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Download the Scanned American Mineralogist, Volume 63, pages 664_676, l97g Multisyste_msanalysis of beryiliumminerar stabilities: the systemBeO-A[rOa_SiO2_H2O DoNer.n M. Bunr Department of Geology, Arizona State (Jniuersitv Tempe,Arizona8528I Abstract seven commonly associatedminerals in the systemBeo-Alror-Sior-Hro includechry- soberyl,phenakite, euclase,bertrandite, beryl, kaolinite,and qiuit . The phaserule implies that not more than six of theseminerals can coexistat an invariantpoint, and, with the addition of an aqueousphase, the associationconstitutes an (n * 4; ptrase(negative two d-egreesof freedom)multisystem. The apparentincompatibility of taotinite with phenakite allowsthe splitting of this unwieldymultisystem into two smaller(n + 3) phasemultisystems, which may belabeled (Kao) and (phe).Moiar volumedata, compuier program RrlcrroN, and naturalassemblages can then be usedto derivethe presumablystabie cJnfiguration of these multisystemson p"-minus an isothermal pHro diagram. n, p-r diagramprojected through theaqueous phase shouldhave the sametopology, and cansimilarlf be drawn. on the resultingdiagrams, three . invariant-butpoinis rabeled tchrl, tBr;;, and [etz] arestable in the.multisystem (Kao), and threedistinct identically-fuU"i.Opoint, u.. stablein rhe multisystem(Phe). An implicationof this topologyvia ihe "r.tu.tubl"-rtable correspon- dence,"is that the assemblagephenakite + euclase* beryl(* aqueousphase) has a finite i'I;ix, ii,l'J.?lT"t' ::ff,,,j :r;: :":.T' ? ts why" euclase is muchrarer than bertrandite. and its stabilityfield, especially in the presence p t low and T. Most reactionsinvolving the bly occur at temperaturestoo low for conve_ 0.c). Introduction The present paper representsa first attempt to derivethe topology of the stability fieldsof these berylliumminerals. The derivationdepends on natu- ral assemblages(cf. Beus, 1960; Vlasov, 1966: Burnol. t968; Cerny, t963), Fortran program RrncrroN (Fingerand Burt, 1972),molar volume data (Robie el al., 1967),and multisystemsanalysis (Korzhinskii, 1957).Reliable thermochemical or experimentaldata on mostof the phasesare lacking, so that the results areofnecessity topological rather than quantitative. Many of the resultswere collectivelyderived as a laboratoryassignment by my springterm 1977class in ore deposits at Arizona State University. The method, heresummarized in advance,consisted bas- icallyof the followingfive steps: (l) Thesystem BeO- AlrOs-SiOr-HrOwas searched for all possiblephases that occur as mineralsor that havebeen synthesized. A numberof thesephases were eliminated from con- 0o03-004x/ 7 8 /0708_0664$02. 00 664 BURT:BERYLLIUM MINERAL STABILITIES 66s sideration,leaving seven minerals plus an aqueous Table 2 Abbreviations,formulas, and molar volumes* of eight in the systemBeO-Al,Og-SiOz-H,O fluid. (2) The resultingeight-phase multisystem was additionalminerals pseudoternary system by simplified to a six-phase Nee Abblev. FotEula Molar Volwe* projectingthrough HrO and by noting that phenakite ( I oules/bar) Be0 0.831 and bertranditethen plot at the samepoint. (3) An Bronellite Bro Behoite Beh Be (OH) 2.22 isothermal P,-minus pHrO diagram was plotted for 2 corundun Cor A12O3 2.558 (4) Natural assemblages this simpler multisystem. Dlaspore Dsp A1o (OH) t.776 most likely intersectionof A1(ori) 3.196 were usedto determinethe Gibbsite 3 (on) .Hro the degeneratedehydration reaction of bertranditeto Beryllite B1r BerSlo4 2 phenakitewith the multisystem.(5) The resultingP"- Andalusite AI6 Ar2sio5 PvP At2si40lo(oH) 12.83 minus pHrO diagram was transformedinto a topo- Pyrophyllire 2 logically identical schematic Pr"o-T diagram. *Data from Roble et al-. (1967) excepE for behoite and pyrophytllte. Beholi-e from x-ray data for B-Be(OH)2 ln Rosa (isOi); pvropnvrlite recalcurated fron Dav (1975)' Phases The quaternarysystem BeO-AlrOr-SiOr-HrO con- and water,mainly in channelpositions (Bakakin and tains, among others, the sevencommonly associ- Befov, 1962: Cerny, 1975; Hawthorne and Cerny, ated phaseslisted in Table l. Correspondingmolar 1977), and natural beryl and chrysoberyl may also volumes are given in joules/bar. Eight additional contain Cr3+, Fe3*, V3+, Sc3+,and other ions sub- phases have been omitted from the present study, stituting for A13+.Based on availabledata, there are largely becausethey have never been reported in as- no indicationsof major compositionalvariations in sociation with beryl (Table 2). The compositionsand naturaleuclase, bertrandite, or phenakite' assumednatural compatibilitiesof anhydrousminer- als in the system BeO-AlrOr-SiOz are shown in Fig- Review of exPerimental studies ure I (Burt, 1975a a summary of evidenceappears studiesand the follow" under the discussionof natural assemblages).Simi- This reviewof experimental have been made as larly, the compositionsand known compatibilitiesof ing review of natural occurrences in order to succinctlysumma- most phases in the system BeO-AlzOs-SiO2-H2O, complete as possible, data initiallyavailable projectedthrough excessquartz, are shown in Figure rizein oneplace the conflicting Much of this 2. The dashedlines on this figurerefer to uncertainor on the system BeO-AlzOr-SiOr-HrO. for the multisystems conflicting assemblagesvariously reported in the lit- data is seen to be unnecessary and these two sections may erature (again, consult the sectionon natural assem- analysis that follows, during a first reading without blages). therefore be skimmed In the following discussion,the phasesin Table I much lossof continuitY. system AIrOB-SiOr-HrO will be assumedto be stoichiometric.Natural beryl Phase equilibria in the (1976'1978) may contain considerablealkalis (Na, Cs, and Li) have recentlybeen summarized by Burt Table I Abbreviations. formulas, and molar volumes* of seven mineralsin the systemBeO-AlrOr-SiO,-H,O Nane Abbrev. MoIa! volune 0""1eel!eE) Chrysoberyl Ch! BeAI204 3.432 +,002 Phenakite Phe Be2si04 3.719+.004 EucIa6e Euc BeAlSioO (Ol{) 4.657+.010 Btr Be4S1207 (0H) 9.217+.050(?) Bertrandite 2 Beryl BrI Be^A1^Si.O- ^ 20,355 +.O25 J 2 OL6 A12S1205(oH) 9 .952 +.026 Kao 1 init e Kao 4 quartz Qtz si02 2.2688+.0001 *Data flom Roble et af. (1957) except for berttandite' The Cor bertrandite value vas calculated fron unit cel-I dinensions given BeO Chr by Solovreva and Belov (1951), and cited in Ross (1954). Sttghlly different unit cell dimenslons in Solov'ewa and Belov (1964) give a value of 9,177; use of densitles measured on natulal Eaterials Fig l. Moderate P and f mineral compatibilitiesdeduced for (2.60+.03) gives a value of 9.16+.10. lhe system BeO-AlrOr-SiOr, based on natural assemblages' BURT,, BERYLLIUM MINERAL STABILITIES determinedthat beryl breaksdown to chrysoberyl, phenakite, and cristobalite between 1300 and 1400.c. Studiesof beryl synthesisat high pressureswere initiatedby Wilson (1965),who reporteddirect syn- thesisof beryl from its melt at pressuresto 20 kbar. Beryl and phenakitereportedly were synthesizedby ----:115:: Takuboet al. (1971)to 20 kbar at 1600.C.The phase characterizations(or quenchingprocedures) in the abovetwo studiesare questionable(cf, Nassau, 1976) in light of the resultsof Munson(1967). His recon- naissancestudies indicated that naturalberyl breaks Hzo down to chrysoberyl,phenakite, and quartz at ap- proximately15.5 kbar and l340oCand to chrysobe- Fig. 2. Compatibilitiesamong some minerals in the system ryl, phenakite,and coesiteat 45.5kb, 1050"C.As BeO-AlrOr-SiO,-HzO, basedon natural assemblages.euartz is discussedbelow, this high p subsolidusbreakdown of assumedpresent. Dashed lines indicateuncertain or conflictins berylis consistentwith molarvolume data (Table mineralcompatibilities. I ). Studiesof the completequaternary BeO_AlzOr_ SiOr-HrO initially involvedhydrothermal syntheses and Day (1976,1978),and little needbe addedhere. of beryl and emerald.Van Valkenburgand Weir (1957)synthesized beryl between 500 and g50"C at I to 2 kbar, but reportedlyobtained phenakite plus glassabove 900"C. Wyart and Scavnicar(1957) syn- thesizedberyl between400 and 600oCat 400-1500 bars.At 600'C theyobtained beryl * chrysoberyl* assumedto be unstable at low to moderatetemper_ phenakite,and with the additionof CrrO, to replace atures.Studies of therelated binary system BeO_SiO, Al2Os,beryl * phenakitet quartz* Cr2O3.Frondel by Morgan and Hummel (1949) phenakiti revealed and Ito (1968)readily obtained beryl at 6g0oand 2 as the only intermediatephase; it melts incongru- kbar, and also synthesizedthe Sc-Fe analogueof ently.In thebinary systemBeO-HrO, Newkirk (1964) beryl(bassite), with phenakite,quartz, and hematite. dehydrated behoiteto bromelliteat l70oC, 1.3kbar Other synthesesare reviewedby Nassau(1976). and200oC, 4. I kbar,but thisreaction was not reversed. Beuse, al. (1963)studied the hydrothermalaltera- In the ternary BeO-SiOr-HrO,Bukin (1967)readily tion of berylin variousHF-bearing solutions between synthesized both bertranditeand phenakitebetween 500 and 600"C. They alteredberyl to quartz,to ber- 300 and 500oC, 720 atm, but bertranditeappeared trandite,and to bertrandite* muscovite.A similar favoredbelow 400"C. seriesof leachingexperiments was performed by Syr- The anhydrousternary BeO-AlrOr-SiO,has been omyamnikovet al. (1972).They alteredberyl to chry- soberyl* phenakiteat temperaturesabove 300"C and 500 kg/cm2(approximately 500 bar). They also leachedphenakite in alkalinesolutions to producea surfacecoating of chkalovite,NarBeSi2Ou. A synthesisstudy of the completesystem BeO_ hydrothermalsyntheses underunspecified conditions AI,OB-SiOz-HrObetween 300 and 700"C. I kbar is (500-600'C,
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