THE AMERICAN MINERALOGIS'I, VOL. 49, SEPTEMBER_OCTOBER, 1964 PHASE RELATIONS BETWEEN CYMRITE, BaAlSiaOr(OH), AND CELSIAN, BaAlzSizOal Y6r.q.n6 Srn2 aNo Gnoncl C. KBNNBnv, Institute oJ Geophysics anil Planetary Physics, Uni:tersity oJ CaliJornia, Los Angeles,CatiJ. Aesrnacr The chemical reaction: celsianfsanbornite+2 quartzfwater32 cymrite, has been experimentally studied in the temperature range of 200" to 850'c. and at pressuresup to 35 kb by the simple squeezer. Hexagonal celsian forms a complete solid solution series with cymrite by substitution of Al3+ for [Si(OH)]3+ with increasing water pressure (and/or de- creasing temperature). Some interpretations of the natural occurrence of monoclinic cel- sian, cymrite and sanbornite are presented. IrttnooucttoN The potassium and barium feldspars have been studied at length in this laboratory at high temperaturesand pressures.Data on the potas- sium feldspars are appearing in a separate paper. The general relation- ships between the potassium and barium feldspars are shown in the following diagram. r:-.-----.1 IK.\rsiro"|+H,O Sanirline I I larer pressur.e I Neu.l,hase I (KSi-BaAl) Solidsolution (Hyalophaneseries) -l IlaAhSLOs :FtAt"sl,c\ l{onoclinic cclsian pressure Hexagonal celsian I I Sanidineplus water goesto a new phase,KHAISLOs.OH at high pres- sure. This new phase is an analog of cymrite and an end member of a solid solution seriesinvolving cymrite. Cymrite, in turn is part of a solid solution series of which hexagonal celsian is the other end member. r Publication 1304 Institute of Geophysics and Planetary Physics, University of Cali- fornia, Los Angeles, California. 2 Department of Earth Sciences,Saitama University, Urawa, Japan. 1407 1408 Y. SE:,KIAND G. C. KENNEDY Hexagonal celsianis the high pressure-lowtemperature poiymorph of monocliniccelsian. Monoclinic celisanis an end member of a solid solu- tion seriesof which sanidine is the other member. Cymrite was describedas forming a vein within the manganiferous ore deposit of the Benallt mine in Wales b;" Smith et al. (1949). They re- ported the resultsof their microchemicaltests and r-ray study and con- cluded that this mineral with the chemicalcomposition BaAlSirOs(OH) probably had a very simple hexagonalframework tvpe structure. Hexagonal celsian was artificially prepared by Dittler and Lasch (1930), Yoshiki and Matsumoto (1951) and Davis and Tuttle (1952). Yoshiki and Matsumoto (1951) found two modifications (a and 0) of hexagonalcelsian. Tak6uchi (1958) reexaminedthe cr1'stalstructure of thesetwo types of "hexagonalcelsian" in detail and showedthat B-"hexa- gonal" celsian,which is stablebelow 300" C., is truly orthorhombic;and a-hexagonalcelsian, which is stable above 300oC., is hexagonal(D46h). No significant differencecan be observed between the r-ray powder patterns of the a- and the B-form except peak shifts owing to lattice expansion.The similarity of r-ray patterns demonstratesthe similarity of the basicframeworks of thesetwo kinds of celsian.Neither hexagonal nor orthorhombic celsianhas beenfound in nature. X-ray powder data of natural cymrite are almost identical to those of synthesized hexagonal celsian as shown in Columns D and E in Table 1. This similarity is believedto show that these two materialshave al- most the samefundamental structure. Another kind of barium-aluminum silicate, monoclinic celsian, has been described,particularlv in manganiferousore deposits(Bauer and Palache, 1926;Larsen et al., l94l; Meier, 1939; Schaller,1929; Segnit, 1946; Spencer,1943; Vermaas, 1953; Villiers, 1951; Yoshimura, 1936, 1939).The stability relation betweenhexagonal celsian and monociinic celsianhas never been clarifi.ed. It is well known that monoclinic celsian and monoclinic potassium feldspar form a complete or partial solid solution through the mineral hyalophane,which is intermediateboth in chemicalcomposition and in phvsicalproperties (Strandmark, 1903, 1904; Taylor etol.,1934;Vermaas, 1953). The present writers have recently succeededin synthesizinga new phase,KAISiaOE'HzO, from potassiumfeldspar under high water pres- sure conditions (Seki and Kennedy, 1964).The r-ray powder patterns and unit-ceil dimensions calculated for this new phase are quite similar to those of cymrite presented by Smith et al. (1949a). In order to study the relationbetween two possibiesolid solution series: c1'mrite (BaAlSiaOs(OH))-KAlSi3Os.HzOand monoclinic celsian CYM RITE-CELS I A N RELAT ION S d.9 _o N q =- E 934e O ,h> 5 N ts Z 'a U) ^o"b.J 9 6"d.F I ix?; Itro^ @ q q q q q q @q ..! €lq I I { I EIts O N g I N d N A iF o@oN O+NH 'lE a> :$6nbE60 r<€+ooohooo. q91? e.: I ": : : SNNNd Ztl aZ EA P.Z i+ AnOO@{^tO >:i E. J4 d14 (t -l Z <lN o€Eh Y.H EA z3 2," I JN OOtsN€ 3a o€€Ne iz 27 Ei :@€r3N66 f, fr 3 39fr3 R K e = Flil r$€NNNN t4z n< o€ohND€o6 zn ^ ,)p io+N: /4 'ia 6"' @ z ! E dv c q';o qr ,e r€oo€b4oN-:e DER: 3 S 3 5 F F r+i.id.i-.iq-.; F .$e* d! - € tsr i I o:- ^l r : + ^ * lq N € "a:19 € o o o 4 4 X +ONdNN l Fl l- 98:E1393ioo-'F- F o c-o-.--=-cR59RS 1410 Y. SEKI AND G. C. KENNEDY ll '6n E -* V"e.i 9 ;";+ +l+l -i il EbE; qo fE x l. €6-Z @a "s | .q ! rqE | | =JO. I OF e 6 : -il ^l x+ x os r | 3 fr 3 "al=l I o9 di "<gE zz I z3 , NO F diN n : Y^. PeE.i 9:q"l ; i ov RREIi .hiqK vr u.E r Yv =;6ll R oo 'd; N r9:? :s= t E. i g€ ae9 h-b iltl zz =.2 NN + O ++ iO __ N1 + do -o o^ 1E ix NO O i C- N- hv rc CYMRITE-CELSIANRELA:IIONS I4II (BaAlzSizOs)-sanidine(KAlSisO8) and particularly to determine the physical conditions under which cymrite and Ba-bearing monoclinic feldspar are stable, we performed experimentalwork on the chemical reactionshown below: celsian f sanbornitel2quafizf water - 2cymrite BaAhSizOs BaSizOa SiOz HrO BaAISiaOe(OH) under wide rangesof temperatureand water pressure. In the presentpaper, the solid solution relation betweencymrite and hexagonalcelsian and the stabiiity field of monoclinic celsian will be describedand their geologicalapplications will be discussed. ExprnrltBlrrAr, TECHNTeuESAND Sr,tnrnrc Marnnrrlr,s Most of the experimentalwork in the present study was carried out in the piston-anvil,"simple squeezer,"apparatus which has already been describedin detail by Griggsand Kennedy (1956)and by Pistorius el ol. (1e60). Three kinds of starting materials were used. The first was a glass having the approximate chemical composition of cymrite. The glasswas made by heating a finely ground mixture of the following materials to 1300" C. followed by rapid quenchingin an air blast: Ba(oH)z.SHeo 51.6% by weight AlzOr.xHeO (x = 1) 9.8/6 by weight SiOr.xHrO (x :. 1) 38.5/6 by weight The second starting material was an unfired mixture of the above hydrated materials. The mixture was ground under water and dried. This procedurewas repeated8 to 10 times in order to completelyhomog- enize the mixture. The third was mixtures of (1) hexagonalcelsian, sanbornite and di- barium-trisilicate (Ba2Si3O) and (2) monoclinic celsian, sanbornite and BazSiaOa.These mixtures were prepared in the simple squeezerfrom oxide mixes having the chemical composition of cymrite. Water was added to all mixesbefore subjecting them to pressure.The pressurewas raised to the desired value before heating in order to retain the water in the sample. We failed to synthesize any cystalline phase from the glassstarting mixture even when the glasswas kept at 700oand 30 kb pressurefor 21 hours. The oxide mixture of cymrite composition, on the other hand, readily transformed into a crystalline phase assemblage.At above 500o C. crystallization of the oxide mixtures was complete within fifteen minutes. 1412 TI. SEKI AND G. C. KENNEDY Mixtures of hexagonalor monoclinic celsian,sanbornite and dibarrum- trisilicate formed from oxide mixture were used to confirm the reversi- bility of the two modifications of celsian along the boundary between the hexagonaicelsian solid solution* sanborniteI qtartz and monoclinic celsian* sanbornite* quartz fields. The products were identified chiefly bv means of r-ra1' powder pat- terns taken on a Philips diffractometer,using Cu radiation; as well as by means of the polarizing microscope.The r-rav patterns of starting ma- terials and synthesized minerai assemblagesare verl' distinctive and little difficultl' was encountered in identifying even relatively small 3 5l EIpl tl Frc. 1. Stability fieid of cymrite-celsian and their associated minerals formed by the chemical reaction of 2 cymriteicelsianf sanbornite+2 qtartz+Hzo' Numbers represent the duration (in hours) of the runs. amounts of eachphase. Quartz powder or siliconpowder was used as an internal standard,in order to measureaccuratelv the 20 CuKa valuesof diffraction peaks. RBsur-rs Figure 1 showsthe stability fields of some mineral assemblagesasso- ciated with the chemical reaction, celsian*sanbornite*2 quartzf H2O 32 cymrite. Cymrite-heragonalcelsion Column A in Table 1 shows the r-ray powder data, unit-cell dimensions, unit-cell volume and optical properties of cymrite synthesizedfrom oxide mixture of cymrite composition.These data are practically the same as those of natural cymrite (Col' D in Table 1). With decreasingpressures and/or increasingtemperatures' r-rav data and optical propertiesof the mineral having the cymrite structure grad- ually approach those of hexagonalcelsian (Cols. B, C, E and G, Table CYMRITE-CDLSIANRELATIONS 1413 1). A hexagonalmineral formed from the oxide mixture of cymrite com- position at 725oC. under water pressureol 2 kilobars and associated with sanborniteand qvartz (Col. C, Table 1) showspracticaliy the same ph.vsicalproperties as thoseof pure hexagonalcelsian synthesized under room pressurefrom an oxide mixture having the chemicalcomposition of cl.mrite and celsianglass (Cois. E, F, Table 1).