf6 b emhedol siB @neiniag eitlq si 6 Al. 1048 TIIE CANADIAN MINERALOGIST -100ppml -200 FIc. 5. 27Alsatellite transition spectra of PAM-I showingthe experimental(solid line) and fitted (dashedline) central transition (CT) and satellite transition (ST) line-shape, and the experimentaland simulatedsideband envelope. 27Al The spectrafor the three natural sampleshave It would be expectedfrom the Al avoidancerule a similar single center band and satellite transition (Lowenstein1954) that whereA1 is sufftciently dilute sideband peaks. The isotropic chemical shift of in the system, there will be no AI-O-A1 bonds. 58.7 ppm, quadrupolarcoupling constantCo of Therefore,only (4Si) sites should be presentin these 1.98MHz and asymmetryparameter n of 0.8 to 1.0 compositions of scapolite. However, if the total werecalculated by fitting the shapeofthe centerband number of Al atoms is calculated from the relative and sidebandand the sidebandenvelope (Fig. 5) using intensities of the peaks fitted to each 2eSispectrum 350 Hz Gaussianline broadening.A1 appearsto be in using the formula: a single 72 environment in the three samples, in agreementwith the I-O bond distancescalculated Al=1a(ml4)Iq.^ from the Rietveld refinementsand with the 2esi MAS NMR spectra. However, there is a distribution in Bngelhardt & Michel (1987) and referencesthereinl, the quadrupolar coupling constant of 85 kHz, the results for PAM-I, PAM-2 and PAM-3 are 2.6, indicating someslight variation in environmentamong 2.6 and2.7,respectively, instead of the expectedvalues Al sites. of 3.1, 3.2, and3.2. This translatesinto 3.4. 3.2 and STRUCTURALASPECTS OF MARIALITE tu9 3.3 Al-O-Si bonds per Al atom instead of the 4 that 4. nAl satellitetransition and 2esiMAS NMR spectra would be expected.Either there is less Al in the unit show that Al is located only in the Z2 site. There is a cell than has been calculated from the electron- strong indication that A1-O-AI bonds are present microprobeanalyses, or up to 807oof the Al atomsare betweenmost of the Al atomsin thesecompositions of involved in one AI-O-A1 bond. in violation of scapolite,in contraventionof Lowenstein'srule, but in Lowenstein'srule. agreementwith the calculationsof Tossell (1993). Tossell (i993) calculated that the difference in energybetween paired and alternatingSi and Al atoms AcrNowleocEl'{El.lrs in a four-memberedring of Si2Al2Ot2Hs2-is only 63 kJ/mol rather than the previously calculatedvalues Sampleswere kindly provided by S. Sergeevand of >400 kJ/mol (Hasset al. 1981.,Sauer & Engelhardt F. Rafikova. Researchexpenses were supportedby a 1982,Nawotsky et al. 1985,Derouane et al. 1990, RussianFund for Basic Researchgrant 95-{5-15699 Pelmenschikovet al. 1992). This value is further to E.V.S. and Y.K.K., a Natural Sciences and reducedby about22 kJ/mol by the addition of a single Engineering ResearchCouncil University Research Na cation to the atom ofbri.lgrng oxygen,as is present Fellowshipand Research Grant to B.L.S., and National in the structureof marialitic scapolite.This 40 kJ/mol ScienceFoundation Grant EAR-9316W9 to D.M.J. result is consistent with the calorimetric data of Specialthanks are given to David A. Vanko for advice Nawotskyet al. (L982,1985) and the studyof lattice- on the synthesisof marialite. We thank Jian-jie Liang, energy minimization(Bell et al. 1,992).With these an anonymousreferee and AssociateEditor Peter B. small differences in energy, either of the two Leavensand Robert F. Martin for helpful commentson configurationsis possible.Therefore, we suggestthat this manuscript. the single 2741peak in the marialite samplesoriginates from the Z2(3SilA1) environment.The lack of a small REInnsNCEs 27Alpeak expected from the fl(4Si) may be dueto the lack ofresolutionofthe (4S0and (lAl3Si) peaksunder AnrrN,8.G.,EvANs, H.T., JR. & Kotnrranr,J.A. (1984): The the broad centerand sidebandpeaks, but also may be crystalsffucture of a syntheticmeionite. Neues Jahrb. the cause of the distribution of the quadrupolar Mineral.Abh. 149, 309-342. coupling constant. R.G.,JAcKsoN, R.A. & Ceuow, C.R.A.(1992): point, BELL, A1 this there is no evidenceas to whetherthe l,owenstein'srule in zeoliteA: a computationalstudv. A1-O-AI bondsare within or betweenthe 4-membered kolites 12,870-871. T2 rings. The distancefrom Na to -O(4), betweenthe 4-memberedrings, is 2.9 to 3.0 A, whereaswithin BELoKoNEVA,E.L., SoKoLovA, N.V. & DoRoKHovA,G.I. the 4-memberedrings, the distancefrom Na to O(2) (1991):Crystal sffucture of naturalN4Ca-scapolite - an is 2.4 A, and to O(3), it is 2.6 A. Therefore,the intermediatemember of the marialite-meioniteseries. Sov. stabilizing influence would be greater within Phys.Crystallogr. 36, 828-830. the fow-memberedrings, wherethe Na-O bond is the (1993): - shortest.We interpret thesedata to indicate that there & Unusov, V.S. Scapolites crystalline structuresof marialite (Mell) and meionite are Al-O-Al bonds within the four-membercd T2 (Me88) - space group as a function of composition. rings. Crystallogr. Rep. 38(1), 25-28 (translated from Kristallogr. 38, 52-77 ). CoNcLustoNs BSRAR,J.-F. & Lrnmt, P. (1991):E.S.D's and estimated 1. Rietveld refinementfrom X-ray powder data of the probableerror obtainedin Rietveldrefinements v/ith local marialite samplesfrom the Pamir Mountains confirm conelations.J. Appl. Cryxallogr.24, l-5. tetragonal symmetry describedby space group l4lm. (1990): There is a linear trend in the cell parametersfrom the CoMoDr,P., Mum,u, M. &Zxezzt, P.F. Scapolites: variation of structurewith pressureand possible role in the synthetic marialite end-memberthrough the natural storageof fluids. Eur. J. Mirrcral. 2, 195-202. samples(Mea.6, Me7.5 and Mez.o). 2. Our structuralrefinement of Mea.6@AM-l) is the DERoUANE,E.G., Frupnr, J.G. & Baurtoos, R. (1990): closest so far to the natural marialite end-member. Quantum mechanical calculations on molecular sieves. The syntheticMa end-memberhasunifcell pammeters II. Model cluster investigation of silicoalumino- a 12.0396.(2)A, c 7.54/7(2) A, with V equal to phosphates.J. Phys.Ch.en.94, 1687-1'692. 1093.3(4)A3. 3. Additional electron-density maxima on the DoNNAy,G., SHAw,C.F., m, Buu-sR,I.S. & O'Nen, J.R. (1978): The presenceof HCI in scapolites.Can. Mineral, difference Fourier mapsindicate that there are volatile 16.341-345. species,probably neutral HrO molecules, in the intersticesabove and below the A site in the structure DUNN,P.J., NneN, J.E. & NoRBERc,J. (1978): On the of marialite. compositionof gem scapolites.J. Gemmol.16,4-10. 1050 T}IE CANADIAN MINERALOGIST ENGHfiARDT,G. & Mrcru, D. (1987):HiSh ResolutionSoli.d Psr-MEr,rscHrKov,A.G., PAItKsrms, E.A., Eotsnnnasnvnq StateNMR of Silicatesanl T*olites. JohnWiley and Sons, M.O. & Znnounov, G.M. (1992):On the lowenstein's New York" N.Y. rule and mechanismof zeolite dealumination.J, Phys, Chem.96,7051-7055. HAss, E.C., MEay, P.c. & Pmm, P.J. (1981): A non- empirical moleculm orbital study on Lowenstein's rule Poucuou, J.L. & Hcrror& F. (1985) '?AP- (phi-rho-Z) and zeolitecomposition. J. Molecular Struct.76, 389-399, procedure for impmved quantitative microanalysis. 1n MicrobeamAnalysis (J.T. Armstrong,ed.). SanFrancisco Hassal, I. & Busncr, P.R. (1988):HRTEM characterization hess, SanFrancisco, California (104-106). of scapolitesolid solutions.Am. Mineral.73, 119-134. Saunn,J. & ENcnunror, G. (1982):Relative stability of Htrr, R.G. & FLAcK,H.D. (1987):The use of the Durbin- A1-O-A1 linkagesin zeolites.A non empirical molecular Watson d statistic in Rietveld analysis. J. AppI. orbital study.Z. Natur. 37L, 277-279. Cry stallo gr. 20, 356-36'1. Scnnnnn, J. (1989): Profile refinement on IBM-PC's. JoHeNNss,W. (1978): Pressurecomparing experiments with I.U.Cr. Int. Worl PERAUDEAU,G., McMul-eN, P. & Cotm:nrx, J.-P. - (1973b): Structuralrefinement of the Monte Somma (1982): A thermochemicalstudy of glassesand crystals scapolite, a 93Vo meionte. Schweiz.Mineral. Petrogr. along the joins siJica - calcium aluminate and silica- Mitt. 53,385-393. sodium aluminate. Geochim. Cosmochim.Acta 46. 2039-2047. ZoLorAREv,A.A. (1993): Gem scapolite from the eastern Pamirs and some general constitutional features of PApuG,J.J. & Srwnmsolq, N.C. (1966):The crystal srrucrwe scapolites.7ap. Vses.Mineral. Obshchzst.lX\90-L02. ofmizzonite, a calcium-and carbonate-richscapokte. Am. Mincral. 51, 101,4-1027. & Zat'rN, T. (1965): The crystal srrucure of a ReceivedApril 15, 1996, revised manuscript accepted marialite scapolite.Atn. Mineral. 50, @1-655. JUI''r18. 1996.