69
The CanadianMineralo gist Vol. 32,pp. 69-80(1994)
MAS AND DORNMR STUDY OF AI.Si ORDER IN THEANALCIME-POLLUCITE SERIES
DAVID K. TEERTSTRA.BARBARA L. SHERRIFF,ZHI XU AMOPETR CERI\r.i Departmentof GeologicalSciences, University of Manitoba,Winnipeg, Manitoba R3T 2N2
ABsrRAcr
Al-Si order in the analcime- pollucite series(ideally NaAlSi2O6.H2O- CsAlSirO6)was studiedusing magic angle spinning(MAS) and doublerotation (DOR) nuclearmagneti" reronunce (tttr,m.). fne 27AI-2eSi,3Na and ll3CsNMR spectra ofnatural and synthetic samplesshow signs ofincreasing disorderfrom analcimeto pollucite, but the syntheticphases may contain up to about 50 mol.Vopollucite without a significant increasein disordercompared to end-memberanalcime. Cubic pollqcite is the most disordered;however, completedisorder is not observe4 even in rapidly formed, syntheticend-member pollucite. In the cubic framework, cations are not randomly distributed amongtetrahedmlly coordinated sites, but follow an Al-O-Al avoidancerule and probably also the extendedl,oewenstein rule. Analcime and cesiananalcime show an increased degreeof order with symmetry less than cubic, but remain incompletely ordered.The influence of Si/Al ratio on degreeof order was demonstrated;with increasingSi/Al, intensity shifts in the 2esi spectrafrom the S(3Al) and Si(2Al) peaksto ttre Si(lAl) peak.
Keywords:analcime, pollucite, leucite, cesium,nuclear magnetic resonance, Al-Si order,zeolites.
SoMMeRs
Nous avonsdtudid le degr6d'ordre des atomesAl et Si dansles compositionsde la s6rie analcime- pollucite (en th6orie, NaAtSi2O6.H2O- CsAlSi2O) en utilisant la r6sonancemagn6tique nucldaire avec spinningd l'angle magiqueet avecrotation double.Les spectresdes atomes 2741, 2esi, 23Na et 133Csd'6chantillons naturels et synth6tiquest6moignent d'une augmentation du d6sordreen allant du p61eanalcime vers le pdle pollucite. Par contre,les prdparationssynth6tiques peuvent contenirjusqu'i environ 507o(base molaire) de pollucite sansperie importantedu degr6 d'ordre qui caract6risel'analcime pure. La pollucite cubiqueest la plus d6sordonn6e,sans porr autantAtre complbtement d6sordonn6e, m6me dans des cas de croissancerapide de cristaux synth6tiquesayant la compositionid6ale. Dans 1afame cubique,les cationsAl et Si ne sont pas distribu6sde fagon al6atoireparmi les sites, mais seraientplutdt r6gis par la rdgle voulant que les liaisons A1-O-AI ne sont pas favorisdes,et probablemenlaussi par la Ggle g6n6ralisdede Loewenstein.Analcime et analcimec6sique font preuved'un degr6d'ordre plus 6lev6, avec une symdtrie inf6rieure I cubique,mais ceux-ci demeurentincomplbtement ordonn6es. Nous documentonsaussi f influence exerc6epar le rapport SilAl sur le degr6 d'ordre; ! mesureque Si/Al augmente,f intensitd des pics Si(3A1) et S(2Al) du spectrede 2eSidiminue, tandis que l'intensitd du pic Si(lAl) augmente. (Traduit par la R6daction)
Mots-cl6s:analcime, pollucite, leucite, c6sium,r6sonance magn6tique nucl6aire, degr6 d'ordre Al-Si, z6olites.
Ixrxouucrrou topic of recentNMR studies(Lippmaa et al. 1981, Murdoch et al. 1988,Phillips et al. L989,Kohn et al. Members of the analcime- pollucite seriesare of l99l). However,the Cs-enrichedmembers have not petrogeneticinterest as indicatorsof advancedfrac- beeninvestigated, and are a part of the presentstudy. iionation in rare-elementgranitic pegmatites(dernf The MAS NMR spectrumof tetragonalleucite 1974,1992).They are importantas naturalanalogues (Phillips et al. 1989,Palmer et al. L989)suggests a of syntheticphases involved in long-termconrrinment lower degreeof Al-Si order than in analcime,with of 135Csand 137Csnuclear waste (eernf 1979,Taylor tetragonalor higher symmetry (Murdoch et al. 1988, et al. 1989,Teertstra & Cernf 1992).The degreeof Yoder & Weir 1960).In contrast,X-ray single-crystal Al-Si order in structurallyrelated synthetic phases and refinementsof the structure of leucite have not indi- isomorphousminerals (particularly leucite) has beena catedany long-rangeA1-Si order @Iazzi et al. L976).
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Completedisorder is expectedin the isotropic phases metriesof tetragonaland orthorhombicanalcime arise (suchas pollucite),as randomoccupancy of the 48g from varlable ordering of Al into crystallographically tetrahedral sites is a requirement of cobib (Ia3d) distinct tetrahedral sites, and from the related occu- symmetry. The degreeof Al-Si order in the anal- panciesof the nearestNa site. However, in an X-ray- cime-wairakite serieshas not been studiedbv NMR. diffraction and neutron-diffractionstructure refine- but X-ray structurerefinements of monoclinic mentof monoclinicanalcime, Pechar (1988) claimed a wairakite indicate completeorder of Al and Si disordered(Al,Si) distribution. (Tak6uchiet al. 1919).Here, we investigatethe vari- An additional influence on degreeof order may be able degreeof Al-Si order in analcimeand pollucite, variability in the Si/Al ratio, more typical of analcime and the influence of Na-Cs substitutionin inter- (Edgar 1984),pollucite (Cem! 1974)and ammonio- mediatemembers. leucite (Hori et al. 1986)than leucite or wairakite. One reasonthat SVAI ratios are variableis becausethe Crystal chemistryand structure tetrahedral489 sites are topologically equivalent. Si/Al ratios near 2.0 are probably thermodynamically The aluminosilicateframework of analcime the most stable(Khundadze et al. L970.Senderov & (NaAlSirOu.H2O)is sharedby wairakite (Cao., Khitarov I 971 ). (Cs,Na)1.5Alt.5Sil.5O6was recently A1Si2O6.H2O),leucite (KAlSi2O6),ammonioleucite synthesizedwith a Si/Al ratio of 1.0 and a fully (NH4A1Si2O6)and pollucite(CsAlSi2Ou), and is simi- orderedanalcime-type framework Qinnntlevic et al. lar to that in other, rarer minerals (GaL\ et al. 1978). 1991).Si/Al ratiosof syntheticanalcime vary from 1.5 Two cation sites are availablein the anionic frame- to 10 or more dependingon the Si/Al ratio of the work: a 6-coordinatedcavity aroundthe 24c equipoint materialfrom which it crystallized(Saha 1961, Haaker containssmall cations such as Na+ or Ca2+.and an et al. 1985).If Si/Al is equalto 2.0, Al fills 16 out of irregular l2-coordinatedcavity aroundthe 16b equi- the 489 sites in a unit cell basedon 96 atomsof oxy- point containslarger cations such as K+, Cs+or NHf,, gen. In analcime,the 16 charge-balancingNa+ atoms as well as molecularHrO @eger1969). Wide ranges may be distributed among24c sites. If Si/Al exceeds of chemistryare found amongsynthetic phases that 2.0, Al fills lessthan 16 of the 489 sites.In this case, are isomorphouswith analcimeand leucite (Bayer in pollucite the charge-balancingCs+ atoms have some 1973,Torres-Martinez & West 1989).Considering choice amongthe L6b sites,which leadsto a potential these minerals as a group, we may study the various for ordering. influences, such as crystal chemistry or thermal his- tory, on degreeof Al-Si order and the relationshipsto Er
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Pollucite from near Norway, Maine (sample SiKcl) and pollucite (CsZcr).Minor elementswere PA-O31; University of ManitobaM-47) is gemmy, determinedusing 15 kV, 10 nA, a beamsize of 20 Fm clear and colourless,and isotropic. The material used and count times of 50 s. Standardswere the s:lme as in this study is alrnostcompletely homogeneous, with those for the determinationof minor elementsin the exceptionof rare thin (< 10 pm) veinletsof Cs-rich pollucite. pollucite t quartz.The veinletscomprise less than 17o Resultsof the analyseswere recalculatedto atomic of the material used and should not influence the contentson the basisof six atomsof oxygenper anhy- NMR results. drousformula unit (atomsp.f.u.). The CRK index was calculatedas 100(Cs+ Rb + K)/X cations(Cernf Syntheticsamples 1974), wherc X cationsrepresents the sum of concen- trations of Na + Ca + Mg + Cs + Rb + K. The CRK Syntheticsamples were crystallizedhydrothermally index is basedon assignmentof Cs, Rb and K to the from aluminosilicategel in Teflon-lined Parr bombsat larger L6b site, and Na, Ca and Mg to the smaller24c 200'C with autogenouspressure for 100 hours. sitein Beger's(1969) model of the crystalstructure of Known amountsof anhydroussodium metasilicate and pollucite. aluminumtrichloride hexahydratewere dissolved separatelyin the minimum requiredquantities of NMRmeasurements distilled water at room temperature.The aluminum- bearing solution was rinsed into the sodium meta- Magic-angle-spinningnuclear magnetic resonance silicate solution with rapid stirring. The pH was (MAS NMR) spectrawere obtainedusing a Doty lowered with 1.0 N HCI to a pH between7 to 8 to high-speedMAS probe with a Bruker AMX-500 allow the aluminosilicatesolution to gel. The gel was multinuclearFourier Transform spectrometerconsoleo then rinsed to remove excesssodium chloride and with two magnetsoperating at 8.4 and 11.7Tesla. The filtered to removeexcess water. CsCl was addedto sarnpleswere spunat approximately8 kHz at an angle obtain a specific Na/Cs ratio in the gel, and 1.0 N of 54.7oto the magneticfield. 2eSiMAS NMR spectra NaOH or CsOH was addedto raise the pH to 12. The were recordedat a frequency of 99.3 MHz with pH was also measuredafter crystallization, again at 8190 data points, a spectralwidth of 50 kHz, room temperature.The resultant subsphericalcrystals 30opulses and delay of 5 to 30 s betweenpulses. 27Al are optically isotropic, clear and colourless,and up to and23Na spectra'were recorded at frequenciesof 130.3 30 pm in diameter.The yields are greater than 95Vo. and 132.3MHz at Ll.1 T. and 93.8 afi 95.2MHz at The productswere verified to be single-phaseby opti- 8.4 T, respectively,with a spectralwidth of 50 kHz, cal microscopy, X-ray powder diffraction and EMP 10opulses and a delay of 0.1 s betweenpulses. analysis. l33csMAS NMR spectrawere recordedat a frequency of 65.6 MHz at 11.7T with 2000 datapoints, 1.0 trrs Analysisof samples pulsesand a delay of 0.5 s betweenpulses. Peak positions were measured with reference to Polishedthin sectionsof the sampleswere analyzed tetramethylsilane(TMS) for 2esi,a I M aqueoussolu- with a CAMEBAX SX-50 electronmicroprobe, using tion of aluminum chloride for 27A1,0.1 M aqueous the .'PAP" data-reductionprocedure of Pouchou& solution of NaCl for 23Na,and 1 M aqueoussolution Pichoir (1985).Back-scattered electron imaging was of CsClfor 133Cs. usedto investigatethe homogeneityof all the samples. The 2esi signal-to-noiseratios of both the natural For pollucite,concentrations of major elements and syntheticsamples are low owing to relatively long were measuredusing 15 kV, 20 nA, a beam size of T, relaxation times. The relative areasof the 2esi 5 pm, and count times of 20 s. The standardsused peaks were found by cutting out and weighing the were pollucite (AlKcl, SiKcr,CsZcr) and albite peaks;this haspreviously beenfound to give as accu- (NaKa). Minor elementswere determinedusing rate valuesfor thesebroad lines as least-squares-fitting 15 kV, 40 nA, a beam size of 5 pm and count times of techniques(Sheriff et al. 1987). 50 s. The standardsused were rubidian microcline Quadrupolarinteractions of nuclei lvith spin geater (RbIo), orthoclase(FeKa, KKa), anorthite (CaKcr), than /2, such as 27Al and 23Na,cause line broadening hornblende (MgKd) and vanadium diphosphate and peak shifts in solid-stateNMR spectra.These can (PKcr). be reducedby double-anglerotation (DOR) NMR For analcime,concentrations of major elements experimentin which an inner rotor spinsat an angleof were measutedusing 15 kV, 10 nA, a beam size of 30.2" to the magneticfield while an outer rotor spins 20 trrm,and count times of 20 s. Analcime interacts at the magic angle of 54.7' (Wu et al. 1990). Tbe with the electron beam more strongly than pollucite; inner rotor averagesout second-orderquadrupolar thus a larger bearn-sizeand lower cunentswere neces- interactions,whereas the outer rotor reducesbroad- sary to prevent loss of counts due to sample volatil- ening due to dipole-dipole interactionsand anisotropy ization. The standardsused were albite (NaKcLAIKcL in chemicalshifts.
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Double-rotationNMR spectrawere obtainedfor Intermediatemembers of the analcime- pollucite 23Naand 27Al using a Bruker DOR probe with the solid solution (SYNAN-OO were found to be hetero- 8.4 T magnet.For both nuclei, a spectralwidth of geneousand growtl,zoned in Na and Cs (Fig. 1A). 25 kLIz, pulse lengthsof 2 ps and a delay between The crystalsare desciibedhere because they are prob- pulsesof 1 s was usedto recordthe spectra.Reference ably analogousto synthetic phasesthat contain standardswere the sune as for the MAS experiments. l35Csand 137Csnuclear wastes. Composition varies Spectrawere observedat differentspeeds of spinning betweencrystals over the interval from CRK 36 to 76. in orderto distinguishpeaks from spinningsidebands Some variation in SVAI ratio with CRK is evident (Xu & Sherriff 1993).A methodof synchronization (Fig. 1B),and is reflectedin a plot of Al (atomsp.f.u.,r was used to eliminateodd-numbered spinning side- versasCRK (Fig. lC). This plot alsogives the sumof bandsand increasesignal-to-noise ralio (Wu et al. cation charges(atoms p.f.u.) versasCRK to indicate 1990). the chargebalance in the analyticalresults.
RFsuLTs Silicon NMR
Analytical results In analcime.the 2esi chemical shifts of individual peaksdepend mainly on the number.ofAl atomsin the Compositionsof the natural and synthetic samples secondcoordination sphere of tetrahedrallycoordi- are given in Table 1. The syntheticcrystals of end- natedSi atoms(Murdoch et al. 1988).Each additional memberanalcime were found to be homogeneous,as Al next-nearestneighbor gives a shift of approxi- was the synthetic end-member pollucite. mately5 ppm to low field (Lippmaaet al. l98l).T\e Unforfunately,only atomic ratios could be determined numberof Al atomsis designatedusing the nomen- for the syntheticpollucite (SYNAN-09) becauseof a clatureSi(4Al), S(3Al), S(2Al), S(1Al), and Si(0A1) grain size too small for quantitativeEMP analysis: for the five possiblenext-nearest neighbor environ- Si/Al = 2.3 + 0.I; CRK = 97 t3.In thebulk sampleof mentsof the tetrahedra.Assignment of tle peaksto SYNAN-{9, isotropiccrystals have a n of 1.522 arrd, specific environmentsof the tetrahedrawas basedon contain0.96 wt.VoH"O. calculationof chemical shift using theoreticalmodels
TABIJE 1. CNEI{ICAL Co!{POSI1rION OF |rITE SlliPLES USED
lldnodanaolts aht-hatl d 16rl d'lma
oxlde pa-1 50 pa-1)) pA-o?1 svNAN-n? svtraN-n4 svtitlN-2?
S1o2 rrt.? 52.89 (.r4, 57.05 (.11) 47.77 (.r4) 57.58 (.1s) s5.36 (.12) 58.34 (.14) A12o3 24.63 (.O5' 20.56 (.10) 16.02 (.05) 20.e6 (.50) 22.26 (tO5'l 20.53 (.15) Fe2O3 0. 00 0. 00 0.00 0.02 0.03 (.01) 0.05 Pz05 0. 00 0. 00 0.33 (.01) 0.00 0. 00 0. 00 Na2O 13.31 (.11) 11.ee.(.11) 1.67 (.01) 12.36 (.7O' 13.08 (.06) 11.58 (.58) K2o 0.73 (.01) o.o2 o.o2 0.o2 o.o2 0.11 Rbzo 0. 00 o.oo"' 0.2e (.01) 0.00 0.00 0.00 C62O 0. 00 1.2e (.05) 32.52 (.2O' 0.00 0.00 0.00 cao o. 02 0. oo o.o2 0.01 o.o2 0.03 Hzo 7.67 7.37 1.70 7.54 '7.45 7.54
Ellll >Y.22 94.24 100.34 98.51 98.63 94.32
s1 2.06 2.TL 2.L4 2.04 2.13 0. 99 0.90 0.86 0.90 n o? 0. 88 Na 0. 98 0.86 0.15 0. 88 c6 o. oo 0. 02 0. 63 0.00 o.00. 0.00 t cbarges 0. 88 0.81 0.88 o.94 o. 83 sllA1 2.O3 2.36 2.44 2.33 2.4L CRK or6 2.4 aI.2 0. 01 o. 0L 0. 08
n 1. 488 I.4A6 1.519 1. 489 1 -4AL 1 A9A Note6: 1) CRK = 100(Cs + Rb + K)/t cations. 2) AtoDlc contents on the basls of 6 atoms of oxygen per anhydrous fornula unl-t. 3) n * Lndex of refraction. l) ( ) = one standaral devlatlon based on 6-10 analyses. 5) See tex! (analtrtlcal resuLts) for detailE . of 6ynth6tlc poLLuclte (SYNAN-o9) and cesian analclme (SYNAN-06).
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A
SYNAN-06 synthetic cesian analcime
2-4 ,.1f B Si/AI I I ,.rl t t! !l lt r I I frr I t I '' ,..[
AI a
SUm Of 0.e5 cation chargeso.no
40 60 80 CRK FIc. l. a) Back-scatteredelectron image of syntheticcesian analcime (SYNAN-06). Brighter areasindicate higher Cs contents.Some grains have a Na-rich core, and a Cs-rich rim. Scalebar: 100 pm. b) Si/Al yersasCRK [= 100*(Cs + Rb + K)/cation suml. c) Al and sum of cation charges(atoms per formula unit) versasCRK. The ana- lytical precisionis t0.02 (Si/Al), 10.01 (A1, and sum of cation charges)and t0.1 (cRK).
for local environmentsof silicon in tectosilicates Peak assignmentsand chemical shifts are given in (Sheriff et al. l99l). Table 2, togetherwith the relative areasunder the The 2esi spectrumof natural analcime(PA-150; peaks.Differences in the spectralie mainly in the rela- Fig. 2A) has a major peak at a chemical shift of tive intensity of the peaks.The greaterintensity of the -96 ppm, and minor peakswith chemical shifts minor peaks of synthetic analcime comparedto of -91 and -101 ppm. The major peakis assignedto the casefor natural analcimeis due to a greater S(2Al), and the minor peaksto S(3Al) and Si(lAl), proportionof Si in the Si(3Al) and Si(lAl) environ- respectively. ments. The spectraof synthetic analcime (SYNAN-03, The 2esi spectrumof natural pollucite (PA-031; 04 and 23; Figs. 28, C), natural cesian anal- Fig. 34) has two major peaks with chemical cime (PA-122), and syntheticcesian analcime shifts (Table2) of -96 and -l0l ppm, assigned (SYNAN-06) are similar to that of natural analcime. to S(2Al) and Si(lAl), respectively.The spectrumof
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IIABLE 2. 29SI. ldAg N![R PANA!{ETERfI
Peak posltion, ppn (relatlve area of peak)
PA-150 -91.3 -96.3 -101.0 (14) (65) (21) PA-L22 -96.9 -101.4 (0) (75) (25) PA-o31 -96.4 -101.4 (0) (6e) (32) SYNAN-o3 -91.1 -96.2 -101.1 (20) (56) (24) SYNAN-o4 -91.3 -96.5 -l-01.7 (23) (51) (26' SYNAN-23 -91.5 -96.4 -101.7 (15) (50) (35) SYNAN-06 -9L.2 -96.5 -101.0 (20) (54) (26, SYNAN-09 -96.7 -100.6 (0) (77) 123)
t |-I-_-____r___-- -80 -gl -100 -ilo ppm
Frc. 2. 2esi MAS NMR specrraof A) birefringent naturalanalcime (PA-l50), B) cubic syntheticanal- cime (SYNAN-03), and C) cubic synthetic analcime (PA-122) with a higher Si/Al ratio than SYNAN-O3.
syntheticpollucite (SYNAN-09; Fig. 38) is similar to that of natural pollucite, but the corresponding peaksare broader.
AlaminumNMR -sI -so -roo -tto The 27Al spectraof all the natural and synthetic ppm samplesconsist of one broadresonance. In the MAS spectrumof natural pollucite, this peak has a position Frc. 3. 2esi MAS NMR spectraof A) cubic natural near 59 ppm, and a peak width at half-height of pollucite (PA-031), and B) cubic synthetic pollucite 550 Hz at 11.7 T (Table 3). There is no significant (SYNAN-.o9).
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IABI/E 3. ?7AI lIAg NIIR PASAIUEIERfI TABLE 4. ?3NA MAg M'R PARAI{ETERS
Peak P6ak lrldtb at Peak lrldth at
a!93_6-s AtD(500 A!d360 AI|D(500 AID(360 A!O(500 A!O(360 -1"2. PA-150 54.7 490 PA-150 o L420 -L2.L -20,6 L220 L920 PA-r22 54.9 57.3 490 620 -8.1 -12.7 PA-031 58.9 550 PA-o31 1960 2430 l3:l 570 SYNAN-03 -rr.7 L640 stNAN-o3 58.8 -L2.3 SYNAN-oA 58.8 550 SYNAN-04 1380 560 SYNAN-23 -11. 3 1590 sYNeN-z3 58.6 -11.6 -20.0 SYNAN-06 58.8 57.7 570 650 SYNAN-06 1590 2340 SYNAI{-o9 59.2 700
shift in peakposition from analcimeto pollucite; how- heightof 2000Hz (Table4, Fig. 5A). The spectrumof ever, the peak width at half-height increasesfrom naturalcesian analcime consists of one broad,asym- analcimeto pollucite, with the syntheticsamples metricalresonance with a peak position of -12 ppm having broaderpeaks. and a width of 1200Hz (Fig. 5B). A 23Naspectrum 27AlDOR spectrashow only one symmetricalpeak could not be obtainedfrom syntheticpollucite (Frg. 4). In naturalpollucite, at spinningrate speedsof (SYNAN-09), as the contentof Na was too low. the outer rotor of 800 Hz, the peak is at 51 ppm with The 23NaDOR spectrumof cesiananalcime a width at half-heightof 410 Hz. (PA-122: Fig. 6) consistsof one peak at the same positionas in the MAS spectra.The DOR peak,how- ever, has an asymmetricalshoulder, which suggests SodiumNMR that it is a combinationof two or more peaks,resulting from different Na environments.This shoulderis The 23NaMAS peak for natural pollucite has a larger in the 23NaDOR spectrumof synthetic cesian chemical shift of -8 ppm and a peak width at half- analcime(SYNAN--06).
I r't.l I t't'r & sppml|0& 20 0 ppm -e0 -e
Frc. 4. 27AI DOR NMR spectrumof natural pollucite Frc. 5. 23NaMAS NMR spectraof A) natural pollucite (PA--031)showing a single, symmetricalpeak. Spinning (PA-031), and B) natural cesiananalcime (PA-I22), sidebandsare marked(s.s.). showingasymmetrical peaks.
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I l'l I I 20 0 ppm -?0 -/t0 -60
Frc. 6. uNa DOR NMR spectrumof natural cesiananalcime (PA-122). Data were col- lectedat a spinningspeed of 800 Hz. The spinningsidebands (s.s.) were identified by their changein peakposition at lower spinningspeeds, whereas the main peak (with a width of 60 Hz) doesnot changein its position (19.3 ppm). The shoulderto the main peakis markedby the arrow. A small peak (A) was found in the sameposition as the referencestandaxd, solid NaCl at 7.0 ppm, but this peakis not due to NaCl inclusions, asthis gem-qualitysample seems to be free of inclusions.
CesiamNMR ronmentto thosein the Si(3Al) and Si(1Al) environ- mentsis greaterin the spectrumof birefringentnatural 133Csspectra were obtainedfor synthetic cesian analcime (PA-150) than in that of cubic synthetic analcime (SYNAN-06) and natural pollucite analcime (SYNAN--03). The difference in degreeof (PA-031). The spectraboth consistof one very order conelatesin this casewitJr the variation in sym- broad, symmetricalresonance with a position near metry. A 2esi NMR spectrumfor analcimefrom 49 x.4ppn Golden,Colorado, reported by Murdoch et al. (L988), is very similar to our spectrumof cubic, synthetic D$cussroN analcime.They used peak simulations and computer calculationsto propose(Al,Si) distributionsamong Theoretically,the 2esi spectrumof a completely three different tetrahedrallycoordinated sites in anal- orderedanalcime with a Si/Al ratio of 2.0 shouldhave cime. However,they did not statewhether their crystal only a single peak, due to the S(2Al) environment.If is birefringenc if cubic, it would have only one tetra- the Si/Al ratio is greater than 2.0, and the structure hedral site, but if monoclinic, it must have six crystal- is still ordered,an additionalSi(lAl) peak should lographic sites. Analcime from the Golden, Colorado appear.With Si/Al ratios less than 2.0, the Si(3Al) locality was describedby Yoder & Weir (1960) as peak shouldbe present.Fully orderedsodian pollucite, being isotropic to slightly birefringent, with a Si/Al with a SVAI ratio of 1.0,has a singleS(4Al) peakat ratioof2.13. -89.6 ppm (Dimitdevic et al. L99l). The 2esi spectrumof natural birefringent analcime Increasingdisorder (at SilAl = 2.0) is indicatedby (PA-150) is similar to the spectrumof naturalbire- the appearanceof Si(0Al), S(3AD and Si(4Al) peaks fringent cesiananalcime (PA-L22), exceptthat the and a correspondingdecrease in the intensity of the latter spectrumlacks the Si(3Al) and has a larger Si(2Al) peak. It may also be correlatedwith an S(1Al) peak. This cesiananalcime is tlerefore more increasein peak widths due to overlappingpeaks from orderedthan the end-memberanalcime, but the higher slightly differing 2eSienvironments. Si/Al ratio gives a larger Si(lAl) peak (Table 2). This The ratio of the number of Si in the Si(2Al) envi- is shown more clearly by the spectra of synthetic
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sampleswith differing Si/Al ratio. An increasein the much more disorderedthan in analcime.Sample relative intensityof the Si(lAl) peak is evidentin a PNI22 has a symmetry lower than tetragonal, and comparison of the spectrum of SYNAN-O3, with should be more orderedthan leucite, yet we see only a low Si/AI ratio (Fig. 2B), to that of SYNAN-23, onepeak, even in DOR experiments. with a higherSi/Al ratio (Fig. 2C). The 23NaMAS spectraof syntheticsamples tend to The similarity of the spectrumof synthetic cesian have broaderpeaks than the natural samplesowing analcime(SYNAN-O6) to that of syntheticanalcime to the higher overall degreeofdisorder. However,the (SYNAN-O3 and SYNAN-O4) showsthat the frame- changein shapeand position of the 23NaMAS peak work of synthetic cesiananalcime is not significantly from analcime to pollucite indicates a changein the 23Na more disorderedthan syntheticend-member analcime. Na environment@gs. 5A, B). The shift in peak _ Both the natural and synthetic pollucite are cubic. position with increasingCs contentwas also visible in Cernf (1979) estimatedthe conditionsof crystal- the DOR spectra.The shoulderto the main peakin the lization of naturalpollucite to be in the rangeof 600 to DOR spectrum,which indicatestwo Na environments, 300'C at 4 to 2 kba\ but suggestedthat in natural B, becomesmore distinct with increasingCs content. F, Li, H2O-rich pegmatite-forminggranitic melts, the Variation in the local symmetryof the Na site doesnot temperatureis most likely 400 to 300'C. Despite seem to be the main factor. as there seemsto be no this higher temperatureof crystallization of natural strong variation betweencrystals of different symme- pollucite, it is more orderedthan the synthetic pollu- try. In single-crystalstructure refinements (XRD), the cite, which crystallized at 200'C (Figs. 3,A.,B). This electron distribution associatedwith the Na site is could be due to a longer period of crystallization and strongly anisotropic,in the direction of the HrO mole- cooling. The higher Cs contentin the syntheticpollu- cules.A changein H2O:Naratio from 2:1 to 1:l from cite may make a significant contribution to disorderin analcimeto pollucite may be the causeof the two 23Na the (Al,Si) framework;however, the pollucite could DOR peakswe observed,if it meansthat someNa also have crystallized metastablyat temperaturestoo atomsare flankedby oneH2O molecule rather than two. low for orderingin tle solid state. The increasein 27Al peak widths from analcimeto Ordering,syrnmetry and composition pollucite indicatesincreasing disorder in the structure with increasingCs content. As the number of Analcime and pollucite belong to the Class4 of Al-O-Al bondsis minimized(Loewenstein 1954), zeolites (Gottardi & Alberti 1985); these are zeolites this must be due to disorderof Al and Si in the tetra- with Si in excessof Al" and a framework that favon hedrally coordinatedsites four bonds away from the disorderbecause the tetrahedrallycoordinated sites are Al. Cesiananalcime (PN-122) is optically biaxial and, topologicallyidentical. Order is definedcrystallo- therefore,has orthorhombicor lower symmetry,which gaphically by a three-dimensional,patterned filling of requiresat leasttbree distinctive crystallographicsites. cation sites. Disorder refers to a random distribution In the DOR spectrumof PN-122, the peak nanows to ofcations, which in the tetrahedralsites favor variable 4I0Hz but doesnot separateinto threepeaks, proba- Si/Al ratios.Si/Al ratios tend to be near2.0 in most bly becausethe thrpe sites have similar environments natural samplesof analcime,although higher Si/Al or becausedisorder is causingsufficient broadening of ralios aretypical of cesiananalcime and pollucite. each peak for them to not be resolvable.The resolu- In syntheticanalci:ne, Khundadze et al. (1970),and tion possiblewith the DOR techniqueis shownby the Senderov& Khitarov (1971) showedthat Si/Al ratios peak width of 43 Hz obtainedfor the 27AlDOR spec- near 2.0 are thermodynamically tle most stable and trum of an extremelywell-ordered sample of tugtupite suggestedthat this constancyof compositionis due to (Xu & Shenitr 1994). (Al,Si) order in the structure. Howeveroorder is not If there is more than one distinct A1 environment li:rked to SilAl ratio, as crystalswith Si/Al of 2.0 may in analcime,we would expectto observethe xJl2 <-> be highly disordered.Based on results of chemical *3/2 satdlite transitionsin the lrst spinningsidebands analyses,Pechar (1988) used an order-disorderpara- of the MAS spectraregardless of the strength of the meter Q = Si/(Si + A1 + Fe3*; to describethe distri- magneticfield (Xu & Sheniff 1993),because the inner bution of atomsin tetrahedrallycoordinated sites and satellite transitions have small secondmoments and incorrectly concludedthat his monoclinic analcimeis sufficient intensity to be observed(Samoson 1985). disordered.This is a requirementof cubic symmetry. In two magneficfields, the sidebandsare broad but Our researchindicates that variable degreesof order clearly without resolutioninto separatepeaks. do not require changesin Si/Al ratio; therefore, this These274.1 results seem to conflict with those of type of parametercannot be used to quantify the Phillips et al. (7989), who reportedthe presence degreeof order. 'ofull of threepeaks in a MAS spectrumof leucite. Only one TI'rcla3d spacegoup requirementof disorder X-ray structure refinement of leucite has been pub- among 48g sites" should be interpreted liberally for lished, as leucite is intenselytwinned. This showed long-range(X-ray and optical) observations.With ran- tetragonalsymmetry and an (Al,Si) frarr'ework that is dom occupancyof Al amongthe 48g sites,we may
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expectAI-O-A1 linkages,which must be avoided of crystal growth, phasetransformations, pre$sure (Loewenstein1954); however,in theseSi-rich miner- conditionsand subsequentthermal history. In ANA als, even AI-O-Si-O-A1 linkages are likely to be crystalswith symmetrylower than cubic, NMR cannot avoidedin line with tJreextended Loewenstein rule distinguish betweencrystallogaphically distinct sites (Merlino 1984).This accountsfor the partial order becausethe siteshave nearly equivalentenvironments found even in rapidly formed syntheticpollucite. ofbonding. However, synthetic analcimehas a greater degree The degreeof disorder increasesfrom analcimeto of order. This situation may be explained by pollucite, but completedisorder was not found. Even the proximity of Na to Al in analcime.The conceptof rapidly synthesizedend-member pollucite is partially local charge-balancein a small area(Pauling's orderedas a result of Al-O-Al avoidance:the secondrule) is probablyvalid during crystal $owth extendedLoewenstein's rule probablyalso is applic- (Akizuki 1981). able, as theseminerals typically are Si-rich, with Si/Al Ordering in these minerals is known to be rather greaterthan 2.0. sluggishafter crystallization(Khundadze et al. 1970). For containmentof nuclear wastesin analcime- Only for synthetic wairakite has re-ordering been related phases,SilAl ratios near2.0 and low levels of demonstratedon an experimentaltime-scale (Liou 135Csand 137Cswaste, with a Cs/Naratio lessthan 1, 1970).In nafural analcime,ordering probably takes are recommendedon the basis of maximum potential place mainly during crystal growth (Akizuki 1981, degreeof order and probablethermodynamic stability. Papezik& Elias 1980).Akizuki (1981)related surface features of analcime crystals to optical symmetry ACKNOWLEDGEN&NTS (isotropicversus uniaxial), and suggestedthat the vari- able symmetryresulted from the degreeof order pro- The authorsthank Brian Sayer of McMaster ducedduring growth on a specific surface-topology.In University for assistancewith NMR instrumentation. this case,the cubic (Ia3d) phaseis requiredto be more Kirk Marat and Terry Wolowiec assistedat the Prairie disordered;in general,we expectthe highestdegree of Regional NMR Center.Acknowledgements to Bruker order in crystalswith the lo\ilest symmetry.However, Spectrospin(Canada) Ltd. for the loan of the DOR lower symme{rycould result from a slight, systematic probe. Thanks to Peter Vanstoneand the Tanco rotation of tle tetrahedraduring growth, which does Mining Corporation,forassistance in samplecol- not involve orderingor even changeduring cooling lecting, and to Iva Cern6for specimensfrom the from a higher-temperahrre,more symmetricalphase. R.B. FergusonMuseum of Mineralogy,University of In natural pollucite, the presenceof the large Cs Manitoba. Funding was provided by an NSERC atom may sterically hinder mechanismsof order; how- University ResearchFellowship and OperatingGrant ever, tlle relatively high temperatureof crystallization to BLS and NSERC Operatingand Major Installation can also be a factor. We have detectedsome degree of grants to PC. Special thanks to R.N. Abbott, R.F. order in isotropic pollucite, suggestingthat even a Martin and two anonymousreviewers for comments highly orderedframework can accommodateCs as the on an earlier draft of this paper, which lead to sub- dominant cation. [n pollucite, symmetrieslower than stantialchanges in the presentmanuscript. cubic may be due to ordering alone,as the framework requires little adjustmentto fit ttre size of Cs+ (Roth et al. L991.).A weak, loca1birefringence has been RSFERENCES reportedin natral pollucite but, to date, tlere are no publishedrefinements of the noncubicstructure. AKzuKr, M. (1981): Origin of optical variation in analcime. Am. M ineral. 66. 403-409. CoNct-ustotts Ar-rnnrr, A. (1991): Crystal chemistry of Si-Al distribution We have observedonly intermediateand variable in naturalzeolites. Stud. Surf. Sci.Catalysis 60, L07-122. degreesof order, in agreementwith the findings of Gottardi& Alberti (1985);we have not found states Bawn, G. (1973):Thermal expansion of new leucite-type 6f gem.lleteorder or completedisorder, in agreement compounds.Narurwiss. 60, 102-103. with the fildings of Alberti (1991)in other zeolites. We concludethat there are no sirnple relationships BEGER,R.M. (1969):The crystal structureand chemicalcom- position of pollucite. Z. Kristallogr. 129, 280-302. betweenstates of Al-Si order and symmetry in anal- cime and related ANA minerals"because of variable CeRNf, P. (1972): The Tanco pegmatiteat Bernic Lake, influences of composition,growth mechanisms, ther- Manitoba.\{tr. Secondaryminerals from the spodumene mal history and displacivephase-transformations. The rich zones.Can. Mineral. 11. 7 1,4-726. degreeof order dependsmainly on the type of inter- framework cation present,with a lesser influence of - (1974): The present statusof the analcime-pollucite variableSi/Al ratios in the framework.mechanisms seies. Can.M ineral. 12. 33+34I.
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- (1979):Pollucite and is alterationin geologicaloccur- Lrppuaa, E., MAGr,M., Sauoson, A., TARMAK,M. & rencesand in deep-burialradioactive waste disposal..lz ENcBlnanor, G. (1981): Investigationof the stucture of Scientific Basis for Nuclear Waste ManagementI (G.J. zeolitesby solid-statehigh-resolution 2esi NMR spec- McCarthy,ed.). Plenum Publ. Co.. New York(231-236). troscopy,J. Am. Chem.Soc. I03,49924996.
- (1992): Geochemicaland petrogeneticfeatures of MAzzt, F. & Gallr, E. (1978):Is eachanalcime different? mineralizationin rare-elementgranitic pegmatitesin the Am.M i neral. 63, 448-460. light of cunentresearch. Appl, Geochcm.7,393416. & GorrARDI,G. (1976): The crystal structure Drurrrumrc, R., Donou& V. & PErRANovrc,N. (1991):The of tetragonalleucite. AnL Mineral.6l, 108-115. high temperaturesynthesis of CsAlSiOn-ANA, a new polymorph in the systemCs2O-A12O3-SiO2. I. The end- MeRLbro,S. (1984):Recent results in sructural studiesof memberof ANA type of zeolite framework.J. Solid State zeolites a.ndzeolite-like materials. Inhoc.6th Int. Conf. Chem.95. 335-345. Zeolites(A. Bisio & D.H. Olson,eds.). Butterworth, Guildford, U.K. (747 -7 59). Eocar, A.D. (1984): Chemistry,occurence and paragenesis of feldspathoids: a review. 1z Feldspars and MuRDocH,J.B., Srusnnqs,J.F., Cewncuanr,, I.S.E. & PtrIFs, Feldspathoids.Structures, Properties and Occurrences A. (1988):A silicon-29nuclear magnetic resonance study (W.L. Brown, ed.).NATO ASISeries 137,501-532. of silicon-aluminum ordering in leucite and analcite. Phy s. Chem Mineral s 15, 370-382. GALLI,E., Gorraror, G. &M"tozr, F. (1978):The naturaland syntheticphases with the leucite framework.Mineral. PALMER,D.C., SauB, E.K.H. & Scls4AHL,W.W. (1989): Petrogr.Acta 22, I 85-l 93. Phasetransitions in leucite: X-ray diffraction studies. Phys. Chem.Minerals 16, 7 l+7 19. Gor"rARDI,G. & Alnnnrr, A. (1985): Silicon aluminium ordering in the framework of zeolites.BulI. Comm. 96ol. V.S. & Euas, P. (1980):Tetragonal analcime from Finl.ande57.197-206. PApEa! southeasternNewfoundland. Can. Mineral. 18, 73-75. Haarnn, R., Malow, G. & Orrmuerx, P. (1985):The effect ofphase formation on glass leaching.In Scientific Basis PEAcoR,D.R. (1968):A high temperaturesingle crystal (K,Na)AlSi2O6. for Nuclear Waste ManagementVII (C.M. Jantzen, diffractometer study of leucite, Z. J.A. Stone& R.C. Ewing, eds.).M.R.S., Pittsburgh, Krista ll ogr. 127,21 3-224. Pennsylvania( 12l -L28). PncueR,F. (1988):The crystal structureof naturalmonoclinic HAaN, R.M. & Fnqcrn,L.W. (1979):Polyhedral tilting: a analcime0.[aAlSizO6.H2O). Z Kristallogr. 1.8/,,$-69. common type of pure displacivephase ftansition and its relationshipto analcite at high pressure.P&asa Psnr,ps,8.L., Knrparx.rcK,R.J. & PrrrNs,A. (1989):Si,Al 27Al Transitions1.7-22. orderingin leuciteby high-resolution MAS NMR spectroscopy.Pltys. Chem. Minerals 16, 591-598. lIRAo, K., Soca,N. & Kuxucr, M. (1976):Thermal expan- sion and structure of leucite-type compounds.J. Phys. Poucrou, J.L. & PIcsorn,F. (1985):"PAP" (phi-rho-Z) Chem.80.1612-1616. procedurefor improved quantitativemicroanalysis. /z MicrobeamAnalysis (J.T. Armstrong,ed.). SanFrancisco HoRI,H., NAcASHTMA,K., Yerr,Iane,M., MryAwAKr,R. & hess, SanFrancisco, Califomia (104-106). Memrsasm, T. (1986): Ammonioleucite, a new mineral from Tatarazawa,Fujioka lapan.Atn. Mineral. Tl,1022- Ronr, R.S.,Bnecr, F. & San-rono,A. (1991):Neutron pow- 1027. der ditraction study of the structuresof the alkali metal alumina silicates,leucite-pollucite. Geol. Soc.Am., Kuuxoepzp, A.G., SnNoenov,E.E. & Knrrenov, N.I. ProgramAbstr. 23, Mlg. (1970): Experimentaldata on compositionof synthetic analcimes.Geochem. 5. 588-600. SaHa,P. (1961):The systemNaAlSiOa (nepheline) - NaAlSi3O8(albite) - H2O.Am. Mineral.46, 859-884. Koun, S.C, Dwn$, R., MoRTUZA,M.G. & HENDERSoN, C.M.B. (1991):An NMR studyof structueand ordering SAMosoN,A. ( I 985): Satellitetransition high-resolution in syntheticK2MgSi5O12, a leucite analogue.Phys. Chem. NMR of quadrupolarnuclei in powders. Chem.Phys. MineralslS.lM-152. Iztters 119.29-32.
LoswENsrEN,W. (1954): The distribution of aluminum in SENDERoV,E.E. & KHIrARov,N.I. (1971):Synthesis of the tetrahedraof silicates and aluminates.Am Mineral. thermodynamicallystable zeolites in the NarO- 39,92-96. AI2O3-SiO2-H2Osystem. Adv. Chem.Ser. l0l,149-153.
Ltou, J.G. (1970): Synthesisand stability relations of Srmnnnr,8.L., GRtrrlDy,H.D. & HenruteN,J.S. (1991): The 2esi wafuakite,CaAJ2S|4O o.2H2O. Contrib. Mineral. Petrol. relationshipbetween MAS NMR chemical shift and n.259-282. silicatemineral structure. Ear. J. Mineral.3,75l-768,
Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/32/1/69/3435657/69.pdf by guest on 26 September 2021 80 TIIE CANADTAN MINERAIOGIST
& - (1987):Occupancy of T sitesin the ToRRES-MARrINEZ,L.M. & WBsr, A.R. (1989): Pollucite- scapoliteseries: a multinuclearNMR study using magic- and leucite-relatedphases: A2BXsOnand ACX2O6. Z. anglespinning. Can. M ineral. 25,7 17 -7 30. anorg. allg. Chem. 573, 223-230.
TAKEucItr,Y.,Mtzzr, F., HAoA,N. & Gellr, E. (1979):The Wu, Y., SuN,B.Q., Pn{Es,A., S.c[4osol,,l,A. & Lrppuaa,E. crystal structureof wairakite.Ara Mineral. 64,993-1001. (1990):NMR experimentswith a new doublerotor. J. Magn. Res.89,297-309. TAyLoR,D. & HENDERSoN,C.M.B. (1968):The thermal expansion leucite group of the of minerals.Am. Mineral. Yonrn, H.S. & Wrn, C.E. (1960):High-pressure form of 53.1476-1489. analciteald free energychange with pressue of analcite reactions.Ar?,. J. Sci. 258-4. 420-433. TAyLoR,P., DnVaar, S.D. & OWEN,D.G. (1989):Stability relationshipsbetween solid cesiumaluminosilicates in (1993):27.{1 aqueoussolutions at200oC. Can. J. Chem-67,76-81. Xv,Zur & SHERRTFF,B.L. double-rotationNMR study of Al2SiO5polymorph minerals.Appl. Mag. Trenrsrna,D.K. & esnNi, P. (1992):Controls on morpholo- ResorLance4.203-212. gy of analcime- pollucite in natural minerals,synthetic 27A1,eBe 2eSi phasesand nuclearwaste products. C4yslal. Res. Technol. - & - (1994):23Na, and NMR study 27.933-94r. of tugtupite.Can. Mineral. 32, (in press).
& CHAIMAN,R. (1992):Compositional hetero- geneity of pollucite from High Grade Dyke, Maskwa ReceivedSeptember 12, 1991, revised manuscript accepted Lake, southeasternManitoba. Can. Mineral. 30,687-697. Mav 20. 1993.
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