Tiabits, Crystal Forms and Gomposition of Thomsonite

Canadian Mineralogist Vol. 16, pp.487-493 (1978)

TIABITS,CRYSTAL FORMS AND GOMPOSITIONOF THOMSONITE

Wrr,r,revrS. WrsB Departnxent of Geological Sciences,University ol Calitornia, Santa Barbara, California 93106, U.S.A.

R. W. TscnenNrcH Zeolite Research.and Exploration, P, O. Box 5101, Everett, Washingtotr.98206, U.S,A,

AssrRAcr AlOa par SiOa. Cette substitution donne des thom- sonites qui approchent de la m6solite en com- The variation in the chemical composition of position. - thomsonite (Si/Al 1.0 to 1.3) resembles a solid Cfraduit par la R6daction) solution with mesolite (Si/Al - 1.5). Although these two zeolites are commonly associated, the most silica-rich thomsonite does not occur with INrrooucttoN mesolite. Blocky, complex crystals, occurring at Yellow Lake, British Columbia, as well as the type With a few notable exceptions, most zeolite thomsonite from Old Kilpatrick, Scotland and the minerals have variable compositions. The sa- blocky crystals from Vesuvius, have Si/Al ratios tions, which are exchangeable,can be expected near one. Bladed crystals of thomsonite occur ar to show some variability, but the Si/Al ratio a number of localities and in a range of sizes. The of the framework also commonly varies within Si/Al ratio ranges from about 1.05 for the coarsesr definable limits. It is clear from experimental blades to 1.13 for the finest. The third habit, the work in the synthesis of zeolites that silica variety faroelite, occurs in the form of botryoidal in the growth medium plays a major growths and waxy balls, which activity are composed of growing phase; extremely small crystals, and have the highest ob- role in the SVAI ratio of the served Si,/Al ratios (1.2 to 1.3). The small crystal for example, the Si/Al ratio in synthetic anal- size, simple crystal forms and the disorder of the cime is controlled by the composition of the crystals suggest rapid, disequilibrium growth that glassfrom which it grew (Saha 1959). has led to random replacement of AlOo with SiOn The interpretation of natural zeolites is less tetrahedra, This substitution cal$es the composition direct. However, studies of the compositions of of such thomsonite to approach that of mesolite. zeolites that have grown sequentiallyhave led to the conclusion that most natural zeolites grol r SorvruenB within a narrow range of silica activity, because Par la variation de sa composition chimique, la the Si/Al ratios vary little within a single thomsonite (si/Al - l.o e 13) ressemble i une locality: e.g., ferrierite-clinoptilolite (Wise & solution solide avec m6solite (Si/Al - 1.5). Bien Tschernich L976a) and offretite-erionite-levyne que ces deux z6olites se trouvent commun6ment (Wise & Tschernich 1976b). The greater vari- associ6es,la thomsonite Ia plus riche en silice n'est ability observed between localities is probably pas accompagn6e de m6solite. Irs cristaux com- a result of different temperatures. Variation in plexes et trapus Yellow (Colombie de Lake bri- the composition of thomsonite, however, does tannique), le_scristaux de la thomsonite type d'Old to be explained by these mechan- Kilpatrick (Ecosse) et ceux du V6suve on1-tous uo not appear rapport Si/Al voisin de l'unit6. Des cristaux de isms. For example, the Si/Al ratios of thom- thomsonite en lames se trouvent dans nombre de sonites in different habits at a single locality localit6s et en une gamme de tailles. k rapport show some variation. A common associationin Si/Al varie d'environ 1.05 pour les lames les plus the Pacific Northwest is thomsonite and meso- 6paissesb 1.13 pour le.s plus fines. La vari6t6 dite lite. The thomsonite here as in world-wide oc- faroelite repr6sente un troisibme facies, sous forme currences shows a range of Si/Al ratios (from d'agr6gats botryoides et de boules cireuses, compre- 1.0 to nearly 1.3), whereas Si/Al ratios of the petits, nant des cristaux extr6mement pour lesquels associatedmesolite are nearly constant at 1.5. le rapport Si/Al est le plus 6lev6 que I'on ob- ait By 1845 it was known that thomsonite oc- serv6 (1.2 i 1.3). La petite taille de ces cristaux, habits (IIey 1932). leurs formes gimples et les indices de d6sordre sug- cured in three different gdrent une croissance rapide, en d6s6quilibre, qui Long, radiating prisms rich in crystal forms' ss manifeste par le remplacement de t6trabdres such as,thosefound at Old Kilpatrick, Scotland, 487 488 THB CANADIAN MINERALOGIST

Frcs. 1. Scanning electron micrograph of blocky thomsonite, Yellow Lake, British Columbia. Flat face (upper left) is early-growth c face that was stopped by a calcite cover. The complex faces in the lower part of the photograph are from later growth. Length of bar, 0.1 mm. 2. Scanning electron micrograph of the complex forms of blocky thomsonite, Yellow Lake, British Columbia. Length of bar, 0.1 mm. were those upon which the original species ried out. The purpose of this paper is to explain definitions were based. Radiating clusters of the observations that (1) the smallest crystals fibrous crystals, actually blade-shaped,such as have the simplest forms, the highest silica con- those from County Antrim, Ireland, were later tent and the most disordered structure, and (2) found to be similar physically and chemically. the trend in chemical composition resembles a The waxy to fibrous botryoidal spherules, like solid solution with mesolite, a commonly as$o- those found at Nolso, Faroe Islands, and Goble, ciated mineral. Oregon, were also later equated with thomsonite. It was also recognized in 1845 that the HABITS axo Cnysrer, Fonrvrs oF THoMSoNITE botryoidal form was the richest in silica, where- Blocky as the coarse blocky crystals were the poorest. crystals with complex forms A detailed study of tlomsonite habits, chem- Thomsonite from Yellow Lake near Olalla, istry, crystal forms and association in various southern British Columbia, forms stout to localities in the Pacific Northwest has been car- elongate, pseudotetragonal prismatic crystals.

Frcs. 3. Scanning electron micrograph of bladed thomsonite from Skookumchuck Dam, Washington. Crystals are bounded by simple forms with a few vicinal faces modifying broad 6 faces. Irngth of bar, 0.1 mm. 4. Scanning electron micrographs of chabazite crystals on a cavity lining of tbomsonite, Beech Creek quarry, Grant Co., Oregon. kngth of bar,0.1 mm. HABITS AND COMPOSITION OF THOMSONITE 489

These crystals have grown in flattened vesicles several millimetres in two dimensions, but sel- in porphyritic trachyte flows. The thomsonite is dom thicker than 0.2 mm. The smaller, bladed characterized by a large number of different crystals are illustrated in Figure 3. The forms crystal forms (Tschernich & Wise, in prep.) and are simple: a, b, m and c. This habit appe,ars is the only example of this habit in the Pasific to represent fairly rapid growth from abundant Northwest. nuclei. The Yellow Lake thomsonite is associated At Point Sal thomsonite formed early and with brewsterite, mesolite, calcite and analcime, was followed by calcite and analcime, and latel and has formed crystals ranging in width from by natrolite. At Drain, Oregon, analcime crys- about 0.5 to several millimetres. In a few in- tatlized first, followed by thick cavity linings stances the growth of thomsonite was inter- (several cm) of large, bladed crystals of thom- rupted by the crystallization of calcite. The sonite. These were followed by needles of earlier generation of thomsonite is composed of mesolite, upon which are perched thomsonite simple crystals bounded by smooth a, b and m blades. Thomsonite was both preceded and fol- prism faces and a smooth c face (Fig. 1). Thom- lowed by mesolite at Skookumchuck Dam sonite not covered by calcite continued to grow (Tschernich 1972), but the sample anahzed here and developed complexly terminated crystals was followed by mesolite. (Figs. I & 2) with such forms as {101}, {502\, Thomsonite forms fine-grained cavity linings is {301}, {801} and {410}. of bladed crystals at several localities, but particularly common at the Beech Creek quar' Bladed crystals ry, Grant County, Oregon. These linings have Thomsonite from many localities in the a paleo blue-grey, opalescentappearance. The Pacific Northwest occurs as simple blades, flat- grofih surface is dull and seemsrough (Fig. 4); tened parallel to {010} and elongatedparallel the broken surface reveals crystals less than to c. In some growth sequencesthomsonite oc- 10 g,m thick, but with lengths up to 500 pm. curs in two generations. It is commonly the The crystals are generally aligned with the c first zeolite to crystallize but it also may grow axis perpendicular to the growth surface (Fig. again at a later stage. The crystals from both 5). The crystals have the simplest form" only the generations have similar sizes and habits and a, b and c faces. both are followed by mesolite crystallization. At Beech Creek there is an interesting variant Thomsonite from Drain, Oregon, Point Sal, of the simple cavity lining, in the form of long, California, and Skookumchuk Dam, Washing- composite rods with radiating sprays at their ton, are coarsely crystalline with crystals up to ends. These rods, which have lengths up to 1

Frcs. 5. Scanning electron micrograph of thomsonite crystals forming cavity lining, Beech Creek quarry, Grant Co., Oregon. Note the crystals have only a, b and c faces. A fracture through the lining forms the lower third of the photograph. Length of bar, 0.01 mm. 6. Scanning electron micrograph af thomsonite forming rodlike growths, possibly on mesolite needles, Beech Creek quarry, Grant Co., Oregon. Crystals are simple and similar to those forming the lining. kngth of bar, 0.1 mm. 7. Scanning electron micrograph of thomsonite forming balls and irregular growths on clay cavity lining, Beech Creek quarry, Grant Co., Oregon. kngth of bar, 0.1 mm. 490 TIIB CANADIAN MINERALOGIST

mm are composed of simFle crystals about I p,m thick and 10 .rrm long (Fig. 6). The rods TABIE t. 9EIE0IED AIALISES, CE!,L ColfXtsMl,, ANDCELL DI,tsnSIOF may have formed around a mesolite fibre, al- 0F vlilollg ItaBIrs oF ltolllomlE mou t$E rAclnlc NoRxmFT though we have not been able to unambigu- ously identify mesolite in the rods. Blocky !'L!€ C@Ee Clrc Ftlo f o,tryoldrl fary q?J€tala blail€ blades blarles blad@ lalls Botryoidal and irregular growths Yeliw spa-y, skffiu- ffi, s*"h g*"tr c"Jil, leho, OE. chuck'Ds 0!E. C@k, Clr@h, O!9. Smooth, waxy balls and botryoidal growths B.C. fash. O!e, Ore. occur at several localities in the Pacific North- eLo2 )5'55 77.66 38.64 40.?0 rl0.l8 n.95 4!,\9 west, specifically at Beech Creek and Goble, AL2o) 30,67 30.9+ 30'19 29.94 Solr 28.65 28'jP Oregon. This habit is similnl to the spherical cao 9,60 t2,4r 7L,28 7?.% 72.76 11.82 11.89 concretion descriptions applied to the variety 9tO6.52000000 trar0 4.10 faroelite (Faroe Islands) and the variety 3,6 5.N 4.76 4.y 4.I2 4,7) lin- KzO 0 .dl 0 0 0 0 o tonite (Grand Marais, Minnesota). The balls at Beech Creek commonlv Total 85.20 8r.18 85.4? 97.31 B?.t9 e+.9 t6,zo have k@taalet 7a AZ0, Fe, W. Ba ve &ught but @t Aet@bd.. irregular root-shaped growths protruding from their surfaces (Fig. 7). The thomsonite crystals CalL coatdts f,lth 40 ots|gen forming the balls and root-shaped growths are 9.93 L0,24 70,45 r0.61 10.65 10.85 11.0r1 10.10 9.?9 9,6? 9.4 9,t!3 8.96 less than 0.1 pm thick, and are oriented with 9.18 Ca 2.47 3,74 3.27 3:? 3:! 3'u+ 3.)9 their c axis more or less perpendicular to the 1.06 Na 2,09 2.16 ;ry $owth surfaces. .01 "'_!" ":? ":!7 ",i_a svAl ,94 L.o5 7.49 1.14 Some conclusions L,L3 1.18 l.23 Experimental work on crystal gf,owth and Col1 d.b€@1.o6 lq (t) sX1 wt-86 tO,O1 --z/ -r/ _-z/ crystal forms (Tiller 1969, Lof.gren 1974) has a tt.& r.d ,2.& v.o/ verified some of the general conclusions drawn b r3,L2 13.09 r3.W 13.V1 c 1.).23 13,20 t3.20 73.Lt! from various observations of crvstal habits. Crystals with smooth faces and numerous V Ptotu tlaksorbeg e6l eatton thotogtalhs. foms ?/t ltuufilci@t @tutaJ. fot t-tag trD''Cldt trnttee. have grown slowly from solutions with relative- y al@Jaba t&n 240 atd 204 paJ

~~jT- Scolccltc r+. . .1#.rl;td'.:,ln,lfl/lhom.onita '^ .jr_"..'...,I . t l-,!.'"1'" ! I ,rtorollte -=l- .ll ,' -, ,o' r~~

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1.2 sy'^l Frc. 8. Compositionalplot of thomsonitern various habits. Chemicaldata obtained in this study on blocky, bladed and bortyodial thomsonite are representedby squares,diamonds and circles, respectively.The numbers refer to analysesin Table 1. Other data points from Hey (1932) ,with localities indicatedby letters: old Kilpatrick, ScotlandK, other scot- tish localities J, Bohemia 3, West Patterson,New JerseyJ, Arkansas 24, Table Mountain, Colorado C, Grand Marais, Minnesota M, Goble and Ritter Hot Springs, Oregon O, Nova Scotia N, County Antrim, keland R, Faroe Islinds-F, Vesuvius,ltaty V, other Italian localities ?, Bombay Bo, variouslocalities in U.S.S.R.U, and New South Wales,Australia 17' A few other analysesthat further define the compositional range are from Yefimov et al, (1966) U', Antonin (1942) B', Tomkeieff (1934) R', and Harada et al. (1969)/n. The approximatecompositional raoges of the three habits are divided by dashedlines. The error bars indicate 17o variations expectedin the best analyses.

(Yellow Lake) have compositions close to the gests that there is a genetic relationship between ideal formula. ttte bladed crystals tend to be crystal size and silica content. It seems likely more siliceous, and botryoidal crystals (Beech that rapid growth gives rise to very small crys' Creek, Faroe islands and Minnesota; have the tals and high silica contents. There is also a highest Si contents. This correspondence sug- parallel relationship between Si content and

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THOMSONITE MESOLITE NoCo2Al5 Sis O2e' 6H2O No2Co2 Als Sie 036' I H2O Frc. 9. Comparisonof &e framework structures of thomsonite and meso' lite (Fischer & Meier 1965). Stippling represeotsAl tetrahedra. THE CANADIAN MINBRALOCIST complexity of the forms, with the simpler crys- have grown. However, it is unlikely that a high tals having the higher Si/Al ratios. At yellow silica activity in tle solutions causes thomsonite Lake the earlier crystals with simple forms (Fig. crystals to be small, becausethomsonite in this 'habit 1) have a slightly'higher Si/Al ratio than the is not followed by a zeolite richer in Si, part that grew last with complex forms. such as mesolite. Mesolite forms with or fol- Ideal thomsonite with equal amounts of Al lowing thomsonite in many localities, but in and Si develops an ordered framework struc- these casesthe thomsonite is eittrer in the form ture in which SiO* and AlOc tetrahedra alternate, of somewhat larger blades or very much larger leading to a c dimension twice that of mesolite blockn complex crystals. (Fig. 9). The aluminum avoidance principle of We conclude, therefore, that the rapidly Goldsmith & Laves (1955) states that Al-O-Al grown thomsonite, in small disordered crystals, bonds are much less stable than Si-O-Si bonds, accepts excesssilica as a result of nonequilibri- and therefore tend not to ocsur. As mentioned um growth. This excesssilica entering the chain earlier, structural disorder is characteristic of structure causes the Si/Al ratio to approach crystals that have grown rapidly. Therefore, that of mesolite. It is probable that crystalliza- disorder in the thomsonite framework is more tion of this high-Si thomsonite lowers the silica likely to involve random substitution of Si for activity of the solutions, thus inhibiting mesolite Al in the tetrahedral sites rather than random- formation. izjng the AlOa and SiO4 tetrahedra, which must generate abundant Al-O-Al bouds. AcrNowr,nncEMENTs X-Rav EvrnsNcs or Drsonosn This paper was presented at the Crystal X-ray powder patterns of thomsonite in the Growth Symposium of the Mineralogical Society various habits show small but consistent differ- of America's winter meeting in Tucson, Arizona ences. The poorer crystallinity of the botryoidal in February, L977. The presentation benefited thomsonite is reflected in somewhat broader from discussionsat that meeting and with Dr. peaks. For example, the 42O and 204 reflections James R. Boles, but the interpretations are still are easily resolvable (20(CuKa) = 30.540 and our responsibility. 30.33" respectively) in the bladed or blocky crystals, but are poorly resolved in patterns of botryoidal thomsonite. The c dimension, cal- RsrBnsNcns culated from the 204 peak, decreasesfrom about ANtoNrN,R. (1942): Researchon the mineralsand 13.23 for Si-poor thomsonite to about A rocks of Vinatick6 lJ:ill. Ceska SpolecnostNauk 13.15 A for the (Goble more siliceous ones Trida Matlt.-Prirodovedecka Yest. 2. sample, #7, Table l). Because ordering gives rise to a doubled c FISCHER,K. F. & METER,W. M. (1965): Kristall- dimension (Fig. 9), disordering will cause lzlc/ chemie der Zeolithe (eine Zusammenfassung reflections having / odd to diminish in intensity. neuerer Ergebnisse).Fortschr. Mineral. 42, 50- For example, the diffractometer peak at 2O.4o, 86. composed of reflections from the 221,122, and Gorosrvnr4 J. R. & Levrs, F. (1955): Cation order 212 planes, has less than half the intensity in anorthite (CaAlrSirOB)as revealed by gallium (relative to 200) in the botryoidal thomsonite and germaniumsubstitutions, Z. Krist. L06,213- than in the blocky crystals. This intensity loss is 226. primarily a result of the intensity of. the 22I HARADA,K., Urvreoe,M., Nereo, K. & Neclsruue, reflection reducing nearly to zero. K. (1969): Laumontite, heulandite and thom- sonites in altered basaltic and andesitic rocks in Corvcr.usroNs Japan.J. Geol. Soc. lapan 75, 557-552, HEy, M. H. (1932): Studieson the zeolites.II. The evidence presented indicates that the Thomsonite (including faroelite) and gonnardite. botryoidal and spherical habits of thomsonite Mineral. Mag, 23, 5l-125. are cornposed of very small, morphologically simple crystals. Moreoveq these same crystals LorcnrN, G. (1974): An experimental study of have highsl Si contents than the larger crystals plagioclase crystal morphology: isothermal crys- and show disorder effects in X-ray diffracto- tallization. Amer, l, Sci. 274, 243-273. meter patterns. Increases in silica contents of RUcKLTDGE,J. C. & G,espenFJNI,E. L. (1969): many zeolites are commonly a result of high Electron microprobe analytical data reduction- silica activities in the solution from which thev EMPADR Yfr, Dep. Geol,, Univ, Toronto,