609

Thz CanadianMineralo gist Vol. 33, pp.609-626(1995)

THEINFRARED SPECTROSCOPY OF VESUVIANITE IN THEOH REGION LEEA. GROAT Departrnentof GeolngicalSciences, University of BritishColumbie, Vancotner, British Columbia V6T 124 FRANK C. HAWTHORNE Departtnentof GeologicalSciences, University of ManitobaWinnipeg, Manitoba R3T 2N2 GEORGER.ROSSMAN Divisionof Geologicaland Planetary Sciences, Califomia Instinte of Teclnnl,ogy,Pasadena" Califurnia 91125, U.SA. T. SCOTI ERCIT Cannlian Museum of Nature, Mineral Sciences Section, Oxawa. Ontario KIP 6P4

ABsrRAsr Many imFortantsubstitutions in vesuvianiteinvolve variableH, and thosethat do not still perturbthe local environmentof the OH- anions.Consequently, spectroscopyof the OH fundamentaland overtoneregions is an importantprobe of local order.We haveexamined a seriesof vesuvianitecrystals carefully characterized(by electron-microprobeanalysis, wet-chemical analysis and crystal-structurerefinement) by polarized single-crystalinfrared specuoscopy.The crystals span the complete range of chemical variation reportedin vesuvianite,and the spectrashow tremendousvariability. There are 13 recognizable bands(A-M) that can be divided into three types: (1) eight bandsdue to absorptionsat the O/1 site; theseresult from different local cation and anion configurationsat nearest-neighborand next-nearest-neighborsites; (2) four bandsdue to absorptionat O(10); theseresult ftom different local cation and anion configurationsat nearest-neighborand next-nearest-neighborsites, and (3) a low-energyelectronic absorption band. Boron is incorporatedinto the vesuvianitestructure primarily via the substitution B + Mg = 2H + A1. In boron-rich vesuvianite,the four bandsJ-M are not present,indicating that H has been completely replacedby B in the vicinity of the O(10) site. Althougb lacking the fine detail of the principal-stretchingregion, the overtone spectraare equallycharacteristic of this B<+H substitution.The spectrain the principal OH-stretchingregion extendover a very wide spectralrange (3700-3000cm*r;, and show two featurestlat arc of.gencraL lmportance in the qualtitative interpretation of such specffa:(1) the band width increasessignificantly with decreasingband- (from -20 cm-1 at 3670 cm-l to -120 cm-l at 3060 cm{), and (2) the bandintensity is (nonlinearly)correlated with bandfrequency (in addition to H content). Thesetwo featuresare of significancein quantitativelyfitting spectraby numericaltechniques, and in relating bard intensities to compositionalfeatures. Keywords:vesuvianite, infrared spectr4 electron-microprobeanalysis, crystal structure,hydroxyl.

Somntrnr Plusieurssch6mas de substitutionimFliquent ltydrogbne dansla vdsuvianite,et ceux qui ne I'impliquent pas directement afFectentquand m0me le voisinage des anions OH. Par cons6quent,la spectroscopiedes vibrations fondamentaleset des harmoniquesdans l'infrarouge peut fournir une information pr6cieused proposdu degr6d'ordre local. Nous avonse;aminf, ps1 spectroscopiefufrarouge polaris6e sur cristal unique une s6rie d'&hantillons bien caract6ris6schimiquement par analysea h microsonde6lectronique, par voie humide, et par affinement de la structurecristalline. l,es cristaux repr6sententla gamme complbtede variationschimiques d6crites dans la vdsuvianite,et les spectresfont preuved'une variabilit6 imposante.Le spectre comprendtreize bandesdistinctes (A-M) qtrr sont divisibles en trois categories:(1) huit bandesattribu6es aux absorptionsau site OH, qui d6coulentdes diff6rents agencementslocaux des cations et des anions impliquant les prochesvoisins et les deuxibmesplus prochesvoisins; (2) quatrebandes dues i l'absorptiondans le site O(10), qui d&oulent des diff6rentsagence- ments locaux des cationset des anionsimpliquant les prochesvoisins et les deuxibmesplus prochesvoisins, et (3) une bande atfibuable ! une absorptiondlectronique de faible 6nergie.lr bore est incorpor6dans la structuresurtout selonla substitution B + Mg ...- 2H + A1.Dans la vdsuvisniteborifAre, les quatrebandes ,l-M ne sontpas pr6sentes, ce qui indique que le B renplace complbtementle H dansle voisinagedu site O(10). Malgr6 l'absencede rdsolutionfine dansla r6gion de l'6tirementprincipal des ba:rdesOH, les spectresdes harrnoniquessont 6galementcaract6ristiques de cetle substitutionB<+H. Ceue r6gion des spectress'6tend sur un grand intervalle (3700-3000cm-r), et montre deux aspec$drimportance g6n6rale dans I'interpr6tation quantitativede tels spectres:(1) la largeur desbandes augmente de fagon importanted mesureque diminue la fr6quencede la bande,d'environ 20 cfr. I d,3670cm-l jusqu'i environ 120 cm-l d 3060 cm-1; (2) f intensit6des bandes montre une corr6lation non lin6aire avecla fr{uence de la bande,et en plus avecla teneuren H. Cesdeux g6ndralisationsont une importaacecapitale dansI'interpr6tation quantitative des spectreset dansI'attribution desintensitds des bandes aux traits compositionnels. (Traduit par la R6daction) Mots-cl6s:v6suvianite, spectre infrarouge, analyse i la microsonde6lectronique, sffucture cristalline, hydroxyle. 610 TIIE CANADL{N MINERALOGIST

IurrotucnoN TAELE 1. VET'UVTANIIE SAMPLES IJSED FOR INFRARED SPECTROSCOPICWOFK n l@lity Olalitalivo ctmi@l d@dpdon Although the generalarrangement ofthe vesuvianite stucture has beenknown sincethe work of Warren & V4 Tmbac* Lake, N,W,T. F-rlch, low-Al, t gttsFEs+ Modell (1931), there are still details of its crystal V6 L@g trk6 M@, Olden Twp., Ofr. Hch, higFAl chemistry that remain obscure. Groat et aI. (I992a) V6 York Riw, Dungafiqn Twp., Ont. F lch, Iow-Fe showedthat the generalformula of vesuvianitecan be V1 l Jel{roy Mlna, Rlchmond Co., Ouo. Flr@. higFAl, lry-Fe. Tl-fr@ v13 Jsllby Mine, Fichmond Co., Ors. Fn@, hlgh-Al writtenX,nYBTsZnO6sWrc, whereX= Ca Na REE, V23 Laqsl,Ouo. Ffr@. trlgh-F€s,Gs$ Pb2+,sb3+, I= A1,Mg, Fe2*,Fe3*, Mn, Ti, Ct,Ct,Zn, V28 Tompleton Twp.. Ottsw Co., O@. lnt-F, Tidch T = n, B, Z = Si, and 17= OH, F, O2-.A particularly V30 Templeton Twp., Ottawa Co., Ouo. lnt-F. Brlch, low€H important aspectof this work was the recognition (or V31 Wakefidd twp., Ottawa Co., Ore. lrt-F, I-riah rather the re-emphasis)of the importanceof boron in V33 Mmo Clalm, Y.T. tsncn vesuvianitefrom somelocalities. Groat et al. (1992a) Vsg tuiccia, Roms, ltaly Int4, Int-B, hlgttsREE proposedthat B is incorporatedinto ttle vesuvianite v46 Lag@ d€l Ja@, Ctthu6h@, Medoo lm-F, irt-B v49 Bal@histan,Poklstan Fdch Ti-ir@, high-Al, low-Fo structure particularly Hlndlb8gh, via a substitutionthat is difficult \/75 Wlui Riwr, Yalqbkays, Rusda F{r66. Rrlch, lw-oH to recopize solely on the basisof electron-microprobe ALA Val d'Ala. Piomorne, ltely data: B + Mg * 2H + N. This situation is further cEM Teuqnia complicatedby the fact that B also canbe incorporated by a mechan:ismthat involves the substitutionof REE for Ca at the X positionsin the structure. Groat et al. (L994a) showedthat B occurs at two distinct sitesin the structure,sites that are unoccupied adhesive. in B-free vesuvianite.The local details around these sites are somewhatobscured by extensivepositional Chernicalanalysis disorder. Nevertheless,it is apparentthat B locally replacesH in the structure. Many important substi- Chemical analyseswere done with a JEOL 733 tutions in vesuvianite involve variable amounts of electronmicroprobe fitted with one energy-dispersion hydrogen incorporated via (OH)- = 02- exchange. spectrometer and four automated - Becauseof this, infrared spectoscopy in the (OID- dispersionspectrometers. A detaileddescription of the stretching region should be a usefirl probe of local analytical procedures was given by Groat et al. stereochemicalvariations in the vicinity of the O(10) (L992a).For some samples,H2O and Fe2+/Fe3+ratios and OH sites in the vesuvianite structure. were determinedas describedby Groat et al. (L992ay Consequently,this study was initiated in parallel with Becauseof the amount of samplerequired for these the concurrentwork on the chemistryand structureof measurements,bulk sampleshad to be used for all vesuvianite(Groat et al. I992a,b, 1993,l994ub). crystals, including those showing sector zoning; thus we haveno direct information on the variation of these E:rpsRNB{TAL componentsin single crystals.

The samplesused in this work are listed in Table 1; In{rared spectroscopy the letter coding correspondsto that of Groat et al. (1992a).Oriented sectionsof single crystalswere cut Infrared spectrawere measuredon a Nicolet 60SX using, where possible, the external morphology as a FTIR spectrometerfitted with a rotatableglan-Foucault guide, and the orientations of the resulting sections LiIO3 crystal polarizer; aperhres (50-200 pm in were checked by optical interference figures. For diameter) were used to limit the area of the sample sampleswith no exlernal morphology, crystals were exposedto the beam.Crystal fragments were examined oriented by X-ray precessionphotography, sunk into with a polarizing-light microscope,and points were a block of 5-minute@epoxy and then sawninlo slices selectedfor measurementon the basisof crystalquality of appropriate orientation and thickness. Sections (absenceof alteration,cracks and inclusionswithin the 2.04.5 mm thick were groundand doubly polishedfor field of the aperture);the crystal was tlen orientedon optical and electron-microprobemeasurements. The a polarizing microscope prior to insertion into the sections were then removed from the glass slides, spectrometer. remountedwith Crystalbond@adhesive, handground to a thicknessin the range 1G-90pm, dependingon the Rssulrs H content,and then polished.Most sectionswere then removedfrom their glassslide with acetone.Some very Chzmicalana$sis delicate sampleswere left mounted;for these,it was necessaryto subtract a backgrounddue to the glass Compositionaldata for the crystals of Table 1 are slide andalso to removetle spectralcontribution of the given in Table 2. The unit formulae were calculated TIIE INFRARED SPECTROSCOPYOF YESIIWAMTE 6Ll

TABtf 2. AVERAGECHEMICAL COMPOSfiONS (wt%) AND UNff FORMUTAF OFVESLMANI'TECRYSruS USEDFOR INFRARED SPECTROSCOPY v4 V5 v0 vt1 v13 v23 v28 V30 V31 V33 V38 v49 w6

sio2 36,22 36.56 35.92 36.85 36.53 37.56 36.80 34.83 36,76 37.64 34.99 3e.39 37.01 30.00 Alro. re,oo:lie.go t6.91 t8,29 17.go 17.96 16.16 i1.31 1a.47 17.s3 12.go 16,21 1a.8t 1'1.72 T'ior |,/1:} 0.96 1.14 0.00 0.60 0.00 2.77 0.94 2.73 0.67 1.30 O.73 0,00 0.34 MsO 1.57 1,77 2.72 1.8o 1,71 2.66 1,7A 4,74 1.56 1.7A 4.ag 3,93 r,96 A,76 MnO 0.36 o,4O O,7a 0.89 0.06 0.18 0.00 0,25 0.00 O,74 O,27 0,19 0.78 0.08 F6O 2,38 2.86 1.gl 1.14 1,36 0,29 2,61 6,32 2.7O 3,i6 d,O7 g,A4 0.60 1,86 tu2o".. 3,06 1.18 1.83 1,11 ^ O.37 - 2,99 cao 34.78 36.33 34.27 36,17 35.66 36.85 36.97 33.11 36.58 35.43 34.63 36.90 38.29 35.60 NaaO 0,17 0.03 0.03 0.07 0.00 0.00 o.13 0.01 O.23 0.10 0.00 0.00 O.Oz 0,00 Ln,O"** 0.10 0.00 0,97 0.00 0.00 0.00 0,00 3.16 0,00 0.00 1.58 0.00 0.00 0.10 qOs 0.00 0.o0 0.00 0.00 0.00 0.o0 0.00 2.90 0.00 0,00 1.77 1.47 - 2,83 F 1.97 2.26 2.44 0.00 0.O0 0.o0 1,30 0,75 .1.55 3,10 0.73 0,32 2.66 0,2A q 0.19 0.04 0.8'l 0.00 0,01 0.00 0,2'l 0.00 0.16 0.00 0.00 0.00 0.00 0.00 HrO. 1.56 1.7O - 2.77 - 1.83 - 0.61 H:O' 1.53 1.49 1,32 2,A2 2.66 2.78 1.79 0.60 7.A7 1.31 1.89 1.49 1.59 0.87 99.76 99.99 98.22 98.48 98.11 99.29 99.50 97,83 99,40 101.83 98.98 99.13 100.31 98.83 O-F,CI 0.91 1,01 1,21 0.0o 0.00 0,00 0.60 0.32 0.68 __1,31 o.31 -_0.L4 1.12 0.1'l TOTAL 98.84 98.98 97,O1 98.48 98.11 99.29 98.90 57.61 98.72 100.62 A8,67 98.99 99,19 58,72

TABLE 2. condnuod. V6 vl't v13 v23 v28 v30 v31 v33 v3s v46 v49 w6

si 17.98 18.03 18.16 19,02 18.03 18.19 18.13 18.06 18.13 18.28 17.64 17.97 18,02 17,92

AI 9.36 9.83 9.47 10.83 10,4',1 10,26 9,32 6.91 9.67 9.94 7,13 8,68 10.79 6,88 Tr{ 0.53 0.36 0.4:l 0.00 0.22 0.00 1.03 0.37 1.01 0.25 0.62 0.64 0,00 0.13 Mg 1,16 1.30 2,O5 1.31 1.2A 'l.85 1.29 3.66 1.16 1,28 3.63 2.89 1,42 5.01 Mrf' 0.15 0.17 0.33 0,37 0,03 0,07 0,00 0.r 1 0.00 0.31 o.12 0.08 0.32 0.03 Fee+ 0.99 1,18 0.81 0.47 0.56 o,12 1,08 2,31 1,11 1.29 2.'t4 1.50 0,24 0.46 F€3t 1,14 0.44 0.68 0.r+0 0.00 0,14 - 0.66

18.60 18,e7 18.66 18.96 18.81 19,12 18.98 18.39 18.80 18.46 18,71 19.00 r 8,93 18.99 Na 0,10 0,03 0.03 0,o7 0.00 0.00 0,12 0.01 0.22 0.09 0.00 0.00 0.07 0.00 Lnai 0.02 0.00 0.18 0.00 0,00 0.00 0,00 0,80 0.00 0.00 0.30 0.00 0,00 0,01

B 0.00 0.00 0.00 0.00 0.00 0,00 0.00 2,ao 0.00 0.00 1.64 1.26 2,43 F 3.09 3,53 3.90 0.00 0.00 0.00 2.o3 1.23 2.42 4.77 1.16 't.00 4.08 o.M 0.10 0.03 0.6s 0.00 0.ol 0.00 0.18 0.00 0,13 0.o0 0.00 0.00 0,00 0.00 OH a.17 5.89 4,44 9,21 8.39 a,s7 6.89 1.74 5.61 6.29 6.34 4.91 5.16 2.O3

f,x 18.08 't8,70 19.7A 19.01 18.81 19.12 19.11 r9.00 15.O2 18,56 19,00 19,00 19,00 19,00 '13.27 'Y 13.32 13.10 12,97 13,1e 12,69 12.77 13.30 12.86 13.2'l 13,O7 13.87 r 2.98 13.26 z 17,98 '18,03 18.16 18.02 18,03 18,19 18.13 18.06 18.13 18.26 18.00 17.97 18,O2 17,92

rAnalysss of boron-bearlng vosuvianite are normalizsd on 1 I X-catiom; those of boron-ftee vesuvianits on 60 totsl cafions. ('1992a). + - tt rMsasured. tcalculatod, " F€lOsvaluos taksn from Groat atdl. - not dotefmlnod. krrO. - REEcontsrt. Addhlonalcomponsnts (wt.%): V4, Cs:Os0.10, V6, tazos 0,29, Co2Os0.68; V30, LarO31.17,C62Oa 1.55, Pr2O80,10, Ndeos0,19, Gdaor0,09j V33, BeO 0.16; V38, Lasos O.84, CatO"O,74tY49, CuO 0.56: W6, BsO 0,03, k2O3 0.09, Ca2Os0,22,

according to the recommendationsof Groat et el The polarized spectrain the fundamentalhydroxyl- (1992a). stretching region (3000-3800 cm-t) and the flrst overtonehydroxyl-stretching region (6500-7500cm-t) Infrared spectoscopy are shown in Figures I and 2. Band positions are 612 T1IE CANADIAN MINERALOGIST

ABCDE F ABCDE Vesuvianite {tool E//c Vesuvlantte (1001E penp c

o, L' c (, o L (f, a, tt

10

0 o 3800 3600 3400 3200 3000 3800 3600 3400 3e00 300 Wavenumbens(cm-l) wavenumbens(cm-l ) Frc. 1. The polarizedabsorption-spectra of vesuvianitecrystals in the principal hydroxyl-strerchingregion: (a) E ll c; (b) E l- c; bandpositions are shownby the vertical lines, with the bandlabel at the top of the figure.

markedby vertical lines, and band labels are given on intensitieswere measuredfrom the absorbancespectra eachfigure. Band positionsand polarizationsare given with a mm scaleafter interpolationof a backgroundby in Tables3 and4; for the polarizationbehavior, relative eye. We had originally intendedto measurethe inten- TIIE INFRARED SPECTROSCOPY OF VESUVIAN]TE 613

A' Br gDl FF A' B' Ct Dt

Vesuvianl Vesuvtantta (tool V/c (1001E penp lt

o IJ c @ .q L o ID ,cl ,* lllk ll

o.4

o.2 0.2

o.0 o.o 7400 7200 7000 6800 6600 7400 720A 7000 6800 6600 Wavenumbens(cm-1 ) Wavenumbens(cm-l ) Frc. 2. The polarizedabsorption-spectra of vesuvianitecrystals in the hydroxyl-strerchingovertone region: (a) E ll c; (b) E I c; legendas for Figure l.

sities of the absorptionbands for all spectrausing non- each spectrum,and the band overlap is extreme.The linear least-squaresrefinement. This turned out to be band shapeis very non-Gaussian.Much experimen- completely intractable. There are up to 14 bands in tation with band shapeled to the conclusion that a 6L4 TIIE CANADIAN MINERALOGIST

TABLE3, BANDPOSMONS AND PCTLARIZATTONS'IN THE Srnucn nal CoNsonnatoNs PRINCIPALOH.STRETCI.IING REGION OF VESWIANITE Band Position(cm-l) E[c ELc Site Although most (if not all) vesuvianitecrystals show A 3870 84 16 OH evidenceof departurefrom tetragonalsymmety, we will refer to the structure in terms of a tetragonal B 3835 82 18 OH model. Although hieh-2V crystals do show slight c 3696 s OH variations in intensity of the principal OH-stretching D 3567 85 OH bandswith orientationin (001) sectionsnthis is a very E 3624 -80 -24 OH minor effect comparedwith the spectal differences F 3447 76 26 OH accompanyingcompositional differences. The hydroxyl anion can occupy two sites in the G 3430 ss OH vesuvianitestructure, the Oll site andthe O(10) site; in H 3383 s OH order to distinguish betweenthe hydroxyl anion atd 'too I 3240 the OH site (which may be occupiedby hydroxyl or J 3210 100 - o{10) fluorine), we write the former as (OID-. Both ball- K 3156 1@ - o{10) and-stick and polyhedral representationsof the O1l are shown in Figure 3. Each OA site is L 3120 100 - o{10} environment X(3) sites, - coordinatedby cationsat the Y(2), Z(3) and M 3054 100 o(10) and the O-H bond makesan angle of -30' with the c r band intsnsities are normalized to lOO for 6.achspoctrum; axis. Bond-valencearguments (e.9., Yoshiasa & ss E v€ry strong. s a strong, w = weak, yw = vory woak. Matsumoto 1986) show that the OH oxygenacts as a stronghydrogen-bond donor, the acceptoranion being O(7). The cations coordinating OO IZ(2) and X(3)l contributeonly -1.7 v.u. to the anion,and the contri- TABLE4. BANDPOSMONS AND POLARIZATTONSIN THE RRST -0.3 OH-OVEATONEREGION OF VESI,MANITE butionof v.u. from the OH...OQ)hydrogen bond for satisfactionof the bond-valencerequire- Band' Posidon (cm-t) rE[c +Etc fundamental irrol2lF is needed ment at the O(7) anion. 7176 The O(10) environmentis illustrated in Figure 4. a',70947380.97A The O(10) site lies on the 4-fold axis down the channel q7016a2C0.975 throughthe sftucture.It is coordinatedby one Y(1) and D'696882D0.977 fourX(3) cationsin a squarepyramidal arrangement. In E',07808260.962 boron-freevesuvianite, the O(10) site is fully occupied; in boron-bearingvesuvianite, O(10) is only partially 4746 a 2 F 0.967 occupied.There have beenvarious proposalsas to the K 6930 w - K 0.939 identity ofthe anionoccupying the O(10) site.The only point ' th€ ptimedlstters arc usodto distinguishovortone bands from direct evidenceon this is the neutron structure- fundamentalbands; refinementoflager et al. (1989),who locateda hydro- rr ro and lF are the frequenciasof tho ovsrtoneand fundamental gen (/4 position asymmetricallyplaced betweentwo bands,rssportivslyt -23 r band intensitiosar€ normalizedto 10 for eachspactrum, except O(10) atomsseparated by A along the 4-fold for K', in whichthe bandis not visiblein th6 EJ.c aDactrum. axis parallel to [001]. This Il site is partly occupied (occupancy= 0.85); the H was assumedto be locally disordered,directly bondedeither to the upper O(10) oxygenor to the lower O(10) oxygen.The detailsofthe geometry around the O(10) site in boron-bearing Pearson-Yll function (Howard & heston 1989) best vesuvianitewere reported on by Groatet al. (1994a).In fitted the data,but the broad tails that occur with this addition, Gtoat et al. (1992a) have shown that the shape produced major uncertainties in the fitting amount of H is very variable, although the local process;slight changesin the shapefunction produced stereochemicaldetails of this variation are as yet major chtnges in the final fit. After much effort, this unknown. approachwas abandoned. In somecases, it was not possibleto measureboth Polnizstion behs.vior overtone and fundamental specfta owing to sample constraint$,primarily the presenceofnumerous cracks, There aretwo distinct H positionsin the vesuvianite inclusions, and alteration in some of the samples, structure,I(1) associatedwith the OH site, nd H(2) There is no evidencefor H2O groups in crystalline associatedwith the O(10) site. For a completely vesuvianite,although spectral features characteristic of orderedstucture, one would expecttwo bandsin the H2O were observed in radiation-damagedsamples fundamental region, each correspondingto one of ff-by et al.1993). the G-H bonds.In a disorderedstructure. these bands TIIE INFRARED SPECTROSCOPYOF VEST'VIANITE 615

Flc. 3. The OI1 environment in boron-free vesuvianite in both ball-and-stick and polyhedralrepresentations. D can split owing to variations in local environment. According to the long-range stuctural information available,the polarizationbehavior ofthe bandsfrom I eachof the two H environmentsshould be significantly different. H(2)hes on a 4-fold axis, and the O-H bond is alongthis axis, exactlyparallel to the c axis; in addi- non, H(2) hydrogen-bondsto the neighboring O(10) anion, also on the same4-fold axis. Thus the funda- mental absorptionin the ffiared will be completely polarized, with maximum intensity E ll c (electric vectorparallel to the c axis); it will have zero intensity where E l- c. Conversely, the I(1) position is so arrangedthat the OH-H(I) bond makes an angle of -30o with the c axis. Thus the infrared fundamental band resulting from this bond will be partly polarized, with E lJc strongerthan E l- c. Consequently,we can differentiatebands due to O(10)-HQ) andOH-H(I)by their different polarization-behavior. Preliminary assignmentof the bandsin the fundamentalhydroxyl- stetching region accordingto this criterion is shownin Table3.

Local configurationsaround OH

It is well known that local disorder at cation posi- tions coordinatedby the donor anion of a hydrogen- z bondedconfiguration can produceseveral bands in the fundamental hydroxyl-strerchingregion, each corre- I spondingto a different local configuration @ossman Y 1988,Hawthome 1981). A sketchof the relevantlocal XI- geometryfor the OIl anion is shown in Figure 5. In FIc. 4. The O(10) environment in boron-free vesuvianire the linear trimer of edge-sharingoctahedr4 I(2) is the viewedalong [100]. cental octahedron"the two flankins octahedra are 616 TTIE CANADIAN MINERALOGIST

(a) (b) (c)

(oH)e OHF Fz

Frc. 5. Idealized sketch of the OIl position and neighboring polyhedra: (a) the linear Y(2)=Y(3)=Y(2) edge-sharingtrimer with hydroxyl at both o// positions; O) y(2)=f(3)=f(2) trimer with one hydroxyl and one fluorine; (c) Y(2)=Y(3)=YQ) trimer witl two fluorine atomsat the Oll positions.

Y(3), and the correspondingsites can potentially be in two different ways: F may replace(OII)- at one of occupiedby Al, Fe (Fe3+and Fe2+),Mg and Ti. There the two OII sitesin the trimer to producethe (OH|-F aretwo OIl sitesin this trimer, alranged1n a trar?^tcon- local arrangementshown in Figure 5b; alternatively' figuration relative to the I(2) octahedronand occurring F may replace (OH)- at both OH sites to produce as part of the edge sharedbetween the Y(2) and I(3) the F-F local anangement shown in Figure 5c. octahedra.It is clear that variation in occupancyof the Replacementof one (OHf by one F (Fig' 5b) will Y(2) and I(3) sites have the potential to produce eliminateone hydroxyl band,and canpotentially cause distinct bandsin the infrared region. Each O11site is an inductive shift in the bandfrom the remaining(OH)- coordinatedto one I(2) and one I(3) cation; it is also tra/Lsta the substitutedF anion. Replacementof both adjacent to an X(3) cation; however, the X(3) site (OH)- anions by F (Fig. 5c) will eliminate fwo shows insufficient variatron in occupancyto produce hydroxyl bandsand will give rise to no new hydroxyl significant multiple bands.Consequently, the number bandsfrom this specific trimer. Hencethese two local ofbands will be equal to the numberoflocal configu- schemesof order producevery different results in the rations possibleat Y(2) and f(3) within the constraints infrared specfra. of the known bulk-chemistry and cation-ordering Comparisonof spectrafrom crystalsof fluorine-free patlerns.Not all of thesebands may be resolved(owing and fluorine-bearingvesuvianite will give an idea of to accidentalband overlap or insufficient intensity of the local alrangementsinvolved. Inspectionof Table 2 the bandsabove background). showsthat Vll andV49 havevery similarpopulations Incal arrangernentsof cations:The resultsof crystal- of cationsbut very different F contents[<0.3 atomsper stucture refinement(Coda et al. 1970,Rucklidge er al. 1975,Giuseppem & Maza 1983,Valley et al. L985, Yoshiasa& Matsumoto 1986,Fitzgerald et al. 1986a, b, 1987,Gto t et al. 1992b,1994b) show that tJreYQ) site is virtually entirely occupiedby A1. Hence, with about the OH site, the regard to local configurations TABLE 5. POSSIBLE LOCAL CONRGUNATIONS ABOUT Y(2) site is fixed (=Al), and any variation occurs at THE Of'POSI]'ION IN THE VESWIANITE STRUCTURE the Y(3) site. According to the general chemistry of Configuration I yt3)-y(2)-oH/Fio vesuvianite (Groat et al. 1992a), the I(3) site can Boron-lrge Boroftboaring potentially be occupied by the following l-group cations:Mg, Fd+, Al, Fe3+,Tie. However,crystal- 1 Ms-Al-OH Ms-Al-oH stucture refinementsof low-Fe Tibearing vesuvianite Fe2+-Al-OH Fs2+-Al-OH (work progress) be orderedat the crystals in showTi to a At-At-oH Al-Al-oH Y(1) site. Thus Ti+ is not a significant occupantof Fe3*-Al-Oh the I(3) site, which thus can be occupiedby Mg, Fe2+, 4 Fe3*-Al-oH Al andFe3+; hence there arefour possiblelocal cation- 5 Mg-Al-F Mg-AFO-B configurations about the OH site in vesuvianite 6 Fa2+-Al-F Fe2+-Al-o-B (Iable 5). 7 AI-AI-F At-At-o-B Incal arrangementsof anions: Each Y(2) [=Al] cation 8 Fe3+-Al-F F€3*-Al-O-B is adjacentto t.lro OH sites in a trans configuration (Fig. 5a).Fluorine may be incorporatedatrhe OH site . 1,131- 1Mg.Fe"*,Al.Fo3');X2) = Al TIIE INFRARED SPECTROSCOPYOF VESIryI.ANTTE 6t7

Local configurationsarounl O(fi)

A sketch of the relevant local geometry for the O(10)anion is shownin Figure4. The O(10)anion is coordinatedby four X(3) cationsand one I(1) cation. In most crystals,X(3) is completelydominated by Ca, and the only variable occupancyof cations around O(10)involves the I(1) site,which may be occupiedby Feh, Mg, Ti and possibly-minor Al and Fe3*1iy lplus C*+, Zn andpossibly Mn3+ in exotic varieties).Most 36@ 34@ 32N structure refinements have shown transition metals Wavenumbas(cn') (generallyFe2+ and Ti) to dominateat the I(1) site,but other cations (e.g., Mg, Al) have been detected,and hencemultiple bandsmay result. The O(10) anion may also be occupiedby F (Groat et al. L99'2b),which altersthe strengthof the hydrogen o 1-5 bondfrom the neighboringO(10) hydroxyl anion, also o 11 potentially producing new band(s) in the hydroxyl- F stretchingregion; as shovrnin Figure 6, Vl l € r.o and V49 3 show significantly different behaviorin the low-energy ' region (300G-3300cm-l), suggestingthat this is the 0.5 case.

0.0 GSNERAL FEATURTs oF THE SPECTRA 3800 3600 3,f00 3200 30m Wavenumbers(cm-') Inspectionof Figure 3 showsthe exffemevariability of the polarizedffiared spectra Ftc. 6. Comparisonof the polarizedabsorption-spectra of vesuvianite.Bands of Vl I A-H and V49 in the principal hydroxyl-strerching region. and J-M have been assignedto local OH and Vll and Y49 have the sameproportions of cations, and O(10) configurations, respectively, but the detailed differ only in their fluorine content; Vll is verv low in assignmentof individual bands remains to be done. fluorine (< 0.6 F apfu), whereas V49 is fluorine-rich Thereare two additionalfeatures of the spectrathat are (4.1F aptu). rather enigmatic. Firstly, the ,, which is promi- nent in the E I c specfraof Vl1, V13A and GEM, is incompatiblewith the orientationof the (OH)- groups at the OH and O(10) positions.Secondly, many of the spectra also seem superimposedon a very low- formula unit (apfa) versus4.Lapful. Figure 6 compares amplitude absorption that extends down to the polarizedabsorption-spectra of thesesamples in the principal hydroxyl-stretchingregion. The spectraare strikingly different in both polarizations, indicating that the substitution (OI!-is of Ffor both suppressing 1.0 somebands and giving rise to new bands;in particular, v:m bandA is lost, and bandB is weakened"whereas other bands,such as F and D, are new or occur with ereatlv () 000)V/o increasedintensity. Hence the (Olt)--F urr*f"*"ot <) str (Fig. 5b) is of major importancein decipheringthe €o o.s local patternof orderaround the OfI site in vesuvianite. q There are an additional four possiblelocal configura- tions due to F at the next-nearest-neighborposition (Iable 5), giving a total of eight bands from the Oll position. The F-F' configuration produces no 0.0 new bandsoand thus is not directly "visible', in the 4m0 3500 3000 75w hydroxyl-stretchingspectra. However, the very large Wavenumbers(cm") effect produced by the incorporation of -4 F apfu (Ftg. 6) into the structure,greatly reducing some bands Frc. 7. The E ll c absorption-specfraof V30 in the principal hydroxyl-sfetching frequencyregion, and producing new dominant bands, indicates that with an expanded range either side of the -ajor absorptions. (OH)--F configurations must dominate Note the over F--F broad low-amplitude absorption that extends down to configurations. -2800 cm-r. 618 TIIE CANADIAN MINERALOGIST

-2500 cm-1; this is shown in an expandedrange for 3500and 3000cm-l, andthe very broadbands. There (Table the E ll c spectrumof V30 in Figure 7. This absorption are (at least) nine discernablebands 3), and is a real featureand is presentin many of the spectra. thereis also the suggestionof fine structurein someof The previous discussiongives a generalframework the bands.The spectrafor Vll and V23 are similar, within which we can now attempt a detailed assign- showingonly minel differencesin resolutionand band ment of all bandsin all spectra,taking into accountthe intensities that can be related to minor differencesin variation in chemical composition of the crystals composition.These compositions show a prominent 1 examined.Initially, we will consider the spectra of band whose polarization is incompatiblewith current boron-freevesuvianite. ideas on the configurations of hydrogen-bondingin vesuvianite.This bandis also of very unusualshape. It Bonox-FpssVnsuuaNrrs is centered at -3240 cm-l, but its low-energy tail extends down to -2800 cm-r (Frg. 7). Figure 8a Although the spectra in this group show broad suggeststhat this band is fairty symmetrical;if this is similarities, there are significant variations that the case, a considerableamount of the absorption correlatewith changesin composition,specifically the intensity in the higher-energyrange (above 3400 cm-l) extentof the F= (OtI)- substitutionand the natureof will be due to the high-energytail of this band. This the cation substitutions at those sites that directly will significantly affect our estimateof the intensities coordinatethe Otl and O(10) sites. of the bandsin this region, and requiresfurther con- sideration;this will be donelater. F luorin e-fr ee ve s w ianite The corresponding overtone spectra for V13 (Frg. Sb)are significantly lesscomplex than the spectra The spectraof V13 areshown in Figure 8. The (100) in the fundamentalregion, but still show considerable spectrum(Frg. 8a) showsvery strongpolarization, with detail. Again, the polarizationdependence is E ll c > B maximum absorbancewhere E c. The spectrumis -L c for atl bands.The principal featuresare a partly ll -7170 very unusual,rvith its continuousabsorption between resolveddoublet at -7130 alid cm-r, with much weaker and broader bands at -6800 and -6960 cm-1.The specta of Vll are similar, excePt that there is a singlJbroad band at -6850 cm-l rather 2.5 thanthe two absorptionsseen in V13.

2.0 (a) ll Yffi Fluorine-b earing vesuvianite {) c) F 1.s Spectrafor V4 (3.5 F aptu) are shown in Figure 9. 'k There are six principal absorptionsand a broad sloping E r.o shoulderat -3400 cm-l in the E ll c spectrumof the ? principal hydroxyl-sftetchingregion. As with fluorine- 05 free vesuvianite,the absorptionin both polarizations has a significant low-energytail that extendsdown to 0.0E -2500 cm-I. The enigmatic/ band is presentalso in 3600 3400 3N 3800 3m the E J- c polarization, but is much weaker than in Wavemrmbers(cn') fluorine-freevesuvianite (e.9., Fig. 8a). The correspondingovertone spectra for V4 are V5 and V49 are very 0.3 shown in Figure 9b; spectrafor similar exceptfor slight differencesin resolution.The (b) / \ v13Gm):,** principal feature is a partly resolved doublet at OEoverboes -6960 and -7010 cm-l, with a much weakersingle I o.z band at -6740 cml; polarization dependenceis 6 Ellc>EIc. o a Samples V6, V28 and V3l contain interrnediate € o.r amountsof F (-2.0 apfu); by and large, the spectra (Frg. 10) are intermediate between the spectra of fluorine-freevesuvianite Grg. 8) and thoseof fluorine- 0.0 rich vesuvianite(Fig. 9). The specfraofV28 (Fig. 10) 74ffi 72W 7m 68m 6600 show considerabledifferences from the spectraof V4 Wavenumbers(cm') (Frg. 9); positionsand polarization dependencies ofthe major bandsare the same,but the band intensitiesare Ftc. 8.The polarized absorption-spectra offluorine-free vesu- radically different. In addition, the E l- c spectrum vianite Vl3 (a) in the principal hydroxyl-sffetching showsless fine-structure in V28. region, and @) in the hydroxyl-stretching overtone region. TIIE INFRARED SPECIR.OSCOPYOF YESIIVIANTTE 619

3.0 (a) 1 veorviorib (a) f\ A vewffi v40m) rzJ (100)

H z.o gI z.o 6 G' € 'k a a € r.o t r.o

0.0 t- 3600 3400 3200 3m 38m 36(p 3@ 32j0 Wavenumbers(cn') Wan'enumbers(cn')

1.0 0.3 (b) vesuviroib (b) ytrxP v4 (100) A \r28Gm) |l) 0Eoverbnes OEovsbles a 8 o.z €N o.s o 4 q € o.r o

IC 7400 72!0 68@ Wavenumbers(cm') Wavenumben (cn') Flc. 9. Thepolarized absorption-spectra offluorine-rich vesu- Flc. 10.The polmized absorption-spectra of fluorine-bearing vianiteV4 (a)in theprincipal hydroxyl-strerching region, vesuvianiteV28 (a) in the principalhydroxyl-strerching and@) in thehydroxyl-strerching overtone region. region,and (b) in thehydroxyl-stretching overtone region.

The overtonespectra for V28 differ somewhatfrom -6960 cm-l, and there is a broad doublet to higher those of V4. Insteadof an obvious doublel there is a energies with component bands at -7160 and strong single band at -6970 cm-l, with a slight -7100 cm-l, respectively.In addition, thereis a broad suggestionof a shoulder at -7010 cm-l. There is a weak band ar -6770 cm-I. The spectraof V38 are low-energy band at -6750 cm-1 that is very syrnme- similar, exceptthat the doublet characterof the high- trical. The other significant difference from V4 is the energyabsorption is not apparent. prominentshoulder at -7 1?-0cm-t in V28; comparison Comparisonof the spectraof sampleswith different witl V4 doesshow a slight asymmery in the tail of the boron contents@ig. 12) showsthe dramatic spectral sfrongdoublet, which could correspondto a very weak differencesproduced by the incorporationofboron into analogueof the prominentshoulder in V28. the structure.Both the OH (bandsA-A and the O(10) (bands.f-M) regions are affected, indicating that the BonoN-BBnnnvcVpsuuexrrr direct substitutionof boron for hydrogen,B + Mg = 2H + Al, proposedby Groat et al. (1992a)affects both The specta of V75 (2.4 apfu B) are shown in hydrogen positions. Detailed structural work (Groat Figure 11. There is an extemely strong absorptionat et al. L994a)shows that boronreplaces hydrogen at the -3580 cm-l, with subsidiarymaxima at -3630 and OIl position (Frg. l3). This obviously destroyscon- -3480 cm-l, and thesehave very strong polarization, figurations 1-4 (Table 5) and gives rise to new with maximumabsorption for E ll c. At lower energies, configurationsspecifically resulting in bandsD andF:, there is a broad absorptionat -3150 cm-l that is these are also present in crystals of the boron-free presentin the E ll c specnumand is completelyabsent fluorine-rich vesuvianite,indicating that althoughthese in the E 1c spectrum.In addition, thereis the sugges- bandsare at approximatelythe sameenergy, they arise tion of somefine-structure in the high-energyband at from different local atomic configurations in the -3680 cm-l. srucnne. The overtone spectra (Fig. 11b) show intensities There is anotherkey differencebetween the spectra E ll c > E I c. The strongest band occurs at ofboron-bearingand boron-free vesuvianite. For E I c 620 THE CANADIAN MINERALOGIST

5 (d (a) A Y3xgd" {ffi 4 () q)

G 3 H q 2

1

0.0 0 3800 3800 3600 34@ 32W Waveirumbers(cm-')

([) Veswiaitb 0.3 (1m) Bperp c (o Veswianib C) w5 (100) q I o.z OE ov€ablfd € a

A q Ic t 0.1 1c (b) 3ffi 3400 32W Wavenumbers (cm-') 74{o 72co 7@0 6800 66m Wavenumbers(cn') FIG. 11. The polarized absorption-spectraof boron-bearing Frc. 12. Comparisonof the spectraof vesuvianite crystals vesuvianiteV75 (a) in the principal hydroxyl-stretching V13A, V38 and V75 in the principal hydroxyl-strerching region, and (b) in the hydroxyl-stretchingovertone region. region, showing the effect of different amountsof boron on the appearanceof tle spectra: (a) E ll c spectra; @)Efcspectrum.

@ig. 12b),the spectraof boron-freefluorine-free vesu- strongly suggests that this band is due to the presence vianite show a prominent . that is absentin the ofhydrogen. spectraof boron-bearingvesuvianite; this observation

OH o(4 W W Q n(t i i ': H(1)t W W o(7) OH o(7) OH Frc. 13 . The B + Mg -->2H + Al substitutionin the vicinity of the OIl sites (from Groat et aI.1994a\. TTIE INFRARED SPECTROSCOPYOF \IESI'VIANTTE 62r

BANDINTENSI]Es N THE ltke 2:l or 3:2 than8:1 (omittingthe 1 bandfrom con- PRNcFALOH-SrnBrcHnrc RsctoN sideration).This suggeststhat the molar absorptivity increasessignificantly with decreasingband-frequency There have been many attemptsto correlate band [albeit less so than that suggestedby linear extrapola- intensities in the principal OH-stretchingregion with tion of the curve for amphibolespublished by Skogby cation occupanciesat the sites coordinatingthe (OH)- & Rossman(1991)1. anion [seeHawthome (1981) and Rossman (1988) for reviews]. By and large, ttreseattempts have not been Bel*o Wnrs As A FuNcrroNoF FREeUENcY very successful.There are severalreasons for this, one of the more important being the fact that the molar At the high-frequency end of the principal OH- absorptivity of an absorptionband in this region is s6elshingregion, the A band is quite sharp(half-width strongly relatedto the frequency(energy) ofthe band. = 20 cm-l), whereas at the low-frequency end, the Skogby& Rossman(1991) have shown that the molar bandsare very broad (half-width = 100 cm-t). The absorptivityof OH bandsin amphibolescan vary by a half-width (tull width at half heigh$ of eachband was factor of 3 over a frequencyrange of -100 cm-1.If this measuredwith a mm scalefor those spectrain which type of behavior is generallythe case,it accountsfor the band could be adequatelyresolved by eye. severalof the unusualfeatures observed in the spectra Although a relatively crude procedure,a systematic of vesuvianite. behavior of half width as a function of frequency The rangeof significant absorptionin vesuvianiteis Grg. 14) is apparent;a very well-developednonlinear from -370G-3000cm-l (perhapsin somecases down correlationis presen! the two lines in Figure 14 being to 2500 cm-r), a rangeof 70C-1200cm-r. The vesu- drawn to emphasizethis effect. vianite spectra suggest that the molar absorptivity There are two significant features conveyed by varies significantly over the observedspectral range. Figure 14: (l) the increasedband-broadening with SamplesVll and Vl3 eachhave 8(OQ- at the OH decreasingfrequency, and (2) the nonlinear aspectof positionand l(Olll- at the O(10)position; if the molar this behavior. Feature (1) is due to increasinginter- absorptivity of (OH)- were independentof frequency, actionwith other structuralvibrations as the strengthof tlen the relative intensities of. the OH bands (A-Il) the hydrogenbond increases.Feature (2) doesnot seem shouldbe eight times the intensity of the O(10) bands to have beennoted before, but doescorrelate with the (.I-M). Examinationof Figures6 and 8 showsthat the two different environmentsof H in the vesuvianite relative intensitiesof the two groupsof bandsare more structure.Bands A-Il are associatedwith the OH-H(|)

140

^ 120 L ! roo iBo o =60 -l 540 :E 20

3700 3600 3500 3400 3300 3200 3100 BANDPOSITION (cm-1)

Fic. 14. Band half-width as a function of band frequencyil the principal OH-stretching region for vesuvianitepolarized E ll c; the line is drawn merely as a gurdeto the eye. 622 TI{E CANADIAN MINERALOCIST bond, and constitutethe first (steeper)part of the curve to configurations1-4 in Table5. In V1l andV13, the in Figure 14. Bands J-M are associatedwith the strongestE ll c bandis B at -3630 cm-r; this mustbe O(10)-HQ) bond, and form the second (shallower) dueto configuration3 (Table5). By analogywith other part of the curve. T\e OH-H(\) bond forms a bent hydroxyl-bearing minerals (amphiboles,micas, talc; hydrogen-bondsystem [OH-A(D...O(I) = 160o;Lager Hawthome1981, Rossman 1988), bands due to con- et al. 19891,whereas the O(10)-H(2) bond is part of a figurations involving lighter lower-valent specieswill straiChthydrogen-bond system [O(10)-H(2)...O(1"0) = occur at higher ;thus theA bandwill be due 180'1. It is tempting to ascribethe d:ifferenttrends in to configuration I (Table 5). Figure 14 to this feature,particularly as carefirl studies The most intense bands itr Y49 ue B, D and F ofhydrogen-bondgeometry (Brown 1976)suggest that (Frg. 3), the only I(3) cationsare Al andMg (Iable 6), bent hydrogen-bondsand straight hydrogen-bondsare and there is 4.1 F apfu. Thus the possibleconfigura- energeticallydistinct. If this is actually the case,the tions in Y49 are l, 3, 5 and 7 (Iable 5). We have behaviorshown in Figure 14 shouldbe characteristicof alreadyassigned band A to configuration1, andband A OH-bearingcrystals in general;this is currently under is absentin the V49 spectrum(Frg. 3). HenceF must examination. preferentiallyorder at Ofl sitescoordinated to Mg and Al, producingconfiguration 5 ratherthan configuration DsrAtrtD AssIcN'rrasNToF BANDS: 1. Band B is already assignedto configuration 3, and Tur OH Snn thus bandsD and F must correspondto configurations 5 and 7; note that this in reasonableaccord with the The relative intensitiesof the A-I1 bandswill now occupancyof the Y(3) site in V49. Which of the bands be relatedto the occupanciesofthe I(3) site (aswell as D and F is due to which of the fwo possibleconfigura- the F content),bearing in mind the effect of frequency tions, 5 and 7, cannotbe determinedon the composi- on bandintensity discussedabove; site populationsfor tions ofthe I(3) site only, as the relative in0ensitiesof the I(3) site are shownin Table 6 for the crystalsused the bandsalso dependon the local order exhibited by in this work. F (cl Figs. 5b, c). However, a higher-chargesub- stituentcation usually displacesthe principal hydroxyl- Bo r on-fre e ve s av ianit e stretchingband to lower frequenciesthan lower-charge substituents;on the strength of this argument, we Inspection of Table 6 indicates that the dominant provisionally assip bandsD andF to configurations5 local Y(3)-YQ) configurationmust be configuration 1 and 7, respectively. of Table 5. In particular,samples V11, V13 and V23 We have ascribedthe A, B, D, andF bandsto con- arepoorin fluorine andwill notbe affectedby fluorine- figurations involving Mg or Al at Y(3); the C, E, G, H blocking or additional fluorine-shifted bands; hence bandsmust tlerefore be due to configurationsinvolv- their specframust consistpredominantly of bandsdue ing Fe2+or Fe3+at I(3). The relative weaknessofthese bandsin the spectra(Figs. 3a b) is in accordwith the generallow level of Fe2+and Fe3+at the Y(3) sites in thesecrystals Clable 6).

TABLE 6. APPROXIMATEX3).SITE, F AND B CONTENTS Bo ron-b earing vesav ianite (APFU) IN THE VESWIANITE CRYSTAI.SSTUDIED Mg Fe2+ Fo3+ The incorporationof boron at the Z(1) site (Fig. 13) '1.2 V4 6,2 o,5 t.l 3.1 will have a direct effect on the hydroxyl-stretching spectraas B replacestwo hydrogenatoms and reduces V5 6.7 1.3 o.6 o.4 J.O the overall intensity of absorption(Frg. 12). However, V6 ?o its incorporationcan also potentially have an inductive v1 1 6.7 1,3 effect. Removalof one hydrogenatom in a trimer and v13 6.3 t.z - 0.5 replacementof the H-O bond by a B-O bond may v23 6.3 1.7 inductively changethe strengthof the G-H bond in the (Fig. v2a 5.4 t.5 1.1 2,O tans OH of the trimer 13b), producing a new band in the hydroxyl-stretchingregion. As is apparent v30 2.8 3.8 1.4 1,2 2,6 in Figure 12, incorporationofboron into the structure v31 o.o t.l 1.1 2.4 doescorrelate with a radical reductionin the intensity v33 t.J 0.1 4,4 of the A, B andE bands,and the appearanceor strong v38 2,9 3.5 t.o t.z relative increasein intensity of the D and F bands. 'l.o v45 4.1 2.9 t.4 Above, we have ascribed these two bands to con- figurations 5 and 7, the Mg-Al-F and Al-Al-F v49 6.8 1.2 4.1 configurations.The dominaaceof thesetwo bandsin v75 2.9 4.6 o,4 2,4 the boron-bearingvesuvianite spectra indicates that the TIIE INFRARED SPECTROSCOPYOF VESIryIANITE 623 inductive effect of boron substifutionat the I(l) site TABLE 8. APPROXIMATE XI}.SITE CONTENT' (APFU} (Fig. 13b) is similar to the inductive effect of fluorine IN THE VESWIANITE CFYSTALS STUDIED substitution at the OH site @ig. 5c). This being the Foz+ Fe8* Mg case,we expectband D to be more dominantthan band V4 0.5 0.6 Fin the spectraofboron-bearing vesuvianite, as these v5 0.4 0.6 have Mg greater than Al. However, note that the V6 0.4 o.6 situation is slightly complicatedby the fact that the v11 0.5 0.5 crystals of boron-bearing vesuvianite also contain v13 o.2 0.6 o.2 somefluorine, and hencewill also have somecompo- v23 - o.2 o.4 o.2 nent of the D andF bandsdue to the inductive effect of v2a 1.O fluorine as well as that of boron. v30 o.8 Careful inspection of the F band in the spectraof v31 1.0 boron-bearingvesuvianite 3a, 12) showsit to v33 o.2 0.8 @igs. v38 o.5 o.6 occur at slighfly different frequenciesin the spectraof o.5 (-3485 v46 0.6 the boron-bearing cm-r) and fluorine-bearing v49 o.5 o.2 boron-freevesuvianite (-3470 cm-]), showingthat the w5 0.1 o.7 dominant configuration giving rise to this band is different in eachcompositional variant.

DSTATLEDAsstclwnm oF BANDS: Tm O(10)Snn hydrogen-bondingconfiguration must be dominatedby O-O occupancyof adjacentO(10) sites (Fig. 15a). Bo r on-fr ee ve s uv i anite Thus the K and M bandsmust representoccupancy of I(1) lbonded to (OH)-] by two different cations. Inspectionof Table 7 and Figure 3 showsthat the Inspectionof Table8 showsthat in V13, I(l) is domi- boron-freecrystals fall into two goups; Vl1 andV13, natedby Fe2*owhereas in Vll, I(1) containssimilar andthe rest (V4, V5, V6, V28, V31, V49). Both Vll amountsof Fe2+and (Mg,Al). ThusbandKseems asso- Gtg. 6) andVl3 (Frg.8) showstrong K andM bands. ciatedwith Fe2+occupancy of I(1), whereasband M is Both Vll and V13 are hydroxyl-rich and (nearly) associatedwith (Mg, Al, Fe3+?)occupancy of f(1). fluorine-free; the I(1) site populations (fable 8) are The other crystals(V4, V5, etc.) all contain signifi- approximately[0.4Fe2+ + 0.5(Mg + Al)] and [0.2Ti + cant amountsof fluorine. Groat et al. (1992b) have 0.6Fe2++ 0.2(Mg + Al)1, respectively.The local shown that fluorine preferentially occupiesthe O(10) site, up to 1 apfu; in this case,the dominanthydrogen- bonding configuration correspondsto (OI!--F- occu- pancyof adjacentO(10) sites@g. 15b).The ,/ and.L bands also must representoccupancy of I(l) by two TABLE 7. IA{TB{SITIEST FOR BANDS different cations. Inspection of Table 8 shows these J-M IN THE VEgWANITE CRYSTALS STUDIED cationsto be Fe2+and Tia. As V5 hasFe2+ gteater than Ti4 and J greaterthan l, this suggeststhat band "I is v4 10 associatedwith Fe2+atY(l), andband.L is associated with Ti4f at Y(l). V5 20 4 V6 20 10 vl1 2 30 25 vl3 35 5 (a) (b) (c) (d) v2a 20 15 v30 v3'l '16 10 o(10) F o00) v38 E I I v45 6 H u H I v49 10 n w5 2 2 Alj o(10) o(10) F GEM Fto. 15. PossibleOH-F arrangementsat adjacentO(10) sites: r valueg estimated by eye ftom Fgure 3. (a) OH--OHI G) OH--F; (c) F-F; after Groat et al. rr - denotsaband not obsgrved- (1992b). 624 TIIE CANADIAN MINERALOGIST

Bo ron- bearing ve suv ianite

As noted above,boron directly replaceshydrogen at the H(2) site, leading to significant reduction or even completeloss of intensity in the low-frequencyregion (bands/-M) of the spectrum.It is alsonotable that only onebroad band is presentin this regionin crystalsV38, V45 and V75. In V45 and V75, this band is symme- o trical, but in V38 Gig. l2), this band showsa slight a asymmetry,suggesting that it consistsof two compo- nents; presumablythis is also the case for V45 and 'l-i V75. Thusthe "I andZ bandsare the predominantbands of this region in the spectraof boron-bearingvesu- o vianite, and it is notable that all these crystals do € contain significant amountsof fluorine (Table 2).

OvERTol.rESprcrna

Band positionsare glven in Table 4. Also shownin Table 4 are the correspondingfundamental bands and the ratio f lzDF,where D" and oF are the frequencies of the overtoneand fundamentalbands, respectively; the latter values are a measure of the degree of anharmonicityinvolved in the O-H interaction. The 6s00 6000 5500 Wavenumbers(cm-l)

Ftc. 17.The E ll c overtonespectra of vesuvianitecrystals with (V13, GEM) and without (V5, V30) significant oveftone V€svieiE bandsat 5930cm-I. GE\{ o{) Fo.

q {s. polarization behavior also correspondswith that 'aN \*---*,- ) observed in the fundamental region. Although the -*__*_-_,_- overtonespectra lack the fine detail of the fundamental spectra,they are equally diagnosticofthe behavior of 7C[n 6(m 5m0 the G-H bondsin vesuvianite,and do not require the thinned Wave,numbers(cm-t) sample to be to the same extent in order to recordthe spectra. Comparisonof Figure 3 and Table 3 with Figure 4 0.5 and Table 4 shows that. whereasbands A-F in the fundamentalregion havereadily apparentcounterparts (b) veswiaite o.4 A'-F' in the (fint) overtoneregion, the corresponding ()(l) overtone of the lower-frequencyfundamental bands E 0.3 (especially J and K) are apparentonly after careful '! inspection.In the fundamentalregion, V30 has no,I or ? o.z K bands, whereas GEM has a very strong K band (Fig. 3). Comparisonofthe overtonespectra (Frg. 16) 0.1 showsthat GEM hasa weakband at -5930 cm-l in the E ll c polarization, whereasV30 has no such band. If 0.0 this band is the K' overtone,it should also be present 8000 TCKn @m 5m0 in other crystals with stong K bands. As shown in 'Wavenumbers (cm-') Figure 17,this is the case.Crystal V13 hasa strongK band in the fundamentalregion 3) and also has a Flc. 16.The polarizedabsorption spectra of vesuvianitein the @g. discemableK band at -5930 cm-l; crystals V5 and hydroxyl-strerching overtone region: (a) GEM, which V30 showno Kband andweak.I and I bands.and have shows a weak band polarizedE ll c at -5930 cm-r; (b) V30, which showsno bandnear 5900 cm-r. no relatively strong band in the 5500-6500 cm-r THE INFRARED SPECTROSCOPYOF VESWIANTTE 625

Low-Tmaprnarunr Sprc"rna

In an effort to increasethe resolutionof the spectr4 a few sampleswere run at the temperatureof liquid N2. Figure 19 showsthe polarizedlow-temperature specta for Vll in the principal OH-stretching region. Comparisonwith the room-temperaturespectra (Frg. 6) 6 o.so shows that although the bands sharpensomewhat at low temperature,no additionalbands are observedas a result of this slightly increasedresolution; however, note that the very broad absorptionat -3230 cm-l in the E l- c polarizationstill extendsdown to well below 3000cm-I.

Sumraanv 6000 6500 7000 overtonefrequency (cm-r) There is considerablevariation in the principal OH- stretching spectra of vesuvianite, more so than any Frc. 18.Variation in anharmonicity(o'/2oF) as a functionof other mineral speciesin which hydrogen is 6 major the frequency of the first hydroxyl-strerchingovertone principal bandin vesuvianite. element; the spectral features are listed below. I . There are 13 recognizablebands (A-I[) that may be divided into thrce types: (i) Eight bands (A-II) are region; the position andanharmonicity factor ofthis K polarized,with intensitiesE ll c = 8,E L c = 2; theseare band are listed in Table 4. As shown in Figure 18, due to principal OH-strerchingabsorptions at the OH the anharmonicityratio correlatesfairly well with the site. (ii) One band (4 is polarizedwith E I c = 10; this frequency of the overtone bandofurther supporting behavior is not compatible with the assignmentof the assignmentof K' as first overtoneof OH. this band to a simple OH-stretchingvibration in the The O-H interactionis quite anharmonic,the longer structure; the origin of this band will be discussed O-H bondscorrelating with increasingalharmonicity. elsewhere.(iii) Four bands ("I-M) are polarized with Longer O-H bonds also correlate with decreasing E ll c = 10; theseare due to absorptionat the O(10) principal+trerching frequency. Consequently,as the site. principal-stretching frequency decreases,the anhar- 2. The eight bands A-Il are due to different local monicity should increase; this is exactly what is configurationsof cationsat the I(3) site, which bonds observed (Frg. 18). The band width increasesas a to OH, and to different local configurationsof anions function of frequencyfor the overtonespectra, in Jine IOH--OH- and OH--FI at adjacentOIl sites. with what is observed(Fig. 14) for the fundamental 3. The four bands J-M are due to different local bands. configurations of cations at Y(l), and to different localconfigurations of anions[OH-...O2- and OH-...F] at adjacentO(10) sites. 4. TmFlicit in points 2 and 3 is the great effect that the incorporation of fluorine has on the principal 4.0 OH-stretching spectra.Vesuvianite exhibits classical Vesvhtrib two-mode behavior in this respect,but the resultant vll O00) bandsare degeneratewith bandsin fluorine-freevesu- u. 3.0 Low@erstq$ I vianite. 5. Boron is incorporatedinto the vesuvianitestructure E z.o primarily via the substitutionB + Mg + 2H + Al, and Bllc hencehas a drasticeffect on the OH-stretchingspectra. ' 1-0 In boron-rich crystals, the four bands J-M are not Epeqr c present,indicating that hydrogenhas been completely r-- replacedin the vicinity of the O(10) site. The absolute 0.0 intensity ofthe spectrais also greatly decreasedby this 4W 3500 3@ 2500 substitution,and the relative htensities of the bands Wavenumbers(cn') A-H arealso strongly affected. detail the OH-stretch- Frc. 19. Spectraof vesuvianitev1l taken at the temperature 6. Although lacking the fine of of liquid N2; the low-frequencyundulations in the baseline ing spectra in the principal-stretching region, the away from the OH featuresare interferencefringes. overtone spectra show equally diagnostic specfial 626 TTIE CANADL{N MINERALOGIST behavior. &. -(1992b): The role of fluorine 7. The spectrain the principal OH-stretchingregion in vesuvianite:a crystal-structuresfirdy. Can, Mineral. {, extendover a very wide range(3600-3000 cm-I, or 1065-1075. evenlower), and showtwo very importantfeatures that & - (1994a):The incorporation are of generalimfortance in interpretingsuch spectra: of boron into the vesuvianitestructure. Can. Minzral. 32, (i) the band width increasessignificantly with de- 505-523. creasingband-frequency, and (ii) the band intensity is nonlinearlycorrelated with band frequency. & - (1994b): Excess Y-group cations in the crystal structure of vesuvianite. Can. ACI0{oIVI.EDGENm{Ts Mineral 32.497-5M. Rrrivts, A. (1993): The We are grateful to the Deparffnentof Mineralogy, & symmetryof vesuvianite.Can Mineral. 31, 617-635. Royal Ontario Museum,for many of the samplesused in this work. Financial support was provided by the HAwTHoRNIE,F.C. (1981): Amphibole $pectroscopy.1r1 Natural Sciencesand Engineering Research Council of Amphiboles and Other Hydrous Pyriboles- Mineralogy Canadain the form of operatinggrants to LAG and @.R. Veblen,e4.). Rev. Minzral.9A, 103-139. FCH, and by the White Rose Foundation and the National ScienceFoundation grant EAR89-16064 to HorvARD,S.A. & PnrsroN, K.D. (1989): Profile fitting of GRR. We thank the reviewers and AssociateEditor powder difFractionpallems. Rev,Mincral. 20, x7 -n5. GeorgesCalas for their helpful comments. LAGER,G.A., XlE, Q., Ross, F.K., RossMAN,G.R., ARTBRUsTB,T., Rorsr.ra, F.J. & Scrurz, A.J. (1989): RmmnccEs Crystal structure of.a P4lwrc vesuvianitefrom Tanzania !f,rica, Geol. Soc.Am., Abstr. Programs21, 4120. BRowN,I.D. (1976):On the geomenry of G-H...Ohydrogen bonds.Acta Crystallogr. L32, 24-31,. RossMAN,G.R. (1988): Vibrational spectroscopyof hydrous components.I'? SpectroscopicMethods in Mineralogy and CoDA,A., (1970): DEIA GrusrA,A. IsErn,G. &MAzzt,F. Geology @.C. Hawthome, ed.). Rev. Mineral. 18, 193- On the crystalstructue of vesuvianite.Atti Accad.Sci. 206. Torino105,63-84. Rucrc.ncr, LC., Kocr4AN,V., Wsrno% S.H. & GesE,E.J. Env,R.K., Jenrczrr, J., Ewryc,R.C., Encn, T.S., Gnoer, (1975):The crystal structuresoftlree Canadianvesuvian- L.A., CHAKoIIMAKoS,8.C., Hawrrronrln,F.C. & ites.Can. MincraL13. 15-21. RossMAN,G.R. (1993): Metamict and chemically altered -369. vesuvianite.Can. Mineral. 31, 357 SKocBy,H. & RossMAN,G.R. (1991): Theintensity of amphi- bole OH bandsin the infrared absorptionspectrum. Plryr. Frrzcunam, S., LeAvENs,P.B., RnEn{cor,D,A.L. & NBLEN, Chern.Minerals 18. 64-68. J.A. (1987): Crystal structure of a REE-bearing vesu- vianite from SanBenito County, California.Ara Mineral. Var,r,sv, J.W., PBacon,D.R., BowMaN,J.R., Essm,rE,E.J. & 72.625-628. ALARD, M.J. (1985): Crystal chemistry of a Mg-vesu- vianite and implications of phaseequilibria in the system RHEn{coLD, A.L. & l,EAvENs, P.B. (1986a): CaO-MgO-AI2O3-SiO2-H2MO2. J. Menmorph. Geol. Crystal structue of a Cu-bearing vesuvianite.An. 3, t37-153. Mineral. 71, 101,1-1014. WennsN,B.E. & Moostl D.I. (1931):The structureof vesu- & - (1986b):Crystal structureof vianite Ca16,Al4(Mg,Fe)2SieO3a(OIDa. Z. Kristallogr. 78, a ton-P$lnnc vesuvianite from Asbestos,Quebec. Are. 422432. Mineral. 7l. L483-1488. YosHrAsA,A. & Marsuvroro, T. (1986):The crystal structure GIUSFpE'rn,G. &Mez4 F. (1983):The crystal sffucturesof of vesuvianitefrom Nakatatsumine: reinvestigationof the a vesuvianitewith P4ln symmety. TschermalesMineral. cation site-populationand of the hydroxyl groups. Petrogr. Mift . 31, n7 -288. Mineral.J. 13,I-12.

GRoAr,L.A., HAWTToRNE,F.C. & ERcn, T.S. (1992a):The Received July 16, 1993, revised manuscript accepted chemistryof vesuvianite.Can. Mineral.30, 1948. October6. 1994.