American Mineralogist, Volume 76, pages 611-616, 1991

Experimental study of Li-rich granitic :Part II. * albite * quartz equilibrium M,rnrrNn Llcncrrr' ANsorr Snn.qsrrlx Laboratoire de G6ologie, Ecole Normale Sup6rieure,URA 1316, 24 rue Lhomond, Paris 7523l,France

Ansrntcr Spodumeneis one of the principal sourcesof Li and the most important Li in pegmatites.Experiments have been carried out at 450 "C and 600'C at 4 kbar and 750 "C at 1.5 kbar to study the equilibrium between spodumene,albite, quartz, and the co- existing hydrothermal chloride solution. Solid-solution formation in spodumene as well as in albite is very much restricted. When spodumenecoexists with albite and quartz, the alkali composition of the fluid is buffered.The value of the ratio Na/(Na + Li) of the fluid 'C, has been determined to be 0.550 + 0.020 at 450 "C, and 0.485 + 0.025 at 600 conditions at which the stableform of spodumeneis a spodumene.At 7 50"C, 1.5 kbar, the stable form is the high-temperaturepolymorph B spodumene.In the presenceof an excess of quartz, the assemblagealbite * B spodumenepartially melts from Ab30-Sp70 to Ab75- Sp25. The value of the ratio Na/(Na + Li) in the fluid buffered by coexisting albite and spodumene, with or without melt, is constant and has been determined to be 0.510 + 0.020at 750 "C.

Inrnooucrrox symmerry and is isostructural with g quartz(Li and Pea- Spodumene is the most abundant Li mineral in peg- cor, 1968b; Ioffe and Zonn, 1970). The polymorphic matites and is considered to be primary when formed transformations among the a, B, and 7 forms are recon- during the pegmatitic period of crystallization. A second structive. Beta spodumeneand 7 spodumeneare absent generation of spodumenethat crystallized during a later in nature; however, virgilite, which is a pneumatolytic period of mineralization is also known. between ,y spodumene and B qtnrtz, has been found in Primary spodumeneis found in a variety of occurrences: the Macusani volcanic , Peru (French et al., 1978; (l) as phenocrystsin poorly zoned pegmatites,(2) as a London, 1987; London et al., 1989).The absenceof B constituent of one or more zones,principally intermedi- spodumenein nature indicates that the temperaturemust ate zonesand cores,(3) rarely, as constituentsin replace- have remained below the transition temperature ofa to oC, ment units, and (4) as fillings in vugs (Heinrich, 1975; B [550-630 at pressuresof approximately0.35 to 3.1 London and Burt, 1982b).In coresit has beenfound as kbar, as determined by Edgar (1968)1.Stewart (1978), giant crystals(e.9.,2 m thick and 13 m long at the Etta London and Burt (1982a),and London (1984)place the mine, South Dakota). It occurs in some and has limit of the decomposition of petalite to 0 spodumeneat been reported in a few gneisses(Deer et al., 1978). Spod- a temperature around 680 "C and pressurebelow 4 kbar. umene is commonly associatedwith quartz, ,mi- The transition of a to B is monotropic, and Edgar (1968) cas, and minor accessoryminerals such as beryl in gra- found that, at atmospheric pressure,the inversion tem- nitic pegmatites (Gabriel et al., 1942). Spodumene can perature is between 530 and 550 .C. have high Fe3+contents, since its pyroxene structure can Alpha spodumene has proved difficult to form syn- accommodateup to 1.6 wto/oof FerO. (Heinrich, 1975). thetically(Barrer and White, l95t; Drysdale,1975; Gra- The substitutionof small amountsof Fe3+for Al3* mark- ham, 1975;Isaacsand Roy, 1958;Munoz, 1969;Roy and edly increasesthe stability of spodumene(Appleman and Osborn, 1949; Roy et al., 1950) but is very common in Stewart, 1968). Secondary spodumene produced by the nature and has been reported in many pegmatitedeposits breakdown of petalite is relatively pure (Quensel, 1938; without the presenceof either petalite or (Mu- Cernf and Ferguson, 1972; Chang, 1974). noz, l97l; Stewart, 1978).The a spodumenestructure is There are three polymorphs of the compound LiAl- very dense (specificgravity : 3.2) with Al in sixfold co- SirOu, a spodurnenobeing the only naturally occurring ordination. Synthesisunder geologically realistic condi- low-temperature stable form with a monoclinic pyroxene tions requires nucleation and growth of this densephase, structure. At high temperature,LiAlSirO5 can exist in the where these processesare slow. Several lower density form of two stuffed derivatives of silica. Beta spodumene phases(specific gravity : 2.4)l1ke B spodumene,petalite, is a high-temp€ratwe tetragonal form, isostructural with a and B eucryptite, eachwith Al in fourfold coordination, the silica polymorph keatite (Li and Peacor,1968a; Clarke can easily grow metastably (Drysdale, 1975). The pro- and Spink, 1969). Gamma spodumene has hexagonal posed instability of a spodumene at low pressures 0003-o04x/91/0304461l$02.00 611 6r2 LAGACHE AND SEBASTIAN: Li-RICH GRANITIC PEGMATITES

TABLE1. Chemicalcomposition of spodumene

o/o o/o % SiO, 7o Al,O3 Li2O % NarO 7" K2O Fe"O" "h CaO % MgO % Rbro % MnO Total 65.75 7.43 0.34 0.06 100.375

(Shternbergetal.,1912; Edgar,1968; London, 1984)pre- Becauseof these difficulties of crystallization, natural cludes its crystallization in shallow, low-pressure envi- a spodumenefrom Minas Gerais, Brazll, was used in the ronments. experiments. Its composition is given in Table l. The In a previouspaper (Sebastian and Lagache,1991), we natural spodumenewas finely powdered in an agatemor- have reviewed the experimental work conducted so far tar. Varying amounts of a mechanical mixture of the on the stability fields of lithium aluminosilicatesand pre- powdered spodumene and natural quartz or albite gel were sented new experimental results on the petalite + albite weighed in Au tubes to which varying volumes of alkali + quartz equilibrium. This work deals with similar ex- chloride solutions (l tr4) were added. The tubes were perimental studies on the spodumene + albite + qt:arrtz welded at both ends. Some experimentswere performed equilibrium to determine the composition of Na and Li with a mixture of I mol of natural spodumene, I mol of in the hydrothermal fluid that is in equilibrium with this albite gel, and quartz. For the experimentsfrom the albite assemblage.This work has been undertaken in order to end-member, 2 mg of natural spodumenewere added to understand the whole system, including (Na-Li) alumi- the albite gel as nuclei to facilitate the reverse reaction. nosilicatesand coexisting hydrothermal fluids at temper- Natural low albite was used in some experimentsinstead aturesranging from 450 to 750 "C and pressuresof 1.5 ofalbite gel. kbar and 4 kbar. Estimates of the conditions of fluid-inclusion entrap- Experimental procedure ment generally place the formation of primary spodu- The experimentsat 750'C, 1.5 kbar, were conducted mene in the range of 500 to 600 oC and 3 to 5 kbar in a Bridgman-type pressurevessel, which was partially (Bazarovand Motorina, 1969 Taylor et al., 1979;Lon- filled with HrO in order to reach the required pressure don, 1986).Accordingto Sheshulin(from Heinrich, 1975), (seeSebastian and Lagache,1991). The experimentsat the homogenization temperaturesof the fluid inclusions 450 and 600 "C, 4 kbar, were performed in a modified were 500 to 650 "C for the primary spodumene and 290 Bridgman-type pressurevessel. The required HrO pres- to 390'C for the secondaryspodumene. We have carried sure was maintained within the pressurevessel by exter- out our experiments on a spodumeneat 450 and 600 "C nally applying pressure using a pump connected to a and 4 kbar. Experiments on B spodumenehave been per- Bourdon-tube pressure gauge. The temperature was formed at 750 "C and 1.5 kbar. maintained within +2'C by chromelalurnel thermocou- As in the previous studies (Sebastianand Lagache, I 990, ples. l99l), the hydrothermal fluid is a chloride solution, even The duration of the experimentswas 30 or 80 d at 450 though the most important anions in such pegmatitic sys- "C, 12 or l8 d at 600 'C, and 18 d aI 750 oC.The ana- tems are considered to be B, F, and P (London et al., lytical procedure and the precision of the results are the 1989). Further studies will be necessaryto reproduce a same as in the previous paper on the petalite + albite bulk composition compatible with natural observations equilibrium (Sebastianand Lagache,l99l). (London, 1987). The equilibrium studied here is LiAlSirO6 + SiO, + Na* + NaAlSi3Os + Li*. The principle is similar to the Rrsur,rs one discussedearlier for petalite (Sebastianand Lagache, The resultsare presentedin Tables2,3, and 4. Xis the l99l), i.e., at equilibrium, the ratio of activities of Nat mole fraction of Na in the bulk solid assemblage,exclud- and Li* in solution is a function of the temperature,pres- ing quartz, and I is the mole fraction of Na in the solu- sure, and composition of the solid phase. tion. Graphical representationis shown by the classical isotherm-isobar distribution diagrams (Fig. la-lc) in ExpnnrunNTAL pRocEDUR-E which the composition of the solid is plotted againstthat Starting material of the solution and expressedas the ratio Na/(Na + Li), Gels of spodumene and albite were prepared by the which varies from 0 to l. Calculationsare made for solids classicalgelling method (Hamilton and Henderson, 1968). in micromoles ArM) for 100 mg and for solutions in mi- The chemical composition of the gelswas verified by wet cromoles per 100 microliters (pL). chemical analysis. From the pure spodumenegel at 450 Two sets of experiments conducted for different dura- 'C or 600 and 4 kbar, petalite and a eucryptite crystal- tions at 450 and 600 "C, 4 kbar, led to similar composi- lized instead of a spodumene.However, at 600 'C and 4 tions ofsolutions and solids,indicating that a steadystate kbar, when starting with a mixture of spodumene gel, was attained. In all of the experiments, the duration of quartz, and NaCl solution, it was possible to crystallize the experiments was sufficient to obtain equilibrium in a spodumene,albite, and quartz. the forward and reversedirections. as shown bv the con- LAGACHE AND SEBASTIAN: Li-RICH GRANITIC PEGMATITES 613

450"C 4 kbor 6OO'C 4 kbor 75OoC l.5kbor , to , to ,

c C o o = = f o o q @ a ) 7 z o z = z z z. I I I o o5 to ev * No / (No + Li ) solid Ab Sp *No/(No+Li)solid Ab Sp * No/(No+Li)solid Ab b c qC qC Fig. l. Isothermal, isobaric distribution curves at a50 (a), 600 "C O), and 750 (c). Slanting lines connect the starting assemblageand final assemblagefor an individual experiment.The solid circlesrepresent Sp + Q or Ab and empty circles represent (Sp + Q + Ab). The diamonds representthe partially molten final assemblage.

necting lines between the initial nonequilibrium assem- buffers the solution composition (ts) which remains con- blagesand the final equilibrium assemblages(Fig. la-lc). stant. The I valuesvary between450 and 600 .C: I: In Figure l, the system is bivariant along AB and CD. 0.550 + 0.020at 450 "C, 4 kbar and Y: 0.485 + 0.025 .C There is only restricted solid solution along AB and CD. at 600 "C, 4 kbar. The solutions are more sodic at 450 In both a and B spodumene,the ratio Na/(Na * Li) never than at 600'C. exceeds0.01, irrespectiveof the different structuralforms. In albite, the maximum ratio Lil(Na + Li) is also ap- DrscussroN proximately 0.01, as in earlier studies(Sebastian and La- The albite that crystallizes in the experiments per- gache,199 l). The compositionsof the solid solutionswere formed with gels and the albite that crystallizesfrom the not directly determined but were estimated by the posi- transformation of spodumene + quartz is always of the tion of points B and C. The horizontal section of the high-temperatureform (Sebastianand Lagache,I 990 and isotherm BC representsa univariant system,along which I 99 I ). Experimentsperformed with natural low albite in- spodumene saturated with Na, albite saturated with Li, stead of gels led to comparable results at all three tem- and quartz coexist in equilibrium with the fluid. Along peratures;however, the superimposition of the XRD peaks BC, the composition of the mechanical mixture of the of albite and spodumenedid not permit identification of solid phases (X) varies, and the trimineral assemblage the structural form of the albite at the end of the exper-

Tmle 2. Resultsof experimentsat 450'C, 4 kbar

Reactants Final bulk solid composition Solutioncomposition pMllOO mg pMl100pL Num- ber Days Solid mg NaOl 13 33 80 Sp+Q 100 + Sp+Q 0.30 Licl 38 34 80 Sp+Q 100 Nacl 25 Sp+O+Ab 14 361 0.04 52 44 0.54 35 80 Sp+O 50 NaCl 50 Sp+O+Ab 47 331 0.14 54 44 0.55 36 30 Sp+Q 50 Naol 50 Sp+O+Ab 42 286 0.13 54 44 0.55 37 80 Sp+Q 50 Nacl 100 Sp+Q+Ab 90 250 o.27 50 42 0.54 38 80 Sp+o 50 Nacl 200 Sp+Q+Ab 155 217 0.42 55 43 0.56 39 80 Sp+O+Ab 50 Nacl 50 Sp+Q+Ab 2',t5 137 0.61 50 42 0.54 40 30 Sp+Q+Ab' 50 Nacl 50 Sp+Q+Ab 228 146 0.61 52 44 0.54 41 80 Ab + 2mgsp 50 Licl 100 Sp+Q+Ab 260 135 0.66 s0 44 0.53 42 80 Sp+Q+Ab 50 NaCl 100 Sp+O+Ab 272 80 o.77 56 42 0.57 43 80 Ab + 2mgsp 50 Licl 50 Sp+O+Ab 311 56 0.85 52 48 0.52 44 80 Sp+Q+Ab 50 Naol 200 sp+O+Ab 330 41 0.89 55 41 0.57 NaCl 25 45 80 Ab + 2mgsp 50 + Sp+O+Ab 316 23 Licl 25 Nofe.-Reactants:Sp: 1"1rt", o spodumene,Q: quartz, Ab: albite gel, Ab. : natural low albite. Final bulk solid composition: Sp: a spodumene, Q : quartz, Ab : high albite. 6r4 LAGACHE AND SEBASTIAN: Li-RICH GRANITIC PEGMATITES

Tmu 3. Resultsof experimentsat 600 "C, 4 kbar

Reactants Final bulk solid composition Solution composition pMl100mg pMl100pL Num- ber Days Solid mg Solution Nacl 13 46 18 Sp+Q 100 + Sp+Q 366 0.01 0.26 Licl 38 47 18 Sp+Q 100 Nacl 25 Sp+O+Ab 16 354 0.04 50 54 0.48 48 18 Sp"+O 50 Naol 50 Sp+Q+Ab 56 290 0.16 44 s2 0.46 49 12 Sp+Q 50 NaCl 50 sp+o+Ab 51 241 0.18 48 52 0.48 50 18 Sp-- + O 50 NaCl '12 100 Sp+Q+Ab 113 240 0.32 45 52 0.46 51 Sp+Q 50 Naol 100 Sp+Q+Ab 110 225 0.33 48 48 0.50 52 18 Ab + 2mgsp 50 ucl 200 Sp+Q+Ab 160 218 o.42 44 52 0.46 53 18 Sp+O 50 Nacl 200 sp+Q+Ab 183 216 0.46 47 47 0.50 54 12 Sp+Q+Ab' 50 Nacl 50 Sp+O+Ab 233 128 0.65 46 48 0.49 55 18 Sp+O+Ab 50 Naol 50 Sp+O+Ab 225 115 0.66 45 50 0.47 56 18 Ab + 2mgsp 50 Licl 100 Sp+Q+Ab 265 110 0.70 45 50 0.47 .I 12 Sp+Q+Ab '12 50 Nacl 100 Sp+Q+Ab 240 60 0.80 48 48 0.50 58 Ab + 2mgSp 50 Licl 50 Sp+Q+Ab 326 51 0.87 51 49 0.51 NaCl 25 59 18 Ab + 2mgsp 50 + Sp+Q+Ab 268 22 0.92 45 50 o.47 Licl 25 60 18 Sp+Q+Ab 50 Nacl 200 Sp+Q+Ab 245 15 0.94 53 47 0.53 /Vote.'Reactants:Sp:naturalaspodumene,Sp--:spodumenegel,Q:quartz,Ab:albitegel,Ab.:naturallowalbite.Finalbulksolidcomposition: Sp : a spodumene,Q : quartz, Ab : high albite. iment. The two experimentsperformed with spodumene in the starting assemblageand in the product assemblage. gel also led to chemical equilibria similar to those ob- The studies on phase-equilibrium relations at high tem- tained with natural spodumene. perature in the systemLiAlSiO4-SiO, (Hatch, 1943; Skin- At 750 "C, 1.5 kbar, the natural a spodumeneinverts ner and Evans, 1960;Munoz,1969; Stewart,1978; Lon- to the B form. In the reverse reactions with albite and don, 1984) have shown that B spodumeneforms a series LiCl solution, B spodumene is formed, which confinns of solid solutions with keatite, a high-temperature poly- that the reaction is monotropic, as observed by Edgar morph of silica. The deficiency of quartz in the product (1968).The Ivalue is 0.510 + 0.020.In the experimenrs assemblagemay be explained by the presenceof highly where no melting appears,we observethat there is a de- siliceousB spodumene-keatitesolid solution. ficiency of quartz in the product assemblageby compar- At 750 "C, 1.5 kbar, when quartz is presentin the start- ing the relative intensities ofdiffraction peaks for quartz ing assemblage,melting is observed from XRD patterns

TABLE4. Resultsof experimentsat 750.C, 1.5kbar

Reactants Final bulk solid composition Solution composition pMflo0 mg pMl100pL Num- ber Days Solid mg Solution M pL Na

I NaCl 13 61 18 Sp+Q 100{ + BSp+Q I Licl 38 62 18 Sp+Q 100 NaCl 50 Bsp+o+Ab 23 313 0.07 s0 42 0.54 63 18 Sp+2Q 50 NaCl 50 BSp+Q+Ab JC 260 0.18 50 51 0.50 64 18 Sp+Ab 50 Licl 100 BSp+ O 112 316 0.26 52 46 0.53 65 18 Sp+Q 50 NaCl 100 PSp+Ab+M 97 231 0.30 46 44 0.51 66 18 Sp+20 50 NaCl 100 PSp+Ab+M 107 200 0.35 47 47 0.50 67 18 Sp+Ab 50 Licl 50 BSp+ Ab 177 255 0.41 52 48 0.52 68 18 Sp+O+Ab 100 NaCl 50 BSp+Ab+M 163 128 0.56 44 46 0.49 69 18 Sp+Q+Ab' 100 NaCl 50 BSp+Ab+M 127 103 0.55 46 48 0.49 70 18 Sp+20+Ab 50 NaCl 50 BSp+Ab+M 210 120 0.64 50 45 0.53 71 18 Ab 50 Licl 100 BSp+ Ab 258 141 0.65 50 47 0.52 72 18 Sp+2Q+Ab 50 NaCl 100 PSp+Ab+M 16ii! 74 0.69 50 42 0.54 73 18 sp+Q+Ab 50 NaCl 100 BSp+Ab+M 178 63 0.74 45 51 0.49 74 18 Ab 50 Licl 50 PSp+ Ab 320 45 0.88 47 48 0.50 75 18 Ab 100 Licl 50 PSp+ Ab 325 24 0.93 54 50 0.52 /o 18 Sp+Q+Ab 50 NaCl 200 Ab 340 5 0.99 58 40 0.59 I NaCl 25 77 18 Ab 100J + Ab 350 5 0.99 o.57 I LiCt 25 Note:Reactants:Sp:naturalaspodumene,O:quartz,Ab:albitegel,Ab-:naturallowalbite-Finalbulksolidcomposition:PSp:Bspodumene, Q : quartz, Ab : high albite, M : melt. LAGACHE AND SEBASTIAN: Li-RICH GRANITIC PEGMATITES 615 where0.30 < Na/(Na + Li) < 0.75 in the bulk (solid + RnrnnrNcns crrED melt). For compositions with Na/(Na + Li) equal to 0.55, the assemblageis almost completely molten. This is in Appleman, D.E., and Stewart, D.B. (1968) Crystal chernistry of spodu- pyroxenes. (abs.) America Special good with liquidus mene-type Geological Society of agreement the diagram of the system Paper,l0l,5-6. albite-eucryptite-quartz determined by Stewart (1978). Barrer, R.M., and White, E.A.D. (1951) The hydrothermal chemistry of This phenomenon is not observed in experiments with- silicates. Part I. Synthetic lithiurn aluminosilicates. Journal of the out quartz in the starting assemblages,where there are Chemical Society,Iondon, 283, 1267-1278. 4lo/o and 65 molo/oof albite in the final product assem- Bazarov, L.S., and Motorina, I.V. (1969) Physico-chemicalconditions during formation of rare-metal of the -rich type. blages. Doklady Akademii Nauk SSSR,Earth Science Sections, I I 8, 124-126. We can assumethat the melt presentduring the exper- Carron, J.P., and lagache, M. (1980) Etude expdrirnentaledu fractionne- iments contains approximately 4-5o/o dissolved HrO ment des 6l6mentsRb, Cs, Sr et Ba entre feldspathsalcalins, solutions (London et al., 1988).This correspondsto a maximum hydrothermales et liquides silicat6s dans le systdme Q-Ab-Or-H'O n 2 qc. Bulletin Min6rologie, 130, 571-578. of l0o/o fluid presentin kbar, entre 700 et 800 de of the experiments68 and 69,5o/o Cernj, P., and Ferguson,R.B. (1972) Petalite and spodumenerelations. in experiment70, and 2.5o/oinexperiments 72 and,73,if Canadian Mineralogist, ll, 660-678. all the final product assemblagesare supposedto be melt. Chang,J.P. (1974) Preliminary study of a spodumenepegmatite in China The amount of solution is then reduced, and its concen- (in Chinese with English abstract). Geochimica, 182-191 (not seen; tration is enhanced.It has been shown many times (Or- extracted from Mineralogical Abstracts, 26, 7 5-2418, 1975). Clarke, P.T., and Spink, J.M. (1969) The of beta-spod- ville, 1963; Lagache,1984)that homovalent exchanges umene LiAlSirO;IL Zeitschrift fiir Kristallographie, l3O, 420-426. between and solution are independent of the Deer, W.A., Howie, R.A., and Zussman,J. (1978) Rock-forming miner- molality of the solution. In that particular case,we can als, vol. 24: Single-chain silicates (2nd edition) p. 527-543. Wlley, also estimate that the solubility of HrO in the melt does New York. (1975) synthesisof various spodumenes. not affect the chemical equilibrium Drysdale, D.J. Hydrothermal between the solid American Mineralogist, 60, 105-l 10. phaseand the fluid. Edgar, A.D. (1968) The alpha-beta LiAlSirO6 (spodumene)transition from It is remarkable that the ratio Y : Li/(Li + Na) in the 5000 to 45000 Iblin2 P',o. In Intemational Mineralogical Association, solution is the same whether melt is present or not, and Papen and hoceedings, 5th generalmeeting, Carnbridge, England, 1966. even when the bulk final assemblageis a melt. From ex- Mineralogical Society, London,222-231 (not seen; extracted from Mineralogical Abstracts, 19, 3, 1968, 194). perimental results (Carron and Lagache, 1980; London French, B.M., Jazek, P.A., and Appleman, D.E. (1978) Virgilite, a new et al., 1988;Webster et al., 1989),we know that there is lithium aluminosilicate mineral from the Macusani glass, Peru. Amer- little or no significant vapor-melt fractionation for alkali ican Minerafogist, 61, 461-465. elements at 7 50 'C. When the bulk solid assemblageis Gabriel, A., Slavin, M., and Carl, H.F. (1942) Minor constituentsin spod- umene, Economic Geology, t7, l\6-125. entirely molten, its composition is approximately that of Graham, J. (1975) Some notes on alpha-spodumene,LiAlSirOo. Ameri- the fluid, and the ratio Na/Li is near unity in the fluid can Mineralogist, 60, 919-923. and in the melt. Hamilton, D.L., and Henderson, C.M.B. (1968) The preparation of sili- cate compositions by a gelling method. Mineralogical Magazine, 36, 832-838. CoNcr,usroN Hatch, R.A. (1943) Phase equilibrium in the system LirO-AlrOr-SiO,. American Mineralogist, 28, 47 l-496. As we had already seenfor the petalite + albite assem- Heinrich, E.W. (1975) Economic geologyand mineralogy of petalite and blage,the composition of the solution in equilibrium with spodumene pegmatites. Indian Joumal ofEarth Sciences,2, 18-29. the assemblagespodumene (saturatedwith Na) + albite Iotre, V.A., and Zonn, Z.N. (1970) Growth of single crystals of beta- (saturatedwith Li) + quartz is not very much affectedby eucryptite and beta and gamma-spodumene.Soviet Physics-Crystal- a change in the temperature. The Na/Li ratio is lography, 15,342-343. always Isaacs,T., and Roy, R- (1958) The alpha-b€ta inversions of eucryptite near unity, as in the caseof petalite. Although the influ- and spodumene.Geochimica et CosmochimicaAcla, 15, 213-217. ence of temperature is small, it is opposite that of the Iagache, M. (1984) The exchangeequilibrium distribution ofalkali and petalite + albite equilibrium: the solution is richer in Na alkaline earth elements between and hydrothermal solutions. for the petalite + albite equilibrium at higher tempera- In W. Brown, Ed., Feldsparsand feldspathoids,p. 247-279. Reidel, Boston. tures, where it is richer in Li for the spodumene + albite Li, C.T., and Peacor,D.R. (1968a) The crystal structure of LiAlSi,O"-[ equilibrium. We discuss these results in a forthcoming (beta-spodumene). Zeirschrift fiir Kristallograpbte, 123, 46-65. paper (Dujon et al., in preparation). -(1968b) The crystal structure of LiAlSi'Ou-III (high quartz solid solution). Zeitschrift fiir Kristallographie, 127, 327-348. London, D. (1984) Experimentalphase equilibria in the systemLiAlSiOo- AcxNowr,rncMENTS SiO,-HrO: A petrogenetic grid for lithium-rich pegmatites. American Mineralogist, 69, 995- 1004. This work is part of the doctoral thesis of the second author, to whom -(1986) Magmatic-hydrothermal transition in the Tanco rare-ele- a scholarship has been granted by the French govemment. It was financed ment pegmatite: Evidence from fluid inclusions and phase-equilibrium by the Institut National des Sciencesde I'Univers, grant 883851, Dyna- experiments.American Mineralogist, 7 l, 376-39 5. mique et Bilan de la Terre, the Centre National de la Recherche Scienti- -(1987) Internal differentiation of rare-elements pegmatites: Effect fique, and the Univerrsit6 Paris VI. We wish to thank D. I-ondon and ofboron, phosphorous and fluorine, Geochimica et Cosmochimica Acta, J.D. Webster for their thorough criticisms and their fruitful comments, 51,403-420. which improved the inirial manuscript. London, D., and Burt, D.M. (1982a)Lithium-aluminosilicate occurrences 6r6 LAGACHE AND SEBASTIAN: Li-RICH GRANITIC PEGMATITES

in pegmatites and the lithium-aluminosilicate phase diagram. Ameri- Sebastian,A, and lagache, M. (1990) Experimental study ofthe equilib- can Mineralogist, 67, 483-493. rium between , albite and hydrothermal fluid in pegmatitic - (1982b) Lithium minerals in pegmatites In P. Cemj', Ed., Granitic systems.Mineralogical Magazine, 54, 447-454. pegmatitesin scienceand industry, p. 99-133. Mineralogical Associa- -(1991) Experimentalstudy of lithium-rich granitic pegnatites: Part tion ofCanada Short CourseHandbook, Winnipeg, Canada. I. Petalite + albite + quartz equilibrium. American Mineralogist, 76, London, D., Hervig, R.L., and Morgan, G.B., VI (1988) Melt-vapor sol- 205-2t0. ubilities and elementalpartitioning in peraluminousgranite-pegmatite Shternb€rg,A.A., Ivanova, T.N., and Kuznetsov, VA. (1972) Spodu- systems:Experimental results with Macusani glassat 200 MPa. Con- mene-a mineral depth indicator. Doklady Akademii Nauk SSSR,Earth tributions to Mineralogy and Petrology, 99,360-373. ScienceSections,202, lll-114, 1973. (not seen;extracted from Min- London, D., Morgan G.B. VI, and Hervig, R.L. (1989) Vapor-undersat- eralogicalAbstracts, 24, 73-1597 , 1975). urated experimentswith Macusani glass + H,O at 200 MPa and the Skinner, B.J., and Evans, H.T. (1960) Beta-spodumenesolid solutions internal differentiation of granitic pegmatites. Contributions to Min- and the join LirO-AlrOr-SiOr. American Journal of Science,258 A, eralogyand Petrology, 1O2,l-17. 312-324. Munoz, J.L. (1969) Stability relations of LiAlSirOu at high pressure.Min- Stewart, D.B. (1978) Petrogenesisof lithium-rich pegmatites.Arnerican eralogicalSociety ofAmerica SpecialPaper 2,203-2O9. Mineralogist, 63, 970-980. -(1971) Hydrothermal stability relations of synthetic lepidolite. Taylor, B.E., Foord, 8.E., and Friedrichsen,H. (1979) Stableisotope and American Mineralogist, 56, 2069-2087. fluid inclusion studies of gem-bearing granitic pegmatite- dikes, Orville, P.M. (1963) Alkali exchangebetween vapor and feldsparphases. San Diego County, Califomia. Contribution to Mineralogy and Petrol- American Journal of Science.261. 201-237. ogy,68, 187-205. Quensel,P. (1938) Minerals of the Varutrask pegmatite.X. Spodumene Webster, J.D., Holloway, J.R., and Hervig, R.L. (1989) Partitioning of and its alteration products. Geologiska Foreningen i Stockholm For- lithophile elements between HrO and HrO + CO, fluids and topaz handlingar, 60, 201-21 5. rhyolite melt. Economic Geology, 84, I l6-134. Roy, R., and Osborn, E.F. (1949) The systemlirhium metasilicate-spod- umene-silica.Journal ofAmerican Chemical Society, 71, 2086-2095. Roy, R., Roy, D.M., and Osborn, E.F. (1950)Compositional and stability relationships among the lithium alumino-silicates:Eucryptite, spodu- Memrscnrrr REcETvEDApnlr 18, 1990 mene,petalite. Journal ofthe American Ceramic Society,33, 152-159. MaNuscrrpr AccEprEDDecer*,rspR. 21, 1990