Introduction

The composition of trioctahedral brittle micas canbe represented by the simplified general formula

Ca(Mg,Fe'+,Fea+,Al)r(Al,Si)rO,o(OH,F,O)r.

Although not very common, they are of generalmineralogical and petrological interest because theyoccur in thermally metamorphosed calcium- andaluminum-rich rocks. What makes this group in-triguing from the view of crystal chemistry is theirhigh proportion of aluminum in tetrahedral sites.Some rare mineral species such as bityite (=bowleite), anandite, and ephesite are structurallyrelated to the trioctahedral brittle micas, but incor-porate larger amounts of cations such as Li, Be, Ba,Na, and Fe2+ so as to be chemically distinct fromxanthophyll ite, clintonite, and brandisite, the morecommon rock-forming trioctahedral calcium micas.A survey of the reported analyses for brittle micasshowed that the cations Ca, Mg, Al, and Si arepredominant, iron oxide (total iron) amounting to atmost 3.5 wt percent, NarO to at most 1.9 wt percent,and all other oxides being less than 0.7 wt percent.The chemical composition of trioctahedral calciummicas can thus be closely represented in the systemCaO-M gO-AlrOs-SiO,-HrO.

American Mineralogist, Volume 60, pages 188-199, 1975

From the many names of so-called varieties oftrioctahedral calcium micas (Hintze, 1897) the termsbrandisite, clintonite (seybertite), and xanthophyllitehave been widely used. However, Tschermak andSipdcz (1879) pointed out that the name clintoniteshould be used exclusively, because the variability inchemical composition and physical properties withinthis group is very small and does not warrant distinc-tion of several mineral species. This latter statementhas been supported by further chemical (Koch, 1935)and structural (Forman et al, 1967a,b) investigations.For a thorough discussion of nomenclature of trioc-tahedral calcium micas the interested reader isreferred to the compilation in Olesch (1973). In thepresent paper the name clintonite will be used ex-clusively for the entire group of trioctahedral calciummicas represented by the above general formula.

Previous syritheses of trioctahedral calcium micashave been mentioned by Roy and Tuttle (1961; un-published results of De Vries and Roy, 1954) andChristophe-Michel-L6vy (1964). Some data on solidsolubility are given by Velde (1973). The presentpaper reports the results of synthesis experiments as afunction of temperature, water pressure, and bulkcomposition. The data were used to determine thelimits of solid solubility and some physical propertiesof the mica phases.

Synthesis and Solid Solubility of Trioctahedral BrittleMicas in the System CaO-MgO-AlrOs-SiO2-H2O

Mnnrn Ornscs

Mineralogisches Institut der Uniuersitiit Kiel,2300 Kiel, Olshausenstrasse 40/60, Germany

Abstract

Single-phase trioctahedral brittle micas (clintonite, xanthophyllite, brandisite) of compositionsca(Mgr*,Alr-'XAl.-,si,oroxoH), with z from 0.6 to 1.4 were synthesized on the join cao:3Mgo:Alror:2SiO, + xHrO-CaO:MgO: 3AlrO, * xHrO (substitution AlIv + Alvr : MgSi) at 600-g70" at 2 kbarwater pressure. The ca analog of phlogopite, i.e., caMgr(Alrslor)(oH), could not be synthesized. solidsolubility of the trioctahedral towards dioctahedral calcium micas (e.g., margarite) was studied on twojoins starting with z : l.l7 and z : 1.o. These two joins involve the compositions ca(Mgo u-*Al"-o rr)(Al4-,Si,O,oXOH), and Ca(Mg._r,Al")(Al.-,Si.Or0XOH), (substitution 2Mg + AlIv : Alvr + Si),respectively. Maximum solid solubility towards the dioctahedral component on these joins wasfound to be l0 mole percent (1.17 < z < 1.27) and 24 mole percent (1.0 < z < 1.24), respectively.

All mrcas synthesized were of the I M (or 3 I) polymorphic type. Their lattice constants a, b, c, Vdecrease with decreasing z in the strictly trioctahedral micas and also with increasing dioctahedral compo-nent' B remains constant. The solid solubility encompasses and, on the alumina-rich side, even exceedsihevar iat ion in natural calc ium micas.

r88

SYNTHESIS AND SOLID SOLUBILITY OF TRIOCTAHEDRAL BRITTLE MICAS 1 8 9

Experimental Methods

High Pressure-High Temperature Apparalus

Synthesis runs were performed in cold sealautoclaves and in an internally-heated gas apparatus.The cold-seal pressure vessels were similar in designand dimensions to those described by Luth and Tut-tle ( 1963). Water pressure was continuouslymonitored by Bourdon gauges, and the precision ofthe pressures reported is t5 percent at pressures of 2kbar and below, and 12 percent at higher pressures.Temperatures were controlled and measured throughchromel-alumel thermocouples calibrated against themelting points of NaCl (800.5'C) and zinc (419.5'C).To avoid error by contamination and/or re-crystallization, the thermocouples were changed afterevery run above 700oC. Considering all errors, theprecision of the temperatures reported is l5oC. Runsat P-T conditions above 800oC at 2 kbar and above700'C at 5 kbar were performed in an internally-heated gas apparatus as described by Seifert (1970)with uncertainties in pressure of *2 percent and intemperature of * 10"C. The pressure effect on the emfof the Pt-Pt9ORhl0 thermocouples has beenneglected.

Starting Materials

For most of the compositions investigated,dehydrated gels were prepared according to themethod described by Hamilton and Henderson(1968). Checking the chemical composition of somegels by chemical analysis yielded good agreement ofintended and determined stoichiometric ratios.However, up to 2.38 wt percent COz were found inthe gels (cf Ito and Arem, 1970). This is not sur-prising, because some water is always retained in gels,and moist finely divided Ca-bearing gels can be ex-pected to pick up CO, rapidly from the air, due totheir strongly basic reaction. Considering theamounts of gel and water used in the experiments,this CO, content corresponds to an Xs6 up to 2.2mole percent in the gas phase. The effect on theproducts of synthesis of this COz content in the start-ing material will be discussed below. Only for somecompositions within the field of solid solubility of themica phase have mixtures of gels been employed (seeTable l, section A). Although the gels used in prepar-ing gel mixtures were carefully dried for several hoursat 850oC, the chemical composition of these mixturesis less well defined because of the stil l varyingamounts of adsorbed water.

The gels were found to be optically isotropic and

Tnsls L Composition of Gels and Gel Mixtures andCorresponding Theoretical Structural Formula of Micas

O x i d e P r o p o r E i o n s

C a O : M g 0 : A 1 2 0 3 : S i 0 2

T h e o r e t i c a l M i c a F o r m u l ao n t h e B a s i s o f 2 2 C a t i o nV a l e n c i e E ( C a t i o n s o n l y )

c . Mgv r e t v r l , t l v s i rV

S e c t i o n A

24cB

5n

E6

7G8t 8

| 2 , 3 8

| 2 , 1 7

| 2 , o

| 1 . 6

i . 0

| . 6 2| , 6 7

l . 7 l

I . 8 3I Q

2 . O

2 . 12 . 2 52 . 4

2 , Ol . 7 5

| . 3 8

! , q

t . 2 51 . l 7L lt . 0

0 . 90 . 7 50 . 6o . 5o , 2 5

3 . 02 , 7 5

2 . 3 8

2 . 2 92 . 2 52 . 1 7

2 . O

, 9

- 2 . O 2 , Oo . 2 5 2 . 2 5 | . 7 50 . 5 2 , 5 1 . 5o . 6 2 2 . 6 2 | , 3 4o . 5 7 2 . 6 ' t t . 3 3

o . 7 t 2 , 1 t 1 . 2 9o . 7 5 2 . 7 5 1 , 2 50 . 8 3 2 . 8 3 I . l 70 . 9 2 . 9 l . l1 . 0 3 , o l . o

t . r 3 . 1 0 . 9t . 2 5 3 . 2 5 0 . 7 5t . 4 3 . 4 0 . 61 . 5 3 . 5 0 . 5| , 7 5 3 , ' 1 5 0 , 2 5

S e c t i o n B

9 I : 1 . 8 33 5 I | 1 . 9 2l 0 I | 2 , 03 4 I : 2 . 0 8

S e c t i o o c

I a l . I 1 1

! 0 1 . r t o

1 . 8 3 r 1 . 2 51 . 8 3 : l . 2 l

r , 8 3 r . 0 2 , 6 1 1 , 3 3| . 9 2 0 . 9 5 2 . 7 | | . 2 92 . O O . 9 2 2 . 7 5 t , 2 52 . 0 8 0 . 8 8 2 , 7 9 | . 2 1

! L O

| | , 2: L 4: 1 . 6

. l o

2 72 8? c3 03 2

3 3

| 2 . 0| 2 , O

| 2 , 0| 2 . o| 2 , O

1 . 41 . 3

1 l

I . 0 5

1 . 0

I 4L 5

r . 8l o

. ) z . ) l . )

. 4 2 , 6 t . 4l t t 1 2

. 2 2 . 8 | , 2

. 1 5 2 . 8 5 l . l 5

. t 2 . 9 l . l

. 0 5 2 . 9 5 1 . 0 5

* N u m b e r s d e s i g n a t e c o n p o s i t i o n s P r e P a r e d d i r e c t l y a g

a g e ! , v h e r e i s l e t t e r s r e P r e s e n t g e L n i x t u r e s ( c f .

t e x t ) .

amorphous to X-rays. For the runs, some 25 to 35 mgof gel and 5 to l0 mg of doubly distil led water werewelded into gold or platinum tubes, the weights beingchecked after every step of preparation and after theruns, and only tight tubes being considered.

Identification of Phases

The run products were investigated with binocularand petrographic microscopes, and by X-ray powderdiffractometry. The color of the products wasgenerally white as to be expected from the com-ponents used. Only in very long runs (of more than2000 hours duration) at temperatures below 420'Cwere some products lightly gray. No additionalphases could, however, be identified microscopicallyor by X-rays. It is tentatively concluded that the CO,present in the charge (see above) was reduced to car-bon by hydrogen that, being generated by reaction ofthe hydrous pressure medium with the bomb walls,diffused slowly into the capsules. Assuming oxygenfugacities close to the Ni-NiO buffer (Huebner,l97l), graphite is stable in a C-H-O atmosphere

190 MARTIN OLESCH

below 470oC at 2 kbar and 400.C at I kbar (Frenchand Eugster, 1965).

Because of the fine-grained nature of most runproducts, the phases were identified mainly by X-raypowder methods, using a diffractometer with Ni-filtered Cu radiation and a scanning speed of l" 20per minute. Lattice constants were determined fromdiagrams obtained with 0.25 or 0.125o 20 per minutescan speed, oscillating several times. Silicon (99.999Si, Schuchardt, Miinchen, Lot No. Si 173) served asan internal standard employing the following peakpositions (from Philips Laboratory Service Manual):I I I , 28.466" 20 CuKa; 220, 47.302" 20 CuKa; and3I l, 56.122" 20 CuKa1. Reflections below 45" 20 wercevaluated from the CuKa peaks, those at higher 20from CuKa,. Due to the platy habit of the micassome degree of preferred orientation might be ex-pected, affecting the relative intensities. However, ad-mixture of cork powder or treatment of the samplesurface according to Peters (1970) did not affect theintensities significantly. No special precautions were,therefore, taken in the preparation of X-ray samples.Lattice constants were calculated by the least-squarestechnique using the program of Burnham (1962).

Chemistry of Natural TrioctahedralCalcium Micas

All chemical analyses reported for these micas wereevaluated critically in order to obtain a guide-line forthe study in the synthetic system. Analyses madebefore the important paper by Tschermak and Sipiicz(1879) have not been considered (cf Doelter, l9l7).Similarly analyses were discarded, where only struc-tural formulae have been reported (Takeuchi andSadanaga, 1959; Akhundov, Mamedov, and Belov,l96l; Stevenson and Beck, 1965). In the remaininganalyses the sum of SiOz + Alros + MgO * CaO *H2O amounts to between 94.55 and99.9 wt percent,justifying the use of these components as a suitablemodel system. The remaining 0.1 to 5.45 wt percentare represented by (maximum values in wt percent):0.58 TiO2, 3.24 FerOr, 2.56 FeO,0.03 MnO, 0. 14 SrO,0.04 BaO, 1.86 NarO,0.58 K2O, l .9l F, 0.25 Cl,(cfanalyses mentioned in legend to Figure l).

The analyses were recalculated to mineral formulaeon the basis of22 cation valences (Stevens, 1947).Ca,Ba, Sr, K, Na were assigned to interlayer sites; Si andpart of AI were used to fill the tetrahedral positions;and all other atoms including the rest of Al were in-corporated in the octahedral positions. Figure Ishows a plot in a projection of the system CaO(* SrOt BaO * NarO + KrO) - MeO (+ FeO + MnO)

Akermqni te Anorthite

Forsterite

CorundumMgo Spinel

Molc per ccnt

MgO 12 40 38

Al2O3

2011 A1203

Mole par cent

FIc. l. Analyzed compositions of natural trioctahedral micas,projected in the model system CaO-MgO-AlrOr-SiOr-HrOthrough the CaO and HrO poles. a. The model system with the sec-tions A, B, and C investigated as well as some important mineralphases. The melilite solid solution (Mel"") extends from akermaniteto gehlenite, that of diopside (Di*) from pure diopside towardscalcium Tschermaks molecule. In this projection both gehleniteand calcium Tschermaks molecule plot at the same composition asmargarite and are, therefore, not indicated. The point labelled| :3'. l '.2 (molecular proportions CaO:MgO:AlOr:SiOr) representsthe calcium analog of phlogopite.

b. Enlarged portion of the projection. Here, the MgO-component includes the oxides MgO, FeO, and MnO; the AlrO,-component AIrOr, FerOr, and TiOr; the SiO, component only SiOr,and the CaO component CaO, SrO, BaO, NarO, and KrO.

Locations and references of analyses: la Schischimskaja Gora,Slatoust, Ural (Nikolajew, 1884). lb ibid (Koch, 1935). tcibid (Forman et al, 1967a). 2a Nikolaje-Maximilianowsk,Achmatowsk, Ural (Nikolajew, 1883). 2b ibid (Doelter,l9l7; anal.R, Schlaepfer, 1889).2c ibid (Clarke and Schneider, 1892).2d ibid(Koch, 1935). 3 Crestmore, Cal i fornia (Eakle, 1916).4a,4b MonteCostone, Adamello, Alps (Bianchi and Hieke, 1946). 5 Lago dellaVacca, Adamello, Alps (Sanero, 1940). 6a, 6b Chichibu Mine,Japan (Harada, Kodama, and Sudo, 1965).7 Amity, New York(Tschermak and Sip6cz, 1879).8 Pargas, Fin land (Lai takar i , l92l ) .9 Montezuma Valley, California (Forman et al, 1967b). lOa Toalde la Foja, Monzoni, Alps (Tschermak and Sipiicz, 1879). l0b, lOcibid (Koch, 1935').

a

36b

Si02

SYNTHESIS AND SOLID SOLUBILITY OF TRIOCTAHEDRAL BRITTLE MICAS l 9 l

- Al,O3 (* Fe,O' + TiOr) - SiO, - H,O from theCaO and HrO poles. The scatter of mica com-positions in the projection of Figure I might be ex-plained by applying crystal chemical relationshipsknown from the trioctahedral potassium micas (e.g.,phlogopite) where the amounts of sil ica, alumina,and divalent atoms (mainly Mg and Fe'+) varybecause of the (l imited) substitutions AlvI + Allv :

MgSi (phlogopite-eastonite) and 2AlvI : 3 Mgu'(phlogopite-muscovite) (Crowley and Roy, 1964).Whereas, by the first-mentioned substitution, thetotal number of atoms per formula unit remains con-stant, the latter implies formation of vacancies in theoctahedral layer, i.e., solid solubil ity towards dioc-tahedral micas. Starting from a Ca analog ofphlogopite, CaMgr(AlrSiroroXOH)r, the substitution2 Al - MgSi could lead theoretically to a trioc-tahedral end member, Ca(MgAlrXAl)4O10(OH)r,whereas the substitution 2 Al - 3 Mg could lead tomargarite, CaAL(AlrSiroloXOH)r, which is dioc-tahedral. Line A (Fig. l) represents compositionalvariations due to the first-mentioned substitution,which explains most of the variation observed. Solidsolubil ity towards dioctahedral calcium mica, asevidenced by deviations from line A, is more l imited.Although some analyses plot slightly below line A,the larger deviations are observed on the SiO, andALO, rich side of l ine A, i.e., in the direction towardsmargarite (see also Fig. 2). Thus, some linear com-bination of 2 Al : MgSi and 3 Mg : 2 Al must occurin some natural clintonites, e.g.,2Mgvt * AIIV : SiIV+ AlvI, plotted as B and C in Figure l. These twolines start from different compositions on join A.These relationships are further emphasized when the

1.0 0.8S i l v = Z

Frc. 2 Plot of tetrahedral us octahedral cations in natural clin-tonites. A. B. and C are the substitution lines investigated

Trsle 2 Results of Crit ical Synthesis Runs onSection A

C o m p o - R u ns i t i o n * N o * * ^

- H r o( " c ) r r r l . )

D u r a t i o n C o n d e n s e d P h a s e s( H o u r s ) 0 b s e r v e d * * *

7 8 6 2 0

6 3 1 2 5

3 3 4 B 7 5

3 4 8 9 2 5

3 8 1 8 6 5

4 1 0 8 9 0

4 3 ' , 6 1 5

4 1 1 8 9 0

4 1 6 0 5

3 0 0 9 0 0

3 1 0 9 0 0

1 6 9 ' 8 0 0

I 6 8 ' | 8 0 0

1 6 1 t 8 0 0

4 4 ' 6 7 5

I O O ' 8 0 0

3 9 0 8 6 5

1 4 8 6 0 0

1 7 4 ' , 8 0 0

3 1 9 9 1 5

3 3 9 ' 8 6 5

4 4 6 6 0 0

1 2 6 0 0

4 5 ' ( , 7 5

4 3 7 7 5 0

4 4 5 1 5 0

2 3 8 8 0 0

1 4 9 6 0 0

3 2 4 ' . 8 s 0

4 4 A 7 5 0

r 7 0 ' 8 0 0

3 7 1 1 5 0

3 4 r 8 1 5

5 8 8 6 9 0

1 1 1 8 0 0

3 4 2 8 1 5

5 8 9 6 9 0

3 4 3 8 1 5

c l i n . D i , F o , C cs s s s

C l i n , D i , l o , ? S Ps sC l i n . C h l , C c , ?s sC l i n . . ^ , D i ^ ^ , F o , ? S p

C l i n . D i , F o , S ps s ' 5 s

C l i n

C l i ns s

2 . O

2 . 4

2 . O

2 . 0

2 . O

2 , O

2 . O

2 , 4

5 . 0

7 . O

2 . 0

2 . O

2 . O

2 . O

2 . O

2 . O

1 . O

2 . 4

5 . 0

2 . O

2 . 0

2 . O

2 . A

2 . O

2 . O

2 . O

1 . O

2 . O

2 . 0

2 , 4

t - O

2 . 0

2 . 0

2 . O

2 . O

2 . O

2 . O

3 3 0

2 t 4

4 9 7

2 2

t 9

2 6 8

2 6 8

) 3 2

1 2 1

I t 9 6

2 6 4

l 2 l

I 1 9 6

t 2 r

8 ' 1 , C L i n ^ ^ , C h l - ^ , F o , C " . r M o )

) L a C i n - - , F o . D i . - . r M o )

I 2 I C l i n

" . , I c , D i

s s , ( M o )

6 l ( c l i n s s , l ' o , D i s s , s p , M o )

2 4 o C l i n s s , D i s s , I o , ? S P

2 1 L C l i n - - , D i - ^ , F o , S P , a M o )

c

B

5

l 8

F

7

G

8

2 6 8 C l r ns s

l 3 O C l r n

1 9 C l i nS S

2 4 o C l i ns s

8 1 6 C l i ns s

2 6 8 C i i ns s

2 3 C l i ns s

1 2 1 C l r ns s

I C l l ns s

5 1 3 C 1 r n . . . -

3 3 0 C l i n

l / 4 C l i n

1 2 8 C l i ns s

9 6 C t i n - -

8 1 6 C l i ns s

1 2 2 C l r nS S

C l r nS S

s s

s s

S p , M e l - - , A n , c o

C 1 i n , ^ , C o , C c , ? S P

C l i n ^ - , S p , C o , ?

S D . l 4 e 1 . C o . ? C A .

C l i n . S D . C o . C c

S D . l , l e l . C A . , C A ^' s s o z

0.10.6t.?1.6

* c f . T a b l e I '

R u n s m a r k e a l I h a v e b e e n u s e d t o d e t e r m i n e u n i t c e 1 1

p a r a m e t e r s o f t h e c l i n t o n i c e m i x e d c r y s t a l s

A 1 1 a s s e m b l a g e s g i v e n c o e x i s t w i t h a h y d l o u s g a s

p h a s e , P h a s e s g i v e n i n P a r e n t h e s e s a l e c o n s i d e r e d

t o b e m e E a s t a b l e . A b b r e v i a t i o n s u s e d f o r s y n t h e s i z e d

p h a s e s : A n , a n o r t h i t e ; C A r , c a L c i u m d i a l u m i n a t e ; c A 6 ,

c a l c i u m h e x a l u m i n a t e ; C c , ' c a l c i t e : C h 1 " " , c h l o r i ! e

s o l i d s o l u t i o n ; C l i n - ^ , c l i n c o n i t e s o l i d s o l u c i o n ;

C o , c o r u n d u q ; o i . - , d i o p s i a e s o i i d s o r u r i o n i F o ,

r o r s t e r i t e : I ' t e l ' : r F l i I i L e s o l i d s o l u r i o n ; M o ,

m o n L r c e l l r L e : 5 p , s p l n e l

t92 MARTIN OLESCH

foooo l--^ i Thermol decomposit ion products o o9001 o o , r

, A - o oo o o / o \ o o

" 6o , o o 5o a a_ \_ \ o o

o

9goo i - o o r . . . . .

i I cri,,.,.xx |

-crinronites5

1.,",,.r*

| 2 { QBA5 DE 6 F 7 G I t 81,3'1,2 t \ 1,1.25,2.75,0.25

Origin of section B, section'C

Ftool-ool : .l r r v u i - o 3 |

. . . |

. - i

l . n l . . l l" l . . . . | . -J

I . .l . . i i6oof " i . . : ; J

FIc. 3" Z-X field of synthesis of clintonites on section A at pg,e = 2 kbar. A hydrous gas phase isomnipresent. Dots: single-phase clintonite; half-filled circles: cliritonite + other phases; open circles:clintonite-free assemblages. Numbers and letters just above the abscissa are the symbols of the startingmater ia ls (cf Table l ) . Proport ions given at the abscissa are the rat ios CaO:MgO:At,Or:SiO. XX and XX,stand for various phase assemblages that coexist with clintonite.

actual number of atoms are plotted against eachother (Fig. 2).

On the basis of these results, the sections A, B, andC through the system CaO-MgO-AlrOs-SiOr-HrO(c/Figs. l, 2) have been chosen in order to delineatethe field of solid solubil ity of trioctahedral 1or nearly

d1.503

1.50'l

1 .499

1.497

trioctahedral) calcium micas. The compositions in-vestigated ranged as follows (dry oxide proportionsgiven only):A. CaO:3MgO:Al,Or:2SiO, - CaO: l.25MgO:2.7 5Al,

O.:0.25SiO, (substitution Mgut + Sirv : AlvI+ Alrv)

1 2 4 C B A S D E 6 F 7 G 8

j1 8

1:3 :1 :2 1 ,2 r2 i 1 i r .2 | t2 .7 izOi .25Ftc .4 Bu lkcompos i t iononsec t ionAre la t i ve tod( inA) fo r lhe060,33 l peak .Theopenc i rc les ind ica te

multiphase assemblages; filled circles indicate single-phase mixed crystals of clintonite coexisting with ahydrous gas phase. Numbers, letters, and port ions at the abscissa as in Figure 3.

SYNTHESIS AND SOLID SOLUBILITY OF TRIOCTAHEDRAL BRITTLE MICAS I93

Tnsls 3. Results of Critical Synthesis Runs onSections B and C

at 2 kbar, with run durations up to 2897 hours. Thispressure has been selected since, for most natural

clintonite occurrences, pressures of this order of

magnitude are to be assumed (Forman, Kodama, and

Abbey, 1967a). The calculated composition of the

starting materials (water- and COz-free) and the

equivalent structural formulae of hypothetical micas

are l isted in Table l.

Section A: Trioctahedral Ca-micas,Substitution MgSi - 2Al

Starting from the Ca analog of phlogopite(CaO:3MgO:AlzOa:2SiOz:HrO), this substitutionforms less-siliceous micas with fully trioctahedral oc-

cupancy. The general formula of calcium micas in the

system investigated is Ca(Mg,Alr)(A14-"Si,Olo)(OH)r. Formicas on section A, x : | * z andy : )- z. Runs critical for the present investigation of

solid solubility are listed in Table 2. Results of 2 kbar

runs are shown graphically in the Z-X section of

Figure 3. The high-temperature breakdown products

of clintonite as well as the coexisting phases at lower

temperatures will be treated in a subsequent paper on

stabil ity relations.Despite runs of up to 115 days duration, dise-

quil ibrium assemblages have been obtained below

600'C. At higher temperatures, however, the results

are considered to represent equil ibrium phase

relations, since phase assemblages and amounts ofphases were found to be independent of run durationand because the upper stabil ity l imit of the clintonites

could be reversed (Olesch, 1972).

T-X Region of Homogeneous Clintonite

Solid Solutions

ln the central part of the T-X diagram (Fig. 3), clin-

tonite forms the only solid phase at temperatures upto 870'C. Thus, the chemical composition of these

micas corresponds to the bulk composition of the

charge (Table l). The presence of the required 2(OH)per formula unit was checked by thermal gravimetric

analysis; a single-phase product obtained from com-position 6 (Table l) yielded 4.1 wt percent water(theoretical value 4.3 wt percent). As can be seenfrom Table 2 and Figure 3, single-phase micas of thegeneral composition Ca(Mg'*,A12-,XA11-,Si,Or0)(OH), could only be grown in the range 1.4 ) z ) 0.6'The Ca analog of phlogopite (z : 2) could not beprepared.

As an additional criterion for the l imits of solid

solubil ity on this join, the X-ray properties of the

clintonites have been used. Although multiply in-

T P , . ^ D u r a E i o n C o n d e n s e d P h a s e s

r o n r t 2 ' ( H o u r s ) o b s e r v e d * * *

' " ' ( K b a r )

S e c E L O n b

9 5 8 2 ' 5 5 0

t 7 2 8 0 0

5 4 6 9 9 0

S e c t i o n c

3 3 5 9 r ' 6 5 0

l o 5 8 3 ' 5 5 0 2 . O

1 7 3 8 0 0 2 . O

5 4 5 9 9 0 5 . 0

3 5 5 7 4 ' 1 5 0 2 . O

5 9 2 t 6 5 0 2 . 0

5 1 3 ' , 1 5 0 2 . O

2 . O

2 , 0

5 . O

2 . O

5 6 9 5 5 0 2 . O

5 5 2 t 6 5 0 2 . O

5 1 6 9 6 5 5 . O

7 1 4 C l i ns s

2 8 t C l i ns s

1 2 9 5 C l i ns s

2 6 8 c l i ns s

6 9 C 1 i ns s

2 8 1 C l i n , A n , ? C o , ? S p

1 2 9 5 C l i n . C o . ?

2 6 8 C l i n . S p . ?

6 9 C l . i n . A n . S D . ?

7 1 4 C 1 l ns s

2 8 1 C I i ns s

8 0 7 c l i o . A n , C o

6 9 5 C I i n . ? A n . ? C os s _

/ | L r l ns s

6 6 C I i n . A n . S p . ?

2 8 9 7 C l i n , A n , C os s _

7 7 C I i n . A n . c o

1 3 4 3 C I r n . M a r ss s ' - s s

Z B 9 7 C l i n . A n , C os s

6 9 5 C t i n , A n . C o

1 3 4 3 C I i n . M a r q- s s

2 6 8 3 c l i n . A n , c os s

3 1 2 8 9 7

8 0 7

6 6

3 2 5 9 0 ' 6 5 0 2 . O

5 7 6 ' , 7 5 0 2 . O

3 0 5 5 3 ' 6 5 0 Z . O

5 2 4 7 0 0 2 , O

5 4 8 ' , 7 4 0 2 . O

5 1 5 9 6 5 5 . 0

2 9 5 6 7 5 5 0 2 , O

5 4 9 ' 1 4 0 2 . O

2 8 4 8 3 4 8 0

5 6 6 5 5 0

5 2 3 7 0 0

2 7 4 8 2 4 8 0

5 6 4 5 5 0

2 . O

2 . O

2 , O

2 . 0

2 , O

* c f . T a b l e l .

R u n s m a r k e d ' h a v e b e e n u s e d t o d e t e r m i n e u n i t c e 1 1p a r a m e t e r s o f t h e c l i n t o n i t e m i x e d c r y s t a l s .

* * * A 1 1 a s s e m b l . a g e s g i v e n c o e x i s t w i t h a h y d r o u s g a sp h a s e . A b b r e v i a t i o n s u s e d s e e T a b l e 2 , i n a d d i t i o n :M a r q . m a r e a r i t e s o l i d s o l u t i o n .

B. CaO:2.| ' lMgO:l .83AlzOs:1. l7SiO, - CaO:1.83MgO:l .83ALO': l .33SiO, (subst i tut ion 2 Mgv' 1A l r v : A l v r + s i r v )

C. CaO:2MgO:2Al,Oa:SiOz - CaO:MgO:2AlrO':1.5SiO, (substitution 2 Mgut + AlIv : AlvI + SiIv)

Experimental Results

Synthesis experiments on the three joins listedabove were performed at water pressures of I to 7kbar and temperatures between 300 and 1200'C. Thebulk of the data was obtained in isobaric Z-X sections

194 MARTIN OLESCH

dexed, the reflection -StC,000,3-11

well suits this pur-pose, since it shifts strongly with z, and does notinterfere with reflections of other phases present. Inaddition, the contributions of 060 and 3i1 to thispeak are independent of stacking disorder, since k :3n (Takeuchi, 1965; Takeuchi and Sadanaga, 1966).The contribution of

-3tl to this peak is very small

(Borg and Smith, 1969) and the difference in d be-tween 060 and 33t calculated from the lattice con-stants given below is, on the average, only 0.0003 Aand, within l imits of error, not systematically relatedto composition. Therefore, the position of the com-posite peak can be used with confidence. Its dvalues, plotted in Figure 4 as a function of bulk com-position, decrease with decreasing Si content in thehomogeneous samples but are, within the l imits oferror, constant in the adjoining multiphase regions ofthe T-X section. The limits of solid solubility derivedabove from phase analysis are thus reconfirmed.They are only in fair agreement with those reportedby Velde (1973) for the same join. The reasons for thediscrepancies cannot be discussed at the moment,because Velde (1973) does not give the actual datapoints.

At least at temperatures above 600oC, the l imits ofsolid solubil ity have not been found to be a functionof temperature until the upper thermal stability limitat some 870"C is attained. Similarly it could beshown that, on the MgSi-rich side of the join,pressures up to 7 kbar do not shift the l imit of solidsolubility significantly (cf Table Z). pressuredependence of solid solubil ity on the Al-rich side hasnot been checked systematically.

Solid Solubility below 600"C

At relatively low temperatures, the synthesis fieldof single-phase clintonites shrinks, mainly on the Al-rich side of the section A. For instance, at 530oC, 2kbar, the only single-phase products encountered onthis join are poorly crystall ine or disordered clin-tonites (see below) of composition z : 1.2 to z :1.15. It is at present not clear whether thisasymmetric diminution of the synthesis field of clin-tonite solid solution reflects metastabil ity or instabil i-ty of the l imiting compositions z : 0.6 and 1.4 athigher temperatures.

Sections B and C: Solid Solubilitytowards Dioctahedral Micas

As discussed above, natural trioctahedral calciummicas can exhibit l imited solid solubil ity towardsdioctahedral calcium micas. Sections B and C served

for studying these relationships, using the substitu-tion 2MgvI + AIIV : Sirv + AlvI. ln the general for-mula cited earlier, x : 4.5 - 2 z and | : z - 0.33 forsection B butx : 4 - 2 z and y : z forsection C. Sec-tion B starts from section A at z : 1.17. whereas Cstarts at z = l.0.It should be pointed out, that onlyjoin C leads directly towards margarite, whereas B isterminated at a hypothetical dioctahedral endmember Ca(Mgo.,rAlr.' 'XAlr.$Si2.1?O,oXOH)2. Criticalruns for both joins are listed in Table 3.

Single-phase clintonites on join B could only besynthesized up to z : 1.27. Variation with composi-tion of d for 060,.?31 is too small on this section to beused as a criterion for the limit of solid solubility. Itvar ies only 1.4981 A at z : l . l7 to 1,4988 at z : 1.27 .Therefore, the dependence of lattice constants oncomposition along this section was established firstfrom the homogeneous phases (see below). The limitof solid solubility was derived from the lattice con-stants b and V of clintonites in polyphaseassemblages obtained on more siliceous bulk com-positions of the section (Fig. 5, left). The effect oftemperature on the solid solubility, if any, is slight,the most siliceous mica (z = 1.27) having an oc-tahedral cation deficiency of about 3 percent.

Section C exhibits markedly higher and distinctlytemperature-dependent solid solubility of the clin-tonite phase (Table 3; Fig. 5, righQ. The limits ofsolid solubility were, again, derived from the latticeconstants. At 550'C and 2 kbar. the field of clintonitesol id solut ions extends from z: 1.0 to z : l . l7; at800"C it extends up to z : 1.24, corresponding to anincrease of the margarite component withtemperature from l7 to 24 mole percent.Solid Solubility and Properties of Synthetic Clintonites

as Compared with the Natural Mineral Phases

Solid Solubility

These experiments and X-ray data show that thefield of homogeneous clintonite mixed crystals can, atsuitable P-T-X conditions, extend to the followinglimiting compositions: Ca(Mgr.nAlo.6XAlr.65i1.40ro)(OH), to Ca(Mg,.uAl1.nXAl8.4Sio..O,oXOH), along sec-tion A; Ca(Mgr lrAlo.&XAl".$Sir.1?O1o)(OH), to Ca(Mg,.rrAlo.rrXAlr.?sSi1.rzo,o(OH), along section B;Ca(MgzAlXAlssio,.XOH), to Ca(Mg,.$Alr.2nXAl2.?6Si,,rno,'XOH), along section C. Temperature affectsonly the solid solubility towards dioctahedral micas(sections B and C). The estimated extension of thefield of synthetic clintonites is shown (Fig. 6) interms of number of silicon atoms and octahedral oc-cupancy, and compared to the natural phases. The

SNfru/ESlS AND SOLID SOLUBILITY OF TRIOCTAHEDRAL BRITTLE MICAS 1 9 5

Section B

93s1031 D

Section C

solid solubility encountered in the synthetic systemencompasses and, on the Al-rich side, considerablyexceeds the variation encountered in natural clin-tonites.

Physical Properties

The synthetic clintonites form a felt of interlockedplaty crystals of very small grain size (at most 3 pmdiameter). The scanning electron microscope showedthe subhexagonal shape of these plates. No twinninghas been observed. Only a mean refractive index (B *"y)/2 of 1.658 + 0.002 (composition z : l.O, sectionA) could be determined, which agrees with the data

r.6 1.1 1.2 r.0 0.8 0.6 0.4S i l v = Z

Frc. 6. Limit of clintonite solid solubility as a function oftemperature at 2 kbar (solid and dashed curves) in the plot (R'+ *R3+)vI us Sirv. The black dots represent compositions of naturalclintonites (cf Fig. 2).

o

a a

Ctins5

o

reported for natural clintonites. Its variation with

chemical composition is only slight.As expected, the synthetic micas are colorless.

Natural clintonites, on the other hand, show colorsfrom dark green to colorless or to brown, due toFe2+-Fe3+ and Ti3+-Tin+ charge transfer bands,respectively, according to Manning (1969).

The X-ray powder patterns could be indexed onthe basis of a lM cell (Takeuchi, 1965; Takeuchi andSadanaga, 1966). No indications of a 2M, polytype(Machatschki and Mussgnug, 1942) were en-countered. The powder data obtained agree closelywith those calculated by Borg and Smith (1969) tornatural material. There is also general agreement ofthe calculated and observed intensities of the peaks(Table 4).

On the other hand, the intensity of ftkl reflectionsdepends on bulk composition as well as on physical

conditions of synthesis. Keeping pressure, tem-perature, and run duration constant, hkl peaks

are much stronger in the Al-rich than in the Al-poormembers of the solid solution series, whereas relativeintensities of h00,0k0,001, and 201 reflections are notaffected significantly. This indicates increasing stack-ing disorder with decrease in both tetrahedral and oc-

tahedral aluminum (Smith and Yoder, 1956). As tobe expected from results of Yoder and Eugster (1955)

on synthetic muscovites, stacking disorder in the syn-thetic micas of the present study should dependstrongly on duration and temperature of the runs.Figure 7 shows the increase with time of the relativeintensity of the 7 t S reflection of a clintonite

a -\d\\o l .III

o lI

800

(Ja

o 7 0 0)ooI 600Eo

-a

I-o

I-a

aI-aI?- a

I-a

I27 28 29 3032 31 33 6

,|d.83,1.83,1.33 l'2.17d.83,1.17 I'l'2,1.5 1,2,221Frc.5. T-X diagrams for section B (left), and section C (right) at Ps"o: 2 kbar. A hydrous gas phase is

omnipresent. Dots: single-phase clintonite; open circles: clintonite + irther phases. For abbreviations see

Table2; XX stands for various phase assemblages that coexistwith clintonite. Numbers and letters just

above the abscissae are the symbols of the starting materials (cfTable l). Proportions given at the

abscissae are the ratios CaO:MgO:ALO':SiOz.

2.6

+

?28+

+NE-

3.0

3.2

o - o

o - o oII

196 MARTIN OLESCH

Ca(MgrAl)(AlsSiO,,)(OH), at two different tem-peratures. Whereas at 750'C an equilibrium valueis obviously attained after some 100 hours, theintensity of this reflection and thus also the degree ofstacking order is generally lower and increases evenafter some 600 hours at 600'C.

A selection of lattice constants of svnthetic clin-

Tnsls 4. X-Ray Powder Data of Synthetic ClintoniteCa(Mg, rAlo rXAlr rSir,OroXOH),

h k I d o b s d . " 1 " ( Q o b " - Q . . t " ) x l o 5 r / r o r " r 1 " * *

l T r s (REL . )

0.1 1 10 100 1000t (h)

Frc. 7. Relationship between the relative intensity of the i l3peak and run duration at 2 kbar,600oC and 750oC, respectively;composition Ca(MgzAlXALSiO,0)(OH)r. Low relative intensitiesof the /-/3 peak indicate stacking disorder.

tonites is compiled in Table 5. Taking into accountall determinations made on single-phase clintonites,the following regression equations have been ob-tained for the three sections.lSection A (ll data points on 9 different com-positions):

a : 0.020(4\z + 5.171(5) Ab : 0.034(4)z + 8.960(5) Ac : 0.028(6)z + 9.77OQ) AV : 4.75(53\z + 445.51(60) A8p = 100.16(2)'

Section B (6 data points on 3 different compositions):

a : -0.044(5\z + 5.2a7$) Ab : -0.031(16)z + 9.032(19\ Ac : -0.128(26)z + 9S5sQ\ Av : -8.27(88)z + 460.54(1.04) A3p : t00.r7(2)'

Section C (9 data points on 5 different compositions):

a : -0.038(6)z + 5.229(6) Ab : -0.074(t3)z + 9.068(14) Ac : -0.060(10)z + 9.857(11) Av : -9.82(7s)z + 460.0s(82) AgP : 100.16(2)"

The monoclinic angle 0 does not vary systematical-ly with composition. The other lattice constantsdecrease linearly with increasing Al content (sectionA) and admixture of a dioctahedral component (sec-tions B and C). Inclusion of a quadratic z term didnot improve the fit significantly. In general the latticeconstants obtained agree fairly well with those

I The parenthesized figures represent the estimated standarddeviation (esd) in terms of least units cited for the value to their im-mediate left; thus,5.171(5) indicates an esd of 0.005. The numberof silicons per formula unit is represented by z.

1 0

0 0 Io 2 0o 2 ll l l

- t 1 2

o 2 20 0 3t t 2

- l l 3o 2 3

1 3 0- 2 0 1- l 3 I

2 0 0r 3 l

- 2 0 2

2 0 1- t 3 2

t 3 2- 2 0 3

2 0 2- l 3 3

o 4 21 3 3

- 2 0 40 0 52 , O 3

- r 3 4

r 3 4- 2 0 5

2 0 4- r 3 5

o o 5

3 t I- J I J

t 5 2- 2 4 3

2 4 2- l 5 3- 3 r 4

0 6 0- 3 3 l

t 3 5- 2 0 5

o 6 33 3 2

- 3 3 4

9 . 6 4 4 9 . 6 4 54 . 4 9 3 4 , 4 9 84 . 0 7 9 4 , 0 7 73 . 8 2 1 3 . 8 2 03 . 5 5 6 3 . 5 5 0

3 . 2 8 9 3 , 2 8 93 . 2 t 5 3 . 2 1 53 , O 4 2 3 . O 1 1 42 . 8 2 0 2 . 8 I 82 . 6 r 5 2 . 6 1 6

2 , 5 8 6 2 . 5 8 62 . 5 8 6

2 , 5 5 6 2 . 5 5 62 . 5 5 6

2 . 4 4 2 2 . 4 4 42 . 4 4 3

2 . 3 6 9 2 . 3 6 92 . 3 6 9

2 . t 9 9 2 . 1 9 92 , 1 9 8

2 . ! O 9 2 . r 1 02 , 1 0 9

2 . O 3 8 2 . 0 3 8t . 9 2 9 0 r . 9 3 2 8

1 . 9 3 2 01 . 9 2 9 0

1 . 8 4 7 5 1 . 8 4 8 1I . 8 4 7 8

1 . 6 9 0 0 1 . 5 9 0 It . 6 8 9 4

t , 6 ) 7 6 | . 6 1 7 3r , 6 t 7 0

1 . 6 0 7 8 1 . 6 0 7 5

1 , 5 0 4 2 t . 5 0 3 2| . 6 0 2 8

| . 5 7 2 5 1 . 5 7 2 4t . 5 7 2 0

r . 5 3 9 r I . 5 3 8 6I . 5 3 8 5

t . 4 9 9 5 1 . 5 0 2 3t . 4 9 9 4I . 4 9 9 0

t . 4 8 4 3 | , 4 8 4 2t . 4 8 3 5

r . 3 5 8 9 r . 3 5 8 9r . 3 5 8 8I . 3 5 8 4

ot 2- 6

- 2 6

22

l 3- t 8

6

8- l

I- 32 8t 4

I08

- l o

l l5

6t o 7

8 3o

2 09

-23- ' t 7- 3 3- 1 6

-69

- 2 3- 2 7- 3 3

t 7 0

2 4- l I

I- 6

- 3 5

2 t 2 2J C

2 26 t 5

l l 3 2

t 4 3 97 8 4 81 3 4 0t o 2 66 t 6

1 3 1 2

1 0 0 1 0 0

2 2 1 8

t 4

l 5

2I 8

I

7

r 9

4

3

2

I

4 l

2 8

8

t 2

t 7

4 6

b

t z

2 0

5

1

o

4

4 0

6

* C o n d i t i o n s o f s y n t h e s i s : 8 6 5 " C , 2 K t a r , I 2 Jh o u r s ,

X - r a y d i f f r a c t o g r a n w i t h i n t e r n a l S i s t a n d a r d .

* * I ( P K ) B o r g a n d s n i t h ( I 9 6 9 , p . 6 I 3 )

SYNTHESIS AND SOLID SOLUBILITY OF TRIOCTAHEDRAL BRITTLE MICAS

TlsI-B 5. Selection of Unit Cell Parameters of Single Phase, Mixed Crystalsof Clintonite from Sections A, B, and C

. (E ) b ( 8 )"

( 8 ) A ( o ) v ( 4 " )

S e c t i o n A

c

6F7

S e c t i o n B

l o

S e c t i o n c

3 33 l3 23 0

9 . 8 0 6 r ( 2 3 )9 . 8 0 1 0 ( 3 3 )9 . 8 0 7 7 ( 2 9 )9 . 8 1 0 1 ( 2 8 )a ? q R ? / ? 7 \

9 . 7 9 5 6 ( 4 1 )

9 . 7 9 3 6 ( 2 7 )

9 . 8 0 0 s ( r 7 )9 . 7 9 8 2 ( 3 2 )

9 , 7 9 5 7 ( 1 9 )9 . 7 9 0 1 ( r 9 )9 . 1 8 7 9 ( 2 2 )9 . 7 8 t 8 ( 2 2 )

l 0 o . r 8 ( 2 )1 0 0 , l 5 ( 2 )t o o , l 3 ( 2 )r o 0 . l 8 ( 2 )i 0 o . r 5 ( 2 )r 0 0 . 1 3 ( 3 )l o o , l 8 ( 2 )r o 0 . l 8 ( r )

r o 0 . l 7 ( 1 )1 0 0 . r 8 ( 2 )

r 0 0 . 1 6 ( r )l o o , l 8 ( r )1 o 0 . 1 7 ( 2 )r 0 o , r 7 ( 2 )

4 s 2 . 0 8 4 ( r 3 3 )4 5 1 . 3 5 6 ( 2 3 7 )4 5 ! . 5 6 0 ( 1 9 6 )4 5 r . 8 8 8 ( r 6 7 )4 5 o , 5 3 8 ( l 7 l )4 5 0 . 3 3 2 ( 2 7 O )4 4 9 . 7 6 8 ( l 6 r )4 4 9 . 1 9 1 ( r 3 0 )

4 5 0 . 6 8 4 ( l o 3 )4 5 0 . 2 5 l ( l 8 7 )

4 4 9 . 7 2 t ( t t 3 )4 4 9 , 2 9 7 ( t 2 2 )4 4 8 . 6 9 2 ( r 3 8 )4 4 8 . 0 8 4 ( 1 4 5 )

1 6 9r 6 83 8 9t 0 03 3 9

4 53 2 4i 7 0

5 5 5

5 7 55 4 75 9 05 4 5

5 . 2 O 0 2 ( 9 ) * * * 9 . 0 0 7 5 ( 1 6 )5 . l 9 s 5 ( 1 8 ) 9 . 0 0 4 s ( 3 2 )5 . r 9 4 2 ( l s ) 9 . 0 0 4 4 ( 2 3 )5 . | 9 8 4 ( r 3 ) 9 . o o 2 7 ( 2 1 )s . r 9 2 4 ( 1 3 ) 8 . 9 9 6 4 ( 2 1 )s . 1 9 0 8 ( r 9 ) 8 . 9 9 7 o ( 3 2 )s . r 8 8 4 ( 1 3 ) 8 . 9 9 2 4 ( 2 2 )5 . r 8 7 8 ( 9 ) 8 . 9 e 5 2 ( r 5 )

5 . r 9 3 s ( 9 ) 8 . 9 9 s 9 ( 1 4 )s . r 9 2 0 ( r 4 ) 8 . 9 9 2 t ( 2 3 )

5 . r 8 9 4 ( 9 ) 8 . 9 8 7 9 ( t 5 )5 . l 8 9 o ( 8 ) 8 . 9 8 5 i ( 1 6 )s . l 8 4 s ( l l ) 8 . 9 8 3 3 ( t 6 )s . r 8 4 3 ( r o ) 8 . 9 7 5 8 ( r 9 )

* s e e T a b l e L

* * s e e T a b l e 2 a n d T a b l e

* * * P a r e n t h e s i z e d f i g u r e sI e a 6 t u n i t s c i t e d f o ra n e s d o f O . O O 0 9 ,

3 .

r e p r e s e n t t h e e s E i E a t e d s t a n d a r d d e v i a t i o n ( e s d ) i n t e r m s o f

t h e v a l u e t o t h e i ! i a n e d i a t e 1 e f t , t h u e 5 . 2 0 0 2 ( 9 ) i n d i c a t e s

reported for natural clintonites (Table 6), the latterbeing, however, slightly, but systematically, higher:

synthetic clintonites

s. lS - 5 .20 A8.97 - 9.01 A9.78 - 9 .81 A

Probably this difference stems from the presence ofadditional large cations (Fe2+, Fe3+, Na, Ba) in thenatural phases. The systematically higher densitiesof natural clintonites, ranging from 3.035 (Kokscha-row, 1875) to 3.081 g cm-' (Eakle, 1916), as com-pared to densities calculated from unit cell data for

Tlrlr 6. Unit Cell Parameters of Natural lMClintonites, Taken from the Literature

" ( R ) b ( 8 )

" ( R ) R C ) A u t h o r s ; I o c a r i o n s

the synthetic micas-2.936 to 2.969 g cm-3-may besimilarly explained.

Crystal Chemical Properties

The most interesting crystal chemical features ofboth synthetic and natural clintonites are (l) com-plete or nparly complete occupancy of the interlayerposition by Ca; (2) rather limited solid solubilitytowards dioctahedral micas; and (3) a ratio of Si/AIIVof less than one.

The small Ca cation in the interlayer causes a dis-tinct contraction of the mica structure in the c direc-tion, compared to the alkali micas (Hazen andWones, 1972), as well as a diminution of the D dimen-sion (Radoslovich, 1962). Natural clintonites exhibitan octahedral occupancy between 3.04 and 2.8'7,which is a slightly smaller variation than encounteredin the synthetic system (3.0 - 2.76). Ordering amongoctahedral Mg,Al and (possibly) vacancies in theclintonites is not very well understood at present. Inmost micas the smaller trivalent cations are concen-trated in the two topologically equivalent octahedralsites, the divalent cation preferring the third, struc-turally distinct site (Veitch and Radoslovich, 1963).These relationships are, according to Takeuchi (1965)and Takeuchi and Sadanaga (1966), just reversed inthe trioctahedral calcium micas. This might explainthe rather limited solid solubility towards dioc-tahedral micas.

The trioctahedral calcium micas show extremelv

natural clintonites

a 5 . r9 - 5 .25 Ab 9.00 - 9.03 Ac 9.80 - 9.97 A

5 . 2 0 4 9 , O 2 5 9 , 8 1 2

5 , 2 t 5 9 , O t 2 9 . 8 5 4

5 . 2 5 9 . 0 0 9 . 8 1

5 . 2 1 5 9 . 0 1 3 9 . 8 5 3

5 . 2 1 9 . 0 2 9 . 9 7

5 . 1 9 9 . 0 0 9 . 8 0

5 , t 9 4 9 . 0 0 3 9 . 8 0 2

1 O 0 . 3 3 F o r n a n e t a 1 ( 1 9 6 7 a ) ;S h i s h i n s k a j a G o r a , S l - a t o u 6 t

1 0 0 , 0 8 i b i d . ; N i k o l a j e l l a x i m i l i a -n o w s k , A c h n a t o w s k , U r a l

1 0 0 . l 7 t , o r E a n * ( 1 9 5 1 ) ; i b i d ,

1 0 0 . 0 7 i b i d . ; C r e s t n o - e , C a 1 i f .

1 0 O . 0 5 S a n e ! o ( 1 9 4 0 ) ; L a g o d e 1 l aV a c c e , A d a n e l l o , A l p s

1 0 0 . l 3 S t e v e n s o n a n d B e c k ( 1 9 6 5 ) ;T o b e c c o R o o t M o u n t a i n s , M o n t ,

l O O . l O T a k e u c h i ( 1 9 5 5 ) ; C h i c h i b uM i n e , J a p a n

* V a 1 u e 6 g i v e n b y F o r m a n ( 1 9 5 1 ) i n K X u n i t s h a v e b e e nr e c a l c u l a t e d i n t o I u n i t s .

MARTIN OLESCH

A l r v a . ( R ) " r { R ) * *

t 1 . o s 1 1 1 ' q 6 2 1 1 1 . . . r ,

Tlglr 7. Calculated Tetrahedral Layer Rotation ain the End Members of the Sections Investisated

calcium micas performed at Kiel University and accepted as a

thesis by Ruhr-University Bochum. I thank F. Seifert for helpful

discussions during the course of the study. Provision of laboratoryfacilities at Mineralogisches Institut, Kiel University, by the late F.

Karl and at the Institut fiir Mineralogie, Ruhr-University Bochum,by W. Schreyer are gratefully acknowledged. The paper has hadthe benefit of review by P. K. Hdrmann, Kiel; K. Langer, Bochum;and F. Sei fer t , Kie l .

References

ArsuNoov, Y. A., K. S. Mruroov, AND N. V. Belov (1961)Crystal structure of brandisite. Dokl. Akad. Naak. SSSR, 137,167-170 (in Russian).

BrrNcHr, A., eNo O. Hrere (1946) La xantofillite dell'Adamellomeridionale. Period. Mineral. 15, 87-146.

Borc, J. Y., nNo D. K. Stunu (1969) Calculated X-ray powderpatterns for silicate minerals Geol. Soc. Am. Mem. 122,896 p.

BunNHru, C W. (1962) Lattice constant refinement. Carnegie Inst.Wash Year Book, 61, 132-135.

Csnrsropnr-MIcHEL-LEvy, M. (1964) Synthdses hydrothermalesdans le systdme gehl6nite-akermanite, Ca,ALSiOr-CazMgSi,O"en milieu carbonat€. Bull. Soc. franc. Minbral. Cristallogr. 87,28-30.

Cunxr, F. W., AND E. A. ScsNsrorn (1892) Experiments uponthe constitution of certain micas and chlorites. Am. J. Sci. 143.378-386.

Cnowrrv, M. S., eNo R. Roy (1964) Crystalline solubility in themuscovite and phlogopite groups. Am. Mineral. 49, 348-362.

Dorrrnn, C. (1917) Handbuch der Mineralchemie. Bd. Il, 2.Abteilung, Verl. Th. Steinkopff, Dresden und Leipzig. ll44 pp.

Eerun, A. S. (1916) Xanthophyllite in crystalline limestone. ,/.Wash. Acad Sci. 6. 332-335.

Flnurn. V. C.. ltto B. Vnlor (1973) Effects of structural orderand disorder on the infrared spectra of brittle micas. Mineral.Mag. 39,282-288.

FonurN, S. A. (1951) Xanthophyl l i te. Am. Mineral.36,450-457.-, H. KoDAMA, AND S. ABBEv (196'la) A re-examination of

xanthophyllite (clintonite) from the type locality. Can. Mineral.9. 25-30.

, AND J. A. Mnxwrl l (1967b) The tr ioctahedralbrittle micas. Am. Mineral. 52. 1122-1128-

FneNcH, B. M., AND H. P. Eucsrrn (1965) Experimental controlof oxygen fugacities by graphite-gas equilibriums. Geophys. Res.10.1s29-1539.

GEBERT, W. (1972) Die Kristallstruktur von Ba,rAlrrSi,oO... Z.Kristallogr. 35, 437 -452.

HrurlroN, D. L., ANn C. M. B. HeNornsoN (1968) The prepara-tion of silicate compositions by a gelling method. Mineral. Mag.36, 832-838.

Heneoe, K., H. Kooeue, AND T. Suoo (1965) New mineralogicaldata for xanthophyllite from Japan. Can. Mineral. 8, 255-262.

H,qzrN, R. M., ltto D. R. WoNBs (1972'lThe effect of cation sub-stitution on the physical properties of trioctahedral micas. Am.Mineral. 57, 103-129.

HINrzE, C. (1897) Handbuch der Mineralogie. Bd. 2, Silikate undTitanate. Verl von Veit, Leipzig. l84l p.

HussNrn, J. S. (1971) Buffering techniques for hydrostatic systemsat elevated pressures. In, J. C. Ulmer, Ed., Research Techniques

for High Pressure and High Temperatures, Springer Verlag, NewYork.

Iro, J., ,tNo J. E. AnBu (1970) Idocrase; synthesis, phase relationsand crystal chemistry. Am. Mineral. 55, 880-912.

c ( ( c a I c ) a c c o r d i n g t o

R a d o s l o v i c h H a z e n a n d

a n d N o r r r s F t o n e s ( t y l 2 ,

( t e 6 2 )

( t o . z o ) ( l o . a o )

B

c

2 , 6 1 . 7 1 8 9 . 0 0 83 . 4 1 . 7 4 8 8 . 9 8 1

2 , 8 3 t . 7 2 6 8 . 9 9 62 , 7 3 t , 7 2 3 8 . 9 9 3

3 . 0 t . 1 3 2 8 , 9 9 42 . 1 6 1 , 1 2 4 8 . 9 7 7

2 2 . 12 5 . I

2 2 , 9

2 3 , O

2 2 , O2 4 . 1

2 2 . 42 2 . 7

2 3 . 42 2 . 1

T h e a v e r a g e t e t r a h e d t a l b o n d l e n g t h d _ h a s b e e no b t a i n e d b y l i n e a r i n t e r p o l a t i o n o f

' t h e d a t a

b y S m i t h a n d B a i l e y ( 1 9 6 3 ) g i v e n f o r l a y e r s i t i c a r e s .

b o f c l i n r o n i t e s s y n t h e s i z e d i o t h e p r e s e n t s t u d yh a s b e e n ! a k e n f r o m t h e r e g r e s s i o n e q u a t i o n s ( c f .t e x r ) .

low Si /Al Iv rat ios, f rom 1.4:2.6 down to 0.6: 3.4. Thelarge amount of Al distributed randomly oyer thetetrahedral sites (Takeuchi and Sadanaga, 1966;Farmer and Velde, 1973) increases the size of thetetrahedra compared to other, more sil iceous, layerlattice silicates. To account for the different unit sizeof octahedral and tetrahedral layers, the tetrahedrahave to rotate around their trigonal axis, which isperpendicular to (001). The angle of this rotation canbe calculated either from the relation d : arc cos(b"b"/(9.051 + 0.254 X-) where X : number ofAl atoms per 4 tetrahedral sites (Radoslovichand Norrish, 1962), or from d : arc cos (bob'/4 - {-2 . dr) where d1 : average tetrahedral bondlength (Hazen and Wones, 1972). Such calculationsfor a (Table 7) agree with the value reported byTakeuchi (1965) for clintonite (23'). They show thata increases with a decrease of the Si/Alrv ratio. Theserotations are the largest calculated so far for layer lat-t ice sil icates. On the other hand a decreases on in-troduction of a dioctahedral component into themica structure, approaching the value for margarite(21 ' ; Takeuchi , 1965).

The presence of 65 to 85 percent Al on thetetrahedral sites necessitates the existence of an un-usually large number of tetrahedral Al-O-Al bonds,which is at variance with Loewensteins' statement(1954) that such bonds are energetically unfavor-able and should not occur. Similar violations ofLoewensteins' rule have recently been reported byMoore (1969), Gebert (1972), and Lin and Burley(1973 ) .

Acknowledgments

The present paper forms part of a general study oftrioctahedral

.STN?H''S1S AND SOLID SOLUBILITY OF TRIOCTAHEDRAL BRITTLE MICAS t99

Kocs. G. (1935) Chemische und physikal isch-optische Zu-sammenhlinge innerhalb der Sprddglimmergruppe. Chemie derErde,9, 453463.

Korscuenow, N. (1875) Material ien zur Mineralogie Russlands.Zweiter Anhang zum Xanthophyllit. Watuewir. Vol. VII,346-374, St. Petersburg.

Llnexnnr, A. (1921) Uber die Petrographie und Mineralogie derKalksteinlagerstatten von Parainen (Pargas). Bull. Comm. Geol.Finlande, 54, I 13 pp.

LrN, S. B., AND B. J. Bunrny (1973) The crystal structure ofmeionite. A cta C rystallogr. B.29, 2024-2026.

Lorwrnsrrru, W. (1954) The distribution of aluminum in thetetrahedra of silicates and aluminates. Am. Mineral 39,92-96.

Luru, W. C., eNo O. F. Turrlr (1963) Externally heated cold-sealpressure vessels for use to 10,000 bars and j50"C. Am. Mineral.4t. l40l-1403.

MrcunrscHrr, F., AND F. Musscrluc (1942) Uber dieKristallstruktur des Chloritoids . Naturwissenschaften, 30, 106.

MeuNINc, P. G. (1969) On the origin of colour and pleochroism ofastrophyllite and brown clintonite. Can. Mineral. 9, 663-677.

Moonr, P. B. (1969) The crystal structure of sapphirine. ,42Mineral. 54,3149.

NIror-nrtw, P. D. (1883) Chemische Zusammensetzung desWalujewits (abstr.). Z. Kristallogr. 7, 634-635.

- (1884) Zusammensetzung des Xanthophyllits (abstr ). Z.Kristallogr. 9, 579-580.

Orescu, M. (1972) Synthese und obere Stabilirat vontrioktaedrischen Calciumglimmern (Clintonit, Xanthophyllit)(abstr.). Fortschr. Mineral. 50, Beiheft l, 7S-77.

(1973) Synthese und Stabilitiit trioktaedrischerCalciumglimmer (Clintonit, Xanthophyllit, Brandisit). Thesis,Ruhr-Universitiit Bochum.

Pnrrns, T. (1970) A simple device to avoid orientation effects in x-ray. Norelco Rep. 17,23-24.

RnoosLovrcH, E. W. (1962) The cel l dimensions and symmetry oflayer-lattice silicates. II. Regression relations. Am. Mineral. 41 ,6t ' t-636.

-, AND K. Nonnrss (1962) The cel l dimensions and symmetryof layer-lattice silicates. I. Some structural consideratrons. arn.Mineral. 47. 599-616.

Roy, R., AND O. F. TurrLr ( l96l ) Investigations under hydrother-mal condi t ions. In, L. H. Ahrens, K. Rankama, andS. K. Runcorn, Eds., Physics and Chemistry of the Earth,Vol . l . Pergamon Press, Oxford. p. 138-180.

Sereno, E. (1940) La struttura della xantofillite. Period Mineral.l t , 53-77.

Sntrnnr, F. (1970) Das pefiogenelische Ps"s-T-Netz des SystemsM gO-A l,O

"-S|O2-H "O im D ruck-Tempi-ratur-B e reich 0-7 K b,

400-1250"C. Habilitationsschrift, Ruhr-Universitiit Bochum,154 pp .

Sutrn, J. V , eNo S. W. Berlry (1963) Second review of Al-O andSi-O tetrahedral distances. Acta Crystallogr. 16, 801-811.

- , AND H. S. YoDER, Jn. (1956) Exper imental and theoret icalstudies of the mica polymorphs. Mineral. Mag. 31, 209-235.

SrsvsNs, R. E. (1947) A system for calculating analyses of micasand related minerals to end members. U.S Geol. Suru. Bull.950,l 0 l - l 1 9 .

SrrvrNsoN, R. G., ervo C. W. Brcx (1965) Xanthophyl l i te f romthe Tobacco Root Mountains, Montana. Am Mineral. 50,292-293.

TrrrucHr, Y ( 1965) Structures of brittle micas Clays ClayMinerals, Proc. l3th Nat. Conf. 1964, 1-25.

-, AND R. SenaNlc,t (1959) The crystal structure ofxanthophyllite. Acta C rystallogr. 12, 945-946.

- , AND - (1966) Structural s tudies of br i t t le micas. 0)The structure of xanthophyllite refined. Mineral. J. 4, 424-43'l .

TscHrnunx, G., nNo L. Srpcicz (1879) Die Cl intoni tgruppe. Z.Kristallogr. 3, 496-515.

Vnrrcn, L. G., euo E. W. RADosLovrcH (1963) The cel l d imen-sions and symmetry of layer-lattice silicates. III. Octahedralordering. Am. Mineral. 48, 62-75.

Vslor , B. (1973) D6terminat ion exp6r imentale de la l imi te destabilit6 thermique sup6rieure des clintonites magn6siennes(abstr.). Reunion Annu Sci Terre, Paris, ln3. 409.

Yoosn, H S. , Jn. , nNo H. P. Eucsrrn (1955) Synthet ic andnatural muscovites. Geochim. Cosmochim Acta, B. 225_290.

Manuscript receiued, June 4, 1974: accepted

for publication, October 31,1974