American Mineralogist, Volume 60, pages l04l-1O46,
1975
Cookeitewith a Perfect RegularStructure,
Formedby Bauxite Alteration
Zove Y. VnugLsvsrnJe,Icon S. DrlrrsrN, BoRrsB. Zvye,clN,
nNn SvEu-nNnV. Sosolnvn
Institute of Geologyof Ore Deposits,Petrography,Mineralogy, and Geochemistry
Academyof Scienceof the U.S.S.R.,Moscow, U..S.,S.R.
Abstract
A di,trioctahedralLi-chtoritecookeite(Lio.?Alr.r
.,
,rISi,,rAlou2],.oO,o
)r.s(Alr.r"Fe;.tnFe3.+or),
(OH)t"u,with an exceptionally
perfectcrystalstructurehasbeenfound in bauxiteof Djalair
(Middle Asia). High-voltagediffraction(oblique-texture)
patternswereusedfor its structural
..identification.It was establishedthat it is a oneJayertriclinic polytypelo'uo'rlraraloLoll
w i t h s y m m e t r y Cai n d u n i t c e a
l l : 5 . 1 4 , b : 8 . 9 0 , c : l 4 . l 5 A , a : 9 0 o 3 3 ' , A : 9 6 " 1 2 ' , 1=
90'. The smalldeviationofa from 90oresultsin very peculiarfeaturesofthe diffractionpatterns,giving the falseimpressionof a monocliniclattice but with two non-selfconsistent
Bvalues.
The formation of the cookeiteinvestigated
is the final resultof a peculiartransformationof
bauxite rock following an intermediatestage of formation of a two-layer monoclinic
pyrophyllitepolytype.
Introduction
Unlike trioctahedral chlorites, dioctahedral and
di,trioctahedralvarietiesare much lessabundant and
are therefore of great interest in the crystal chemistry
and genesisof minerals. In this respectthe di,trioctahedral Li-chlorite cookeite, found in bauxites of
Djalair (Middle Asia), is especiallyremarkable.This
chlorite, belonging to the concluding stage of a
peculiar transformation process in bauxite rock,
proved to be unique in its high degreeof structural
order, which permitted its polytype identification.
Environmental Conditions
The bauxite of the Djalair deposit is interbedded
betweenthe Upper and Lower Carboniferous in the
zonesof the terrestrialbreak. Limestones,underlying
bauxite, underwent some karst development. The
resultant small cavitieswere later filled with bauxite
matter. In areas of intense karstification sheet-like
bodiesof bauxiteoccur, but thesecompletelythin out
as undissolved limestone is approached. Subsequently, the bauxite serieswas overlain by younger
middle Carboniferous limestone.
Later the whole rock serieswas metamorphosed.
As a result limestonewas marmorized while bauxite
was partly convertedto emery.At presentthe bauxite
bed forms a number of disconnectedareas with a
thickness of up to 3 m. In one such area, near its
lower contact (in a zone up to 0.4 m thick), the bauxite bed is broken into blocks up to 0.1 m in size.The
joints between the blocks are filled with pyrophyllite.
In some casesthe developmentof pyrophyllite is so
intensivethat blocks of bauxite, partly transformed
into emery, appear to be enclosed in cells of a
pyrophyllite net.
Specimensof brown bauxite with compact shot
texture from this area, kindly provided by A. P.
Gapeev, contain scaly aggregates of greenish
pyrophyllite. The pyrophyllite flakes, up to 4 mm in
length, are usually arranged normal to the selvage
joints. According to electron diffraction oblique texture patterns, the pyrophyllite belongs to the
widespread 2M - mo dification o sosr p s6sr56sos (Zv y agin, Mischenko and Soboleva, 1968). Distinct,
weak, glide surfaces or zones developed in the
pyrophyllite, commonly along an oblique direction
relative to the long axes of the scaly pyrophyllite aggregates. The material filling these zones strongly
differs from the pyrophyllite both in color (white or
bluish gray) and texture (from fine-grained to macrocryptocrystalline). Exceptionally good electron
diffraction texture patterns with a great number of
very clear, sharp, and well resolvedreflectionshave
been obtained for this material. The analysis of the
reflection set has indicated that the specimen is a
di,trioctahedral chlorite with a regular structure indicative of a definite polytype.
r042
VRUBLEVSKAJA, DELITSIN, ZVYAGIN, AND SOBOLEVA
Chlorite Polytypes
unit cell, spacegroup symmetry,and components
Sincechlorite structuresconsistof two kinds of (xn,!n) of the c axis in normal projectionon the ab
alternatinglayers,which may have differentrelative planeare indicated.
displacements
and orientations,
an enormousvariety
Electron Diffraction Featuresof
of polytypesis possible.All thesepolytypescan be
Chlorite Polytypes
dividedinto six groupsdifferingby the projectionon
In the courseof electrondiffractionstudyof,layer
the planeac of the chloritepacket (:repeating comsamplesof dioctahedral
anddi,trioctahedral
bination of layers).Thesegroupshavebeen desig- silicates,
nated by Bailey and Brown (1962) as Ia-2n, lb-2n, chlorites from different depositsof the USSR and
other countrieshavebeenidentifiedand examined.
IIb-(2n1 l),Ila-2n,lla-(2n * l),llb-2n, whereI {
2n,2n + I < 4. Zvyagin(1967)has usedfor these Accordingto the intensitiesof the k : 3n reflections,
groupsdesignations
o, o',lol,lo'l,lo,lo', hereo being most of thesechloritesconsistof packetslo'1, the
a generalsymbol for intersheetdisplacements
in an othersconsistingofpackets o. The k I 3n reflections
2:l layer.A prime or its absence
indicatesthe relative that indicate 3-dimensionalstructural regularity,
orientationof octahedralsheetsof both layersof the though sometimespresenton the patterns,were inpacket:in packeto' they havethe sameorientation sufficientfor unequivocalidentificationof polytypes.
and in packeto, oppositeorientations.The vertical In contrastthe chlorite from the bauxiteof Djalair
lineindicatesa superposition
of octahedral
cationsof has a much more regular structure,and its oblique
the hydroxidelayer and of the adjacenttetrahedral texture patterns(Fig. l) offereda favorableopporcations in the normal projection on the ab plane. tunity for a preciseanalysisof the lattice geometry
Within eachof the sixgroups,thepolytypestructures and a reliablepolytype identification.
differ by intersheetand interlayerdisplacements
of
Lattice Geometryof the Cookeite
Xb/3 along the b axis.
If thesedisplacements
are randomlydistributed, The geometryof texturepatternsmight appearat
Bailey and Brown (1962) call the corresponding first glanceto satisfythe "rnonoclinic" arrangement
polytypes"semirandom."For any of the polytype of rtflections.In a monocliniccasethe heightsDgroupsthere is one semirandompolytypewith the namely,the distancesof reflectionsfrom the minor
same designation.Natural chlorites are usually axisofthe ellipses,
thesedistances
beingproportional
semirandom,the o-polytypebeingmore abundant. to the projectionsofreciprocallatticevectorslhkllon
Semirandompolytypeswith packet o',o'l,lo'l are the c* axis-depend only on indicesh,l becauseD :
morerare,whilethosewith packetslol ,ol havenever hp + lq wherep - c*cos0*, q - c*. The reflections
beenfound.
021,lll are disposednon-uniformlyalongthe first elRegular polytypes have quite definite intersheet lipsein the patternsof the chloritestudied,while the
displacements
differingby componentsalong axesa,b 201,201,l3l, l3l reflections
of the secondellipseare
of their normalprojectionon planea6, specified
by groupedin compactsetsof four reflections(Zvyagin
s u b s c r i pit s= 1 , 2 . . . 6 a n d * , - , 0 ( Z v y a g i n , 1 9 6 7 ) et
. al, 1972).Such peculiaritiesusually mean that p
In additionto displacements
o insidethe 2:l layer, differsfrom q/3-thatis, p/q differsfrom l/3-to the
the displacement
z betweenadjacentsheetsbelonging extentthat 0 deviatesfrom its idealvalue.The realD
to different layers must be specified.For a trioc- valueshave indicated,however,that the ratiosp/q,
tahedralhydroxidelayer,r is measuredbetweenthe determinedseparatelyfrom the first and secondelorigins of the tetrahedralsheetsadjoining the in- lipse, are non-equal,the first (0.305)being smaller
termediatehydroxide layer. Any chlorite structure and the second(0.375)beinggreaterthan l/3. These
may be thus describedby a succession
of letterso, r two plq ratios lead to two differentp valueshaving
with conventionalmarks and subscripts.
oppositedeviationsfrom the idealB value,for which
Regularpolytypesare ratherrare.Usuallythey ap- p/q : l/1 and c'cos?/a : -l/3. To resolvethis
pear in single crystals and are more probable for paradox,the heightsD for the secondellipsereflecdioctahedraland di,trioctahedralchlorites because tions werecalculatedby useofp and q valuesdetertrioctahedralvarietiesare lesssensitiveto displace- mined from the heightsD of the first ellipsereflecments(tbl3) alongtheb axis.TableI listsall regular tions, and then compared with the experimental
polytypesknown to dateincludingthe cookeiteunder values.As it turned out, the inner and the outer
study. For each polytype the symbolic notation, reflectionsof the abovementionedsetsof four reflecmodeof octahedralpopulation,numberof layersper tions essentiallydiffer by degreeof agreementof
1043
COOKEITE FORMED BY BAUXITE ALTERATION
TesI-r l.
lfurber
otr
latoa].
Experimentally
IdentifiedRegularChloritePolytypes
Synboll.o
scocrdiJlg to
o 1il5:t"/ il'fi zw"eoroezraotatlon3*'iI;.HIB#3$'l.,r.rr
i,-rrt-z
-1/3.o
(rrb-z)
B
S
T
I
I
Z
B
S
-1/3'O
(1/3,o)
donbassl.te
D-l[
-t/3ro
('t/3.o)
ch].orlte
C
T
B
Or-1/3 ohlorl.te
D
T
B
alonbasslte
D
DA
Cr-culorlte
T
BB
2',l
c7
6zr+62
( o61266)
ia-I.I'b-G
(rrb-4))
(q-rrb-+
C2/c
631163r.563
( 65.i4651266)
x1-Ib-3:1-Ib-5
{ia-rru-6:ir-lrt-+)
c4
63a565r5o3
(66;12621266)
x1-1b-5:r2-Ib-5
(i1-rrb-4:*2-rrb-4)
c7
63a361T
5o1rj63
( o5f5 o4r2 041666)
ti.-rru-e:*r-rru-+i;r-rruz)
(o,1/3)
qo[lt_.r. lo-il)
xa-Ila-1
(1..-!e-2 (Ia-2))
0/3,o)
16;lr_16;l
q6.ilt+l6,il)
(ra-a)
i'r-ta-t
(xr-Ila-1 )
1/3,-1/3
(-1/3.0)
xz-Ila-1
(i.-ra-5
-l/3,O
g/3r1/3)
ci
F?l r*r_ l6il
16llr r
16l-l
i.Zi)
d4i=l"l
c2/c lo;lt_ lo;l lu;l
".
cc
cc
10
-l/3,o
(-1/3,-1/3)
-lbrA
(ra-6))
-'t/3ro
ir-ra-+:ia-ta-6
x?-IIa-5:x2-IIa-3
loilr loglt.loil
(il-ra-e:irlre-2 I
ftelr. lo4lr- loil)
x"-If,a-1:xr-IIa-1
bil r+16;lr-l6il
q6el'r_
I6ilr. loet) (ii-ta-+,*.r2u-a1
r+'r-+
l6blr_-r-l6hl i"- ra-2:ir-ra-2
164l
q6;lr.t l6ilr-r_l6el)fii-ra-+:i]-ra-+ I
ia-ta-G:ir-te-6
r+ l6ilr_ 166l
l6GI
(;z-IB-2:i3-Ia-2 )
{o21.r.
lo4lr_ loip
.c3661
d;l 12651
(6;l11qtr26iD
B
BB
DA
DI
IrB
.
.
.
-
Br1t1t[Ley et el' 1tJ0
Brorlr Balleyr 4963
Drltsr Al,exeadrovar 196?
hlts'
Ira6a^renko, 195?
Ilster,
B&1leyr 195?
D-T
cookeLte
1/ 3 , 0
?'t /3,1/3)
verhl.ou].lte
MW
I /3,o
( - 1/ 3 , 1 / 3 )
vernl.cu]-lte,,r"T
oookelte
0 r o Cr-ohlor1te
(o'o)
.
.
-
Tbl.s
TA
MW
-1 /3,-1 /3
F1/3,o'
ilW
S
SB
Ihl-s
Z
W
D-T
oookelte 2
Te!o1ou11te,,J, I
- 1 / 3 , O donbaesltD
(-1 /3i /3)
i,'-La-3:xr-IIa-6
(xr-IIa-2:-xr-Ta-'l)
H*,:1"- **;
T
I
CZln
x4-fb-1:xa-Ib-5rx"-Ib-1
sa'lle ne'e
pennl.ne B
trnoobJ.orlte
ohl.orlte
pennlD€ A
ch.Lori.te
11
Cz
61116.o
L,Yn
,,9" T
Mw
D
Dtr
f
16
1
l,lathl.esoD, lilalker,
1954
Stelnflnkr
1958
Shlrozu, Ba11ey, 1956
thl.s uoxk
ZtysgLnt 1953
'To
s1opllfy
the deElgnetl-oDs of oeatroEy@etrlc
2:1 layer sLng3.e oynbols 6i insteBd of double
eynbolo
6;di are ueeil. In lnrentheoee
axe gl.ven whl.ch corIespond elther
altemetLve
notatlona
to an orlentetloa
i,,, of the fbst
layer or to a ceIl il1th ody one obll.que engle o( or P (yo
ora-o).
'*Botb
structuree
are corneoted by a reflexJ.o! ln a plaDe nornel to the b -axls or W 18oorotatlon
aroutil tb€ 6 -ai.6.
***AU
(oonpoeltloa illfferenoee
theEe four etruotUres
bel,ng negleoted) are 1t1 feot ooDgruent.
Aft€r rotatlon
rltb
by 18Oe arourd, c*the struotures
eyeD subeorlptg
ld'l booaD€ equlvilt4t
rotatloD by 1gO'
to yerEl'ou].1.te,,i'i rbl-cb la 1ts tur! traaefera
1ato, yerol.ouflte,,g"after
-axls
,
arouDil the
c/2.
ooobj.ned witb a tralllatLon
1044
VRUBLEVSKAJA, DELITSIN, ZVYAGIN. AND SOBOLEVA
FIG. I Electron diffraction oblique texture pattern of the Djalair
cookeite (inclination angle @ : 70').
calculated and measured D values. Taking into account that the reflections of the second ellipse have
the hk indices20,r0,13, or I3, one can concludethat
such a discrepancy is due to a small "triclinic" distortion of the lattice (a I 90"). As a consequencenot
only p I 0 butalso s - b*.cos a* I O,so that in fact
D : hp f ks * /4. This distortion does not affect the
positions of the k : 0 reflectionsbut its influenceon
the positions of the k + 0 reflections becomesmore
pronounced as k increases.The splittingof the k + 0
reflections must lead in principle to an increaseof the
number of reflectionsin an interval AD : q, but if s is
small, this may not be revealed.lf I Fhhtl 11 | Fni,l , the
inequality s I 0 is manifested only by small displacements of reflections against their theoretical
"monoclinic" positions.For this reasonthe heightsD
of the first ellipsereflections(k : 1,2) lead to rough
but yet reliable-at least concerning the relation
p/q-values p,q. The values of p,q so obtained indicatep/q < l/3. Therefore in the "monoclinic" sets
of four reflections on the second ellipse, the outer
reflectionsmust have indices 1.3l,13.l+1, while the
i n n e r o n e sh a v e i n d i c e s2 . 0 . t + 1 , 2 0 1. l f s I 0 , e a c h
-t3/
reflection 131,131,13/.
splits into rwo reflections
with opposite signs of k, one moving away from and
the other toward a20l reflectionby a value AD : 3s.
As a result the number of reflectionsin each set increases
from 4 to 6. To seeall ofthem separately,sufficient resolution is needed.Otherwisethe closepairs
of reflectionsappear to be single reflectionsand give
the impression of a monoclinic structure. It is easy
to show that for any p : q/3 + 6 a complete coincidence of these reflections takes place if s : 46,
where D may be both ) and ( 0. The heightsof the
second ellipse reflectionsgive a reliable q value and
an apparent valuep' : S/3 - d', where6' : 26. Both
by positions and intensities,the singlereflectionsl3/,
l3l, 131,13/seem
to be "monoclinic" 201and the coin-
ciding reflectionsof the setsseemto be "monoclinic"
131,131,l3l,T3l (Zvyagin et al, 1972).
The fact that only four reflections are distinguished
in a set on the second ellipse is not yet complete
evidenceon an exact coincidenceof the approached
reflections.Therefore further analysisof the patterns
s h o u l d b e b a s e do n t h e o u t e r r e f l e c t i o n sl 3 / , i . 3 . / + I
of the sets.These are single and their situations can
be measured with accuracy. Using the heights D of
these reflections, a more exact value q may be
calculated,for exampleby meansof the relationsq :
(D'd' * h.sr+1)/(21 + l). Thereupon measuring
the splitting of \kl,}klreflections adjacentto levelsD
* /4-this splitting is more pronounced for reflections
041,041
of the third ellipse-one may establishthe s
value as s : (Dom - Ds 1)/2k. With q and s known,
the value of p can be obtained by using the noncoinciding reflections of the second ellipse. Thus the
height difference AD of the outer reflections for each
set ofsix reflectionsis equal to q * 6s - 2p and hence
p:(q*6s-Lo)/2.
In such a way the following relationshave beenobt a i n e d p: : 0 . 2 9 7 q , 6 : - 0 . 0 3 6 Qs, : 0 . 0 1 6 q , s :
- 0 . 4 5 6 , t o w h i c h a u n i t c e l l c o r r e s p o n d sa: : 5 . 1 4 ,b
: 8 . 9 0 ,c : 1 4 . 1 5A , a = 9 0 o 3 3 ' , 0 : 9 6 " 1 2 ' , 7 :
90". This chlorite is thus triclinic and contains one
packet per repeat c. Low values for q and b as well as
the intensity relation of the reflectionsof the sixth
( 2 6 1 , 4 0 1a) n d s e v e n t h( 1 7 1 , 3 5 1 , 4 2 l e
) l l i p s e si n d i c a t e
that it may be di- or di,trioctahedral. In fact the
structural formula (Lio.?Alr,)r..(Alr.r.Feo'.5nFeo1fr)r
*
3u(OH)r.r,calculatedfrom the chem[Sisr8Alo.6r]o.ooro
ical analyses(Table 2), correspondsto cookeite with
a dioctahedral2:l layer (the degreeof octahedraloccupancy 1.99)and an almost trioctahedralhydroxide
interlayer sheet (the degreeof occupancy 2.8).
T,csl-B 2. Chemical Analysis of
Dialair Cookeite+
Wt
s102
a]-203
Fer0,
Fe0
LL20
per cent
uLL2v
i+
3e.25
44.28
1'3t
o.48
2,00
1 3 .o o
Total
99.33
*Analyst
R.l.Teleshova
COOKEITE FORMED BY BAUXITE ALTERATION
The Polytype ldentification
TAsr-s4. DistinguishingDiffraction Featuresof Three
of the Cookeite
According
to theintensities
of thesecond
elipse
reflections(Table 3), the structureof this cookeite
s rc
. sk
r se t lso | o
r i lnl Jl y Lt uhl E
cJ Uor n
fs rss fi .sb t usr o fppa a
r re euol rn
s -e
p a-upKa
s tc k e t f f i
| . , |\._o
"''.''i:f,::!iij.t iliit""ff||'tffi,:"f;0t"::,:'i:l''l'
D/,
p4-. D/n
';;'"
glt=i""k|\' o
p2 _
polytypesfrom di- and di,trioctahedral
hht ,ofgi\!,t,,r,ifl.ll:.T:"
satisfying the uniformity condition are possible,
namelylo'solilroroloio!|, lo,lo'sl
r1r- lo'so:rl,,lo'uo'ul
gg
r*r*lo'uo'ulwith correspondingsymmetry C2/n. C2, ;;;
Cf . b"fy the one with symm etry C2 has been rio
Trnrr 3. SecondEllipseReflectionsfor Trioctahedral
and Di,trioctahedral
Chloritesfrom Packets
lo'l at p/a : l/3, s: 0 andat p/q : l/3 0.036,
s/q = g.gru
lil
131
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3 21 ?:fr 2:ff2 A I r
',9
12 32
)L
1)
2:trfi
Z.1rZ
i:trZ
5
.7"
]I to
$
7
,
z
Z:EZ X II ,,
Z:r&
v'vr
2:fr i:S
"".ri G5
?
'
50
(Dritsand
amongthe naturalchlorites
recognized
'zvalues
Alexandrova, 1968, Table l). The [F[
55 calculated
usingthe first ellipse
for thesestructures
com-
1so
reflections-namely, lll,TTl,111,111,021,021-
2q
;;
l o i o i l r _ r _ l o i o i l , b u t i t s h o u l db e t a k e ni n t o a c c o u n t
that in this cases ( 0, a ( 90".
(Table4) indicatethat the
i'.2tr3trZfr);;; paredto thoseobserved
1.7F 29, 50 cookeitestudiedhas the triclinic (Cl) structure
i'.iTtr Zgl ?o (lo,,o1r*r*lo!p;1).Thesamestructureafter rotatll
e tion by 180'aroundtheb axiswouldhavea notation
i:?3?
Z:fi?
7.?2
4:tl,
i:23 1 ' 4 a z
7'75
s.22
e.ts
8.40
:
1.4?1i.+io ipt
3:ti
i:733 1?JI no
g:gi:i?iii ,i ."lJn,'Tffi'll1ff
;:ffit'"li'":"Ji",,"J"',
e.25 1.3@ 't2o-,1oo featuresof this polytype (Fig. 2) in the lessperfect
1,+O3
electrondiffracti,onoblique texturepatternsof ,o*"
?s/373 67 ilgi ii1i 29r ;11""'.'#:J':T
i:i:.Ts
#*,i:ili1i:'ff:,1?,::fjllJ"TH
1046
VRUBLEVSKAJA, DELITSIN, ZVYAGIN, AND SOBOLEVA
as a resultof the interactionof new Li-rich solutions
with pyrophyllite.
It should also be noted that the pyrophyllite
formednot only alongmacrojointsbut alsoinsidethe
bauxite mass along microslackeningzones (zones
wheremicrocracks-splits,clefts,fissures-areabundant). This is proved by the presenceof cookeiteadmixed with pyrophyllite in bauxite,though in this
casethe cookeiteis not so structurallyperfectas in
tectonicslackeningzones.Accordingto petrographic
and X-ray data,the emeryin the bauxitecontainsan
appreciableamount of hematiteand a small amounr
of corundum.On thesegroundsone can reasonably
suggestthat iron is essentially
absentin the processes.
Therebythe absenceof the noticeableisomorphous
replacementsof Fe for Al, that is natural for
pyrophyllite and cookeite,is observed.
References
BArLEy,S. W., rNo B. E. BnowN (1962)Chloritepolytypism:
I.
Regularand semi-randomone-layerstructures.Am. Mineral.
47,819-850.
BnrNoLnv,C. W., Brnvl OucsroN, nNn K. RosrlisoN(1950)
Polymorphismof the chlorites.L Ordered structures./cra
Crystallogr.3, 408-416.
rk,t6
BnowN,B. E., mlo S. W. BATLEv
(1963)Chloritepolytypism:
IL
Crystal structureof a one-layerCr-chlorite.Am. Mineral. 4t,
42-6t.
llr,rm
Dntrs, V. A , nro V. A. ALExANonovl(1968)Structureof
rto,!q
mineral from donbassitegroup-dioctahedral chlorite from
New Land. Mineral. Collect.Luou Uniu.22, 162-167.
-,
ANDE. K. LnsennNro(1967)Structurahy-mineralogical
featuresof donbassites.
Mineral.Collect.Luou Uniu.2l.40-48.
FIc. 2. Schemesof reflection distributions along the first (I) and
second (II) ellipsesofthe cookeite oblique texture pattern in cases Lrsrsn,JuorrHS., eNo S. W. Berlry (1967)Chloritepolytypism:
f V: Regulartwo-layerstructures.Am. Mineral. 52, 1614-1631.
o f p l q = / : , s : 0 ( a ) a n d p l q = 0 . 2 9 7 ,s l q : 0 . 0 1 6 ( b ) . T h e t i n e
MntulBsoN,
A McL., ,ANnG. F. Wllxrn (1954)Crystalstruclengths are taken proportional to F values; dotted lines indicate
ture of magnesium-vermiculite.
Am. Mineral. 39, 231-255.
theoretical positions of reflections not revealed experimentally.
Sutnozu,Hnnuo, tNn S. W. Berr-Ev(t966) Crystalstructureof
a two-layerMg-vermiculite.Am. Mineral 51, llZ4-1143.
geneticsignificanceof this di,trioctahedralchlorite SrrtNrrNx,H. (1958a)Thecrystalstructureofchlorite.I. A monoclinicpolymorph.Acta Crystallogr.
ll, l9l-195.
polytype.
(1958b)The crystalstructureof chlorite.IL A triclinic
The cookeitestudiedformedduringa latestageof
polymorph.Acta Crystallogr.14, 198-199.
bauxite transformation, reconstructedas follows. ZvyecrN, B. B. (1963)The theory of chloritepolymorphism.
Followingmetamorphicand, later, tectonicaction,
Kristallografya, 8. 12-38.
(1967)Electron-Difraction Analysisof Clay Mineral Structhe bauxitestratadevelopedlocal zonesof intensive, tures. Plenum Press,New York
fine jointing. Silica-rich solutions circulated along
-,
K. S MrsurNro, exo S. V. SogoI-eve
(1968)The structhesefine joints and reactedwith the aluminaof the
tures of phyrophilliteand talc in the tight of polytypismof
bauxite to form pyrophyllite. The formation of
micalike minerals.Kristallografiya, f3, 599-604.
pyrophyllite may indicate that rather high p,Z -,
A. F. Feoorov, S. V. Sosor-Bve,
luo K. S. MlsurNxo
parametersexistedduring the mineral genesisand
(1972)The reflectionofmonoclinicangleoflayer silicatesin the
electron diffraction oblique texture patterns. Kristallografiya,
also that alkalinecationswereabsentfrom the solur7.851-853.
tions. The formation
"il
of the structurally perfect
di,trioctahedralchlorite cookeite occurred in the
zonesof later tectonicshearsin the pyrophyllitemass
Manuscript receiued,August 29, 1974;accepted
for publication,April 28, 1975.
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