x ray in illite
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8/15/2019 X RAY in Illite
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Clays and Clay Minerals Vo l . 3 2 No . 5 3 3 7 -3 4 9 1 9 8 4 .
X R A Y P O W D E R D I F F R A C T I O N I D E N T IF I C A T I O N
O F I LL I T I C M A T E R I A L S
JAN SRODON
Polish Academy of Sciences, Institute of Geological Sciences
31-002 Krakow, Senacka 3, Poland
Abstract--The 10-/~ clay components of sedimentary rocks ("iUites") are commonly mixtures of 100%
nonexpandable illite and an ordered illite/smectite mixed-layer mineral. If the proportion of the illite/
smectite in a mixture is sufficient to produce a measurable reflection between 33-35*20 (CuKa radiation)
that is noncoincidentwith an illite reflection, the ratio of component layers and type of interstratification
for the mixed-layer mineral can be determined. The identification technique developed in this study rests
upon the following experimental findings for ordered illite/smectites of diagenetic origin: (1) the thickness
of the illite layer in illite/smectites is 9.97/~; (2) the thickness o f smectite-ethylene glycol complex ranges
from 16.7 to 16.9/~; (3) illite/smectites form a cont inuous sequence ofinterstratification ypes--random,
random/IS, IS, IS/ISII, ISII- -and each type is related to a specific range of expandability.
The new technique broadens the computer simulation method developed by R. C. Reynolds and J.
Hower to include those sedimentary materials which are dominated by the presence of discrete illite, are
low in illite/smectite, and, as such, have been described previously only by an " illite crystallinity index."
Key Words--Diagenesis, Identification, Illite, Illite/smectite, Interstratification.
INTRODUCTION
The name "illite" was introduced by Grim e t a l in
1937 "as a general term for the clay mineral constit uent
of argillaceous sediments belonging o the mica group."
Since that time, the term has been widely used in this
broa d sense to designate material giving a ~ 10/k re-
flection on X-ray powder diffraction patterns of clay-
size fractions of sediments and soils. Hence, "illit e" is
now used as a group n ame, covering a range of chemical
compositi ons and structural characteristics. The struc-
tural variabi lity ofillite was quantifi ed by W eaver (1960)
in terms of "iUite crystallinity" which was based on
the "sharpness" of the 10-/~ peak. The method has
been used extensively, especially in Weste rn Europe,
for studying deep diagenesis and low-grade meta mor-
phi sm (see, e.g., Kisch, 1983). It has neve r been estab-
lished precisely what ph eno men on gives rise to differ-
ent illite "crystallinities."
The n ature of illite was approached from the struc-
tural standpoint by Gaudette e t a L (1966). Am on g five
well-known illite reference samples, they found one
pure and nonexpanding. The other four contained
mixed-layer expandable material: illite com mon ly ap-
peared to be a physical mixture of minerals. This in-
terpretation was confirmed later by Heller-Kallai and
Kalman (1972) and ~rodofi (1979). From an investi-
gation of a range of mixed-layer illite/smectites and
illites, Hower an d Mowatt (1966) concluded that "il-
lites represent one mineralogical end m emb er of the
'Currently an exchange scientist at the U.S. Geological
Survey, Federal Center, Denver, Colorado 80225.
Copyright 9 1984, The Clay Minerals Society
montmorillonite-mixed-layer-illite roup and re main
distinct from true micas un til the beginni ng of meta-
morp hism ." This phrase may serve as a definition of
the mineral illite, in contrast to the use of the term
"illite" in the broad sense, but it does not solve the
problem of illite identification. In the following con-
siderations, "illite" refers to the 100% nonexpan ding
mineral, and "illitic material" is used as a group nam e
implyin g the possible presence of some expandable
layers.
Reynolds and Hower (1970) published a computer
method for investigating mixed-layer illite/smectites
and defined three types o f interstratification of com-
ponent layers: random, IS-ordered, and ISII-ordered,
where I = illite layer, S = sm ectite layer. Ran do m in -
terstratification was defined by lack of in teraction be-
tween adjacent layers: the probabili ty of finding an illite
layer following a smectite layer in a specified but ar-
bitrary direction simply equals the pro bability of find-
ing an illite layer in the sequence
pS.I = pI.
IS-ordering was defined as a nearest-neighbo r inter-
action; the probability of illitc following smectite is
higher than in the rando m case. Maxi mu m IS-ordering
implies that all smectitc layers are followed by illite
layers:
pS. I = 1 (prov iding pI -> 0.5).
It should be stressed that, according to the definition
of Reynolds and Hower (1970), maximum ordering
does not require a l: l composition . A miner al with
such a composition (pI = pS = 0.5) is only a special
337
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338
Srodofi
lays and lay Minerals
Table 1. X-ray pow der diffraction data for ordered illite/smectites and othe r illitic materials.
Reflections
from air-dry Type of
Reflections from glycolated preparations Aoo2.0o~ BBI2 BB22 preparations illitie
Sample (~ CuKtx adiation) (~ (*20) (~ (~ Ir2 %S materiaP
1 5.99 9,84 16.39 26.56 32.91 43,81 47.38 6.55 49 R/ IS
2 6.00 9.79 16.42 26.52 32.87 43.80 47.27 6.63 48 R/ IS
3 6.64 9.98 16.72 26.88 44.41 48,01 6.74 48 IS
4 6.44 9.73 16.51 26.57 33.38 44.00 47.20 6.78 44 R/ IS
5 6.58 9.66 16.67 26.63 33.49 44.14 47.07 7.01 39 R/ IS
6 6.64 9.63 16.69 26.62 33.49 44.09 47.16 7.06 7.93 37 IS
7 6.58 9.59 16.66 26.58 33.42 44.07 47.08 7.07 8.48 38 R/I S
8 6.64 9.51 16.69 26.58 33.39 44.02 46.99 7.18 8.50 36 IS
9 6.08 9.50 16.74 26.73 33.33 44.36 sh 7.24 38 R/ IS
10 6.89 9.57 16.82 26.67 33.62 44.26 46.93 7.25 32 IS
11 6.71 9.46 16,80 26.65 33,59 44.36 46.90 7.34 32 IS
12 6.75 9.46 16.92 26,75 33.86 44.57 sh 7.46 5.0 4.8 29 IS
13 6.69 9.40 16.86 26.62 33.58 44.29 sh 7.46 8.18 28 IS
14 6.91 9.34 17.00 26.75 33.88 44.65 sh 7.66 5.0 4.0 25 IS
15 7.14 9.28 17.07 26.68 33.98 44.64 46.24 7.79 4.6 4.8 8.16 18.05 3.78 20 IS/ ISI I
16 7.13 9.26 17.09 26.73 34.09 44.73 sh 7.83 4.8 5.0 20 IS/ ISI I
17 7.61 9.26 17.17 26.69 34.56 44.66 46.29 7.91 3.8 3.8 8.20 17.60 4.48 17 ISII
18 7.28 8.94 17.27 26.77 34.30 45.02 -- 8.33 4.6 5.0 15 IS/ ISI I
19 7.51 8.98 17.32 26.78 34.74 45.08 -- 8.34 4.6 4.6 13 IS/ ISI I
20 sh 9.06 17.44 26.79 34.93 45.18 -- 8.38 3.6 3.8 8.55 17.86 2.38 9 ISII
21 sh 9,05 17.47 26.81 35.08 45.11 -- 8.42 3.3 2.8 8.49 17.87 2.32 9 ISII
22 7.30 8.96 17.52 26.79 33.85 45.47 -- 8,56 4.9 5.2 8.28 2.61 26 IS + I
23 -- 8.94 17.52 26.81 35.1 45.41 -- 8.58 3.6 4.0 8.47 2.02 7 ISt I
24 -- 8.96 17.56 26.78 34.9 45.2 6 -- 8.60 3.2 2.6 8.63 17.86 1.52 6 ISII
25 sh 8.86 17.56 26.78 34.9 45.26 -- 8.68 3.6 4,0 8.47 2.46 9 ISII + I
26 -- 8.84 17.74 26.87 35.0 45.59 -- 8.90 3.6 2.8 8.59 17.94 1.83 8 I + ISI I
27 -- 8.85 17.76 26.85 -- 45.53 -- 8.91 3.3 3.0 8.72 17.83 1.58
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Vol. 32, No. 5, 1984 X-ray pow der dif f ract ion identif icat io n of i l l i te 339
c a s e o f m a x i m u m I S o rd e r i n g , a c a s e i n w h i c h t h e r e
a r e n o e x c e ss i l l it e la y e r s. T h i s e x c e p t i o n a l t y p e o f o r -
d e r i n g s h o u l d b e c a l l e d r e g u la r , a c c o r d i n g t o t h e d e f i-
n i t i o n s o f A I P E A N o m e n c l a t u r e C o m m i t t e e ( B a il e y et
aL
1 9 8 2 ). S u c h a m i n e r a l h a s , o f c o u r s e , b e e n f o u n d
i n n a t u r e , a n d i s c a l l e d r e c t o r i t e ( B a i l e y
et aL
1982) .
M a x i m u m I S I I t y p e o f o rd e r i n g w a s d e f in e d b y
R e y n o l d s a n d H o w e r ( 1 9 7 0 ) a s t h e p r o b a b i l i t y o f a
s m e c t i t e l a y e r b e i n g f o l l o w e d b y t h r e e i l l i t e l a y e r s
e q u a l i n g 1 :
p S . I I I = 1 .
F o r t h i s a r r a n g e m e n t t o b e p o s s i b l e , p I > 0 . 7 5. I f p I
= 0 . 7 5 , n o e x c e s s i l l i t e l a y e r s e x i s t i n t h e m i n e r a l , a n d
t h e m i n e r a l i s a r e g u l a r i n t e r s t ra t i f i c a t i o n . S u c h a m i n -
e r a l w i t h n e a r l y p e r f e c t I S I I i n t e r s t r a t i f i c a t i o n h a s b e e n
n a m e d t a r a s o v i t e (L a z a r e n k o a n d K o r o l e v , 1 9 7 0 ;
B r i n d l e y a n d S u z u k i , 1 9 8 3 ).
A c o m p l e t e s t a t is t i c a l t r e a t m e n t o f m i x e d - l a y e r i n g
c a n b e f o u n d i n R e y n o l d s ( 1 9 80 ) . I n a n a l t e r n a t i v e a n d
a l so w i d e l y u s e d m a t h e m a t i c a l a p p r o a c h t o m i x e d - l a y -
e r i n g ( K a k i n o k i a n d K o m u r a , 1 9 6 5) , t h e a b o v e - l i s t e d
t y p e s o f i n t e r s t r a t i f i c a t i o n a r e a l s o r e c o g n i z e d a n d c a l l e d
R e i c h w e i t e 0 , 1 , a n d 3 , r e s p e c t i v e l y .
I n 1 98 0 , S ro d o f i p u b l i s h e d a n i m p r o v e m e n t o f t h e
R e y n o l d s a n d H o w e r m e t h o d , t a k i n g in t o a c c o u n t th e
v a r i a b l e t h i c k n e s s o f e t h y l e n e g l y c o l - s m e c t i t e c o m p l e x .
T h e s m e c t i t i c e n d o f t h e m i x e d - l a y e r e d s e ri e s w a s w e l l -
d o c u m e n t e d i n t h e p a p e r , b u t t h e i l l it i c e n d w a s n o t
b e c a u s e o f a l a c k o f s a m p l e m a t e r ia l . T h e a s s u m p t i o n
o f a 1 0 - ,~ - t h ic k i ll i t e l a y e r w a s m a d e a c c o r d i n g t o
R e y n o l d s a n d H o w e r ( 1 9 7 0 ), w i t h o u t v e r i fi c a t i o n . T h e
o b j e c t i v e s o f t h e p r e s e n t p a p e r a r e t o i n v e s t i g a t e t h e
i l l it i c e n d o f t h e m i x e d - l a y e r e d s e ri e s u s i n g a b r o a d
r a n g e o f s a m p l e m a t e r i a l , a n d t h e n t o a p p l y t h e s e d a t a
f o r i d e n t i f i c a t i o n o f o t h e r i l l i t i c m a t e r i a l s .
X - R A Y D I F F R A C T I O N D A T A F O R
I L L I T I C M A T E R I A L S
T h e s a m p l e s a n a l y z e d i n t h i s st u d y c o m e f r o m s e v -
e r a l l o c a l it i e s i n E u r o p e a n d t h e U n i t e d S t a t e s a n d
r e p r e s e n t d i f f e r e n t a g e s a n d s e d i m e n t a r y f o r m a t i o n s
( T a b l e 1 ). A l m o s t a l l a r e o f d i a g e n e t i c o r ig i n . T h e a n -
a l y t i c a l t e c h n i q u e s u s e d a r e i d e n t i c a l t o t h o s e d e s c r i b e d
b y S r o d o f i (1 9 8 0 ). A l l s a m p l e s w e r e N a - e x c h a n g e d a n d
e x a m i n e d b y X - r a y p o w d e r d i ff r ac t io n (X R D ) a t r o o m
h u m i d i t y ( 4 0 - 5 0 % R H ) . A l l p e a k p o s i t io n s w e re o b -
t a i n e d b y s t e p - s c a n n i n g a t 0 .0 1 2 0 i n t e r v a l s u s i n g C u K a
r a d i a t i o n .
C o m p u t e r - s i m u l a t e d , o n e - d i m e n s i o n a l X R D p a t -
t e r n s o f h i g h l y i l li t ic m i x e d - l a y e r i l l i t e / s m e c t i t e s w e re
i n s p e c t e d i n t h e r a n g e o f 5 0- 3 * 2 0 i n s e a r c h f o r th e
p a r a m e t e r s m o s t s e n si t iv e t o t h e c o m p o n e n t l a y e r r a -
t i o . I n a d d i t i o n t o X R D p e a k p o s i t i o n s f o r e t h y l e n e
g l y c o l - s o l v a t e d p r e p a r a t i o n s , t h e f o l lo w i n g m e a s u r e -
m e n t s a l s o w e r e f o u n d t o b e u s e f u l:
1 ) Aoo2-ool= t h e a n g u l a r d i s t a n c e b e t w e e n t h e 0 0 2
a n d 0 0 1 r e f le c t i o n s f r o m g l y c o l a t e d p r e p a r a t i o n s ( t h e
1 M m i c a i n d i c e s a r e u s e d h e r e a n d h e r e a f t e r t o d e s -
i g n a t e t h e r e f l e c t io n s o f i l li t ic m a t e r i a l a p p r o x i m a t e l y
c o i n c i d i n g w i t h t h e r e f l e c ti o n s o f m i c a ; t h e n o n c o i n -
c i d e n t r e f l e c ti o n s a re d e s i g n a t e d b y t h e i r a n g u l a r v a l -
ues ) ;
( 2) P o s i t i o n s o f th e 0 0 1 a n d 0 0 2 r e f l e c t io n s f ro m
a i r - d r y p r e p a r a t i o n s ;
( 3 ) I r = t h e i n t e n s i t y r a t i o s ( p e a k h e i g h t s r a t i o s ) o f
t h e 0 0 1 a n d 0 0 3 r e fl e c t io n s f r o m t h e a i r - d r y a n d t h e
g l y c o l a t e d s a m p l e s :
0 0 1 / 0 0 3 a i r - d r y
I r =
0 0 1 / 0 0 3 e t h y l e n e g l y co l
( 4) B B 1 = t h e j o i n t b r e a d t h o f 00 1 i l l it e a n d a d j a -
c e n t i l l i t e /s m e c t i t e r e fl e c ti o n s , m e a s u r e d i n ~ f r o m
w h e r e t h e t a i l s o f t h e p e a k j o i n t h e X - r a y b a c k g r o u n d ;
( 5) B B 2 = t h e j o i n t b r e a d t h o f 0 0 4 i l l i t e a n d a d j a -
c e n t i U i t e / s m e c t i t e r e f l e c ti o n s , m e a s u r e d l i k e B B 1 .
T h e l a s t t w o p a r a m e t e r s w e r e d i s c u s s e d b y S r o d o f i
( 1 97 9 ). T a b l e 1 p r e s e n t s t h e a b o v e d a t a f o r m o s t o f
t h e s a m p l e s u s e d i n t h i s s t u d y . T h e l a s t t w o c o l u m n s
i d e n t i f y t h e i l l it i c m a t e r i a l s b y m e t h o d s d e v e l o p e d i n
t h i s s t u d y .
T H I C K N E S S O F T H E I L L I T E L A Y E R A N D T H E
R E F I N E D T E C H N I Q U E F O R I D E N T I F Y I N G
O R D E R E D I L L I T E / S M E C T I T E S
T h e s a m p l e s i n T a b l e 1 a r e a r r a n g e d i n t o t w o g r o u p s :
i l l i te / s m e c t i t e s o r i ll i ti c m a t e r i a l s d o m i n a t e d b y i U i te /
s m e c t i t e ( 1 - 2 5 ) , a n d i l li t e s o r i l l i ti c m a t e r i a l s d o m i -
n a t e d b y i l li t e ( 2 6 - 4 1 ) . F r o m e t h y l e n e g ly c o l - t r e a t e d
p r e p a r a t i o n s , t h e f i rs t g r o u p i s
characterized
b y a n o n -
i n t e g r a l s e r i e s o f b a s a l r e f l e c t i o n s a n d a A o o 2- oo l v a l u e
o f 8 . 85 - 9 .0 0 * 2 0 ; t h e s e c o n d g r o u p i s c h a r a c t e r i z e d b y
a n i n t e g r a l s e r i e s o f b a s a l r e f l e c t i o n s a n d a A oo2-o oxv a l u e
s m a l l e r t h a n 8 .7 * 20 .
S a m p l e s i n t h e s e c o n d g r o u p ( w h e n t h e 2 0 v a l u e s i n
T a b l e 1 a r e c o n v e r t e d i n t o d - s p a c i n g s ) i n d i c a t e t h a t
t h e l a y e r s p a c i n g o f d i s c r e t e i l l i t e i s n o t s t r i c t l y I 0 Zk,
b u t v a r i e s f r o m 9 . 9 6 t o 1 0 .0 3 A . T h e m o s t p r e c i s e v a l u e
c a n b e o b t a i n e d f r o m t h e 0 0 3 a n d 0 0 5 r e f l e c ti o n s b e -
c a u s e t h e 0 0 1 a n d , t o a l e s s e r e x t e n t t h e 0 0 2 , a r e d i s -
p l a c e d s l i g h t ly to w a r d l o w a n g l e s d u e t o t h e e f f ec t o f
s m a l l c r y s t a l li t e s i ze a n d t h e L o r e n t z p o l a r i z a t i o n f a c -
t o r ( R e y n o l d s , 1 9 6 8 ). T h e q u e s t i o n t h e n a r i s e s , i s t h e
i l li t e l a y e r t h ic k n e s s i n t h e m i x e d - l a y e r m i n e r a l s a l s o
a s v a r i a b l e ?
T h i s q u e s t io n c a n b e a n s w e r e d b y p l o t t in g t h e d a t a
f r o m T a b l e 1 i n t o F i g u r e 8 o f S r o d o f i (1 9 8 0 ) . F i g u r e 1
s h o w s t h e r e s u l t s . M o s t s a m p l e s f r o m t h e i l l i t e - d o m -
i n a t e d g r o u p p l o t w i t h i n t h e o r e t i c a l l i n e s r e p r e s e n t i n g
i ll i te , c o m p u t e d a s s u m i n g b o t h i n f i n it e t h i c k n e s s f o r
t h e c r y s t a ll i te s , a n d 7 - 1 4 l a y e rs . T h e r a n g e o f la y e r
t h i c k n e s s f o r d i s c r e t e i l l it e i s d e a r l y s h o w n . A f e w p o i n t s
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3 4 0 S ro d o f i
lays and lay Minerals
o 2 g
17,8
1 7 6
I Z /
17.2
17.0 -
16.8 -
16.6
16.4
4 :
9 " , .o / o 20
~ . o ~ ' ~ J 1 7.8
o . 9 t e y ) e l ~ / /
T §
17.4
e §
3 *
17.2
16.9 ~ 16.7A
I I I I I I I
2 7 . 0
0 2 0
17.0
2 6 . 4 2 6 . 6 2 6 . 8
F ig u re 1 . P lo t o f 0 0 2 v s . 0 0 3 r e f l e c t io n s o f i l l i t i c m a te r i a l s .
S o l id c i rc l e s = s a m p le s d o m in a te d b y i l l i te ; o p e n c i r c l e s a n d
c ro s s e s = s a m p le s d o m in a te d b y i l l i t e / s m e c t i t e c ro s s e s r e p -
re s e n t d a t a f ro m th e l i t e r a tu re a n d a re n o t l i s t e d in T a b le 1 ).
P a i r s o f s o l i d a n d d a s h e d l i n e s = t h e o r e t ic a l p l o ts o f o r d e r e d
i l l i te / s m e c t i t es w i t h v a r i o u s c o m b i n a t i o n s o f c o m p o n e n t l a y e r
th i c k n e s s. S o l id l i n e s m a rk e d w i th o o a n d 7 -1 4 = th e o re t i c a l
p lo t s o f i l l i t e w i th a n in f in i t e c ry st a l l i t e t h i c k n e s s a n d 7 -1 4
la y e r s in c ry s t a l l i t e s . H y d ro th e rm a l s a m p le s : T i s f ro m L a -
z a r e n k o a n d K o r o l e v 1 9 7 0) ; P i s f ro m G a l l e g o a n d P 6 r e z
1965); 3 is Ark ansas rec to r i t e Tab le 1 , no . 3 ) ; N is f rom
S h i m o d a 1 9 7 2 ) .
p l o t t i n g r a n d o m l y a b o v e t h e i n f i n i t e t h i c k i l l it e l i n e
w e r e f o u n d to r ep r e s e n t s a m p l e s c o n t a m i n a t e d w i t h
q u a r t z , i n w h i c h t h e q u a r t z 1 01 r e f l e c t i o n i n t e r f e r e d
1 6 8
1 6 . 6
1 6 . 4
I I I i I I
. o o _
1 0
15
2 0
3 0
4 0
i 0
l , I I I I I
2 6 . 4 2 6 . 6 2 6 . 8 2 7 0 o 2 0
F ig u re 2 . P lo t fo r d e t e rm in in g s m e c t i t e : i l l i t e r a t io f ro m 0 0 2
a n d 0 0 3 r e f l e c t io n s in o rd e re d i l l i t e / s m e c t i t e s o f d i a g e n e t i c
o r i gi n , b a s e d o n t h e c o m p u t e r d a t a o b t a i n e d w i t h t h e f o l l o w -
in g a s su m p t io n s : 7 -1 4 l a y e r s / c ry s ta l l i t e , i l l i t e l a y e r = 9 . 9 7
th ic k , s m e c t i t e -e th y le n e g ly c o l l a y e r = 1 6 . 7 -1 6 . 9 /~ th i c k . S o l -
id l i n e s = IS ty p e o f o rd e r in g ; d a s h e d l in e s = IS I I t y p e o r -
derirtg.
w i t h t h e 0 0 3 o f i l l i t e a n d d i s p l a c ed t h e p r o j e c t i o n p o i n t
t o w a r d s t h e l e f t s i d e o f t h e f i g u re .
W i t h t h e e x c e p t i o n o f s a m p l e s 2 2 a n d 2 5 , al l s a m p l e s
f r o m t h e i l l i t e / s m e c t i t e - d o m i n a t e d g r o u p a r e p u r e i l-
l i t e / s m e c t i t e s . T h e c r i t e r i a f o r m a k i n g t h i s d i s t i n c t i o n
a r e d i s c u s s e d b e l o w . I n F i g u r e 1 , a l l o f t h e s e s a m p l e s
p l o t a s a s e q u e n c e o f d e c r e a s i n g e x p a n d a b i l i t y t h a t e x -
t r a p o l a t e s t o la y e r th i c k n e s s s m a l l e r t h a n 1 0 / k f o r t h e
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Vol. 32, No. 5, 1984 X-ray powder diffraction identification of illite 341
o
16.9A
ILLITE
9.97~
35.92
ISll ~E
36.00
34.56
5 S
10
15
20
.35 .96
IS
10
15
35.90
67A
I I I 1 t l ] [ ] l l l f l t l l l T F l [ I I I I I I I I I l I l [ l l l l l l l l
35.93 No.16
34.86 tl
3 4.7 3 x ~ . . . . ~ _ x _ ~
I l l l l l l l ] l l l i l l l i i ] i l I i i [ l l l l l l i l l l l l [ [ l l l
1 20 ~ 0 ~ 5 ~ 2 ~
33.75 34.14
33.60 33 92
i ~ 3O i ~
Figure 3. Diffraction profile, 31-37"20, highly iUitic illite/
smectites calculated for 9.97-/~, illite layer and various com-
bina tions of ordering and thickness for the smectite-ethylene
glycol layer. BB2 parameter corresponds to the angular dis-
tance between ~ 37028 and the vertical line. The dependence
of BB2 on the type of ordering is clearly shown. 10% S IS-
ordered minerals and 20% S ISII-ordered minerals are the-
oretical examples; in nature he type of ordering changes around
15% S (of. Figures 4 and 9).
illite layers. It was found by trial an d error that all data
points for diagenetic, ordered illite/smectites with 70%
or more illite layers can be match ed by a comb ina tio n
of the layer thicknesses of 9.97/~ for the illite layer
an d from 16.7 to 16 .9/~ for the ethylene glycol-smec-
tire layer (Figure 1).
Samples T, P, 3, and N are of hydrothermal origin
and are plotted in Figure 1 to show that the above
findings about the layer thicknesses are valid only for
Figure 4. Examples of X-ray powder diffraction patterns of
glycolated, ordered illite/smectites. Sample numbers refer to
Table 1, where the peak positions are listed. Type of ordering,
percentage of smeetite, and manner of measuring BB1 and
BB2 parameters are shown. Samples 15 and 16 have identical
expandabilities, but different thicknesses of the smectite-eth-
ylene glycol complex. The difference manifests itself most
strongly in the relative intensities of peaks in the 42-48~
region.
the materials of diagenetic origin. Amon g the hydro-
thermal samples the variat ion is much broader, an d it
remains to be shown whether the variation is due to
changes in illite or ethy lene glycol-smectite layer thick-
ness or both.
It is fortunate for identification that the range of
thicknesses of smectite-ethylene giycol complexes i n
diagenetic, ordered illite/smectites is so narr ow and
that the illite layer thickness is stable. By contrast, in
smectite-do minated, diagenetic, mixed-layer minerals,
the thickness of the smectite-ethylene glycol complex
ranges from 17.2 to 16.6 ~ (Srodofi, 1980).
A plot laased on Fig ure 1 an d cali brated for the per-
centage ofsmectite layers with the co mputer-calculated
data (Figure 2) serves for precise mea sure ment of the
illite/smectite ratio i n highly illitic mixed-layer mi n-
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Table 2 . Exam ples of the com ple te compu te r f i t o f X - r ay pow d er d i f fr ac t ion pa t te r ns of g lycola ted i l l i t e / smec t i t e s?
Peak pos i t ions
S a m p l e p a r a m e l e r s * 2 0, C u K a r a d i a t io n )
Sam ple 15 20 S , IS/IS I I 16.9/~ 7.14 9.28 17.07 26.68 33.98 44.64
T 20 S, ISII 16 .9/9 .97 /k 7.58 9.20 17.10 26.69 34.56 44.64
T 20 S, IS 16.9/9.97/~ 6.76 9.17 17 .0 7 26.68 33.75 44.67
Sam ple 17 17 S , ISI I 16.9 /k 7.61 9.26 17 .1 7 26.69 34.56 44.66
T 20 S, ISI I 16.9/9.97 A 7.58 9.20 17.10 26.69 34.56 44.64
T 15 S, ISII 16.9/9.97 ~ 7.71 9 .09 17.22 26.72 34.68 44.81
Sam ple 20 9 S, ISII 16.8 ~ sh 9.06 17.44 26.79 34.93 45.18
T 10 S , ISI I 16.9/9 .97/~ 7.91 8.94 1 7. 39 26.75 34.86 45.10
T 10 S, ISII 16.7/9.97 ~ 7.97 8.95 17.44 26.83 35.09 45.19
46.24
46.40
46.21
46.29
46.40
46.21
sh = shoulder .
i Sample nu mber s and ident i f i ca tion (the pe r centage of smee t i t e , the type o f o r de ring , the th ickness of smee t i t e - e thy lene
glycol complex) a r e f r om Table 1 and F igur e 1 . The ex per imenta l va lues , except o f the r e f lec t ion a t abo ut 9*20 ( see tex t ), f i t
w i th in the r ange g iven by the theor e t ica l da ta ( T).
a g r e e s w i t h t h e p o s i t i o n r e l a t i v e t o t h e I I S l i n e . T h u s ,
s a m p l e 1 7 is a n a l m o s t p e r f e c t ly o r d e r e d I S I I s t r u c t u re
( s e e a l s o T a b l e 2 ).
T h e t h i c k n e s s o f s m e c t i t e - e t h y l e n e g ly c o l c o m p l e x
o f s a m p l e 1 9 is 1 6 . 7 5 / ~ ( F i g u r e 1 ). I f t h e s a m p l e w a s
a n I I S st r u c tu r e , i t s h o u l d p l o t i n F i g u r e 5 j u s t t o t h e
l e f t o f t h e I I S l in e , b u t t h a t i s n o t t h e c a s e . T h e a l t e r -
n a t i v e e x p l a n a t i o n i s t h a t s a m p l e 1 9 is a n i n t e r m e d i a t e
I S / I S I I s t r u c t u re ( i n c o m p l e t e l y o r d e r e d I S I I s t r u c tu r e ) .
F i g u r e 5 s h o w s t h a t a o n e - h a l f - o r d e r e d I S I I s tr u c t u r e
p l o t s e x a c t l y o n t h e I I S l i n e. S a m p l e 1 9 is t h e r e fo r e a n
a p p r o x i m a t e l y o n e - h a l f - o r d e r e d I S I I st r u c tu r e .
S a m p l e s A -2 , F , a n d G o f R e y n o l d s a n d H o w e r
( 1 9 70 ) , i n t e r p r e t e d a s I I S s t ru c t u r e s b y D r i t s a n d S a -
l d a a r o v (1 9 7 6 ) , p l o t i n F i g u r e 5 i n t h e f i e ld o f p e r f e c t
o r a l m o s t p e r f e c t I S o r d e r i n g , a s i d e n t i fi e d b y t h e o r i g -
i n a l a u t h o r s . T h e v a l u e o f th e 3 3 -3 5 * 2 0 r e f l ec t i o n w a s
g i v e n b y R e y n o l d s a n d H o w e r ( 1 9 70 ) o n l y f o r s a m p l e
A - 2 a n d c o n f i r m s t h e i n t e r p r e t a t i o n o f p e rf e c t IS o r -
d e r i n g . T h u s , f r o m t h e a b o v e d a t a t h e I I S t y p e o f o r -
d e r i n g d o e s n o t s e e m t o e x i s t i n d i a g e n e t i c i l li t e / s m e c -
r i te s . A s i m i l a r c o n c l u s i o n w a s r e a c h e d b y S c h u l t z ( 1 9 8 2 )
i n h i s s tu d y o f c l a y s f r o m t h e M o n t a n a D i s t u r b e d B e l t .
I n t h e c o m p o s i t i o n a l r a n g e 5 0 - 4 0 , a l l v a r i e t i e s o f
i n t e r s t r a ti f i e a t io n w e r e e n c o u n t e r e d f r o m c o m p l e t e l y
r a n d o m t o m a x i m u m I S - o r d e r e d ( F ig u r e 5). P a rt i a ll y
o r d e r e d I S s t r u c t u r e s w e r e f o u n d d o w n t o a b o u t 3 0
S , a n d m a x i m u m - o r d e r e d d o w n to 20 S . B e t w e en 2 0
a n d 1 2 S p a r t i a l l y o r d e r e d I S I I s t r u c tu r e s w e r e e n -
c o u n t e re d . A m o n g t h e m a x i m u m - o r d e r e d I S I I s a m p l e s
k n o w n to t h e a u t h o r , th e m o s t e x p a n d a b l e i s 1 7 S
a n d t h e m o s t i l l i t i c i s 6 S .
F i g u r e 5 c a n b e u s e d t o c h e c k t h e i d e n t i f i c a t i o n o f
t h e t y p e o f i n t e r s tr a t i f ic a t i o n b a s e d o n B B 1 o r B B 2 .
F o r t h e i n t e r m e d i a t e I S / I S I I s tr u c t u re s , i n t e r p o l a t i o n
b e t w e e n t h e a p p r o p r i a t e l i n e s i n F i g u r e 2 c a n b e a p p l i e d
t o i n c r e a s e t h e p r e c i s i o n o f t h e d e t e r m i n a t i o n .
T a b l e 2 p r e s e n t s a v e r i f ic a t i o n o f t h e d e s c r i b e d i d e n -
t i f ic a t i o n t e c h n i q u e b y a c o m p l e t e c o m p u t e r f it w i t h
t h e X R D p a t t e r n s o f th r e e s a m p l e s fo r th e 3 - 5 0 * 20
r a n g e. I t a p p e a r s t h a t a l l t h e r e f le c t i o n s c a n b e m a t c h e d
s a t i sf a c t o r il y , e x c e p t f o r 0 0 1 , w h i c h i s a l w a y s d i s p l a c e d
i n t h e s i m u l a t e d p a t t e r n s t o w a r d l o w e r a n g l e s . T h i s
d i s c r e p a n c y i s i n t e r p r e t e d a s t h e e f f ec t o f s m a l l p a r t i c l e
s iz e , w h i c h i s m o s t s tr o n g l y m a n i f e s t e d i n 7 -1 0 ~ r e -
g i o n ( R e y n o l d s a n d H o w e r , 1 9 70 ). T h e s i m u l a t i o n s
w e r e m a d e a s s u m i n g a n e v e n d i s t r i b u t i o n o f c ry s t a l li t e s
f r o m 7 t o 1 4 l a y e r s t h i c k . T h e p e a k p o s i t i o n i s c o n -
t r o l l e d b y t h e n u m b e r o f la y e r s in t h e t h i c k e s t c r y s t a l -
l i te s (S r o d o fi , u n p u b l i s h e d d a t a ) . I t i s c o n c l u d e d t h e
h i g h l y i l li t i c m i x e d - l a y e r m i n e r a l s o f d i a g e n e t i c o r i g i n
h a v e t h e i r t h i c k e s t c r y s t a l l i t e s l a r g e r t h a n 1 4 la y e r s .
N e v e r t h e l e s s , t h e 7 - 1 4 - l a y e r s m o d e l i s s a ti s f a c t o r y f r o m
t h e i d e n t i f i c a t io n s t a n d p o i n t ( c o a r s e r c r y s t a l l i te s a r e
v e r y c o s t l y t o s i m u l a t e ) b e c a u s e f o r s u c h l a r g e c r y s ta l -
l i te s th e d i s p l a c e m e n t s o f h i g h e r a n g l e p e a k s a r e n e g -
l ig i b le . T h e 1 - 8 - l a y e r m o d e l , u s e f u l w h e n d e a l i n g w i t h
t h e s m e c t i t e - d o m i n a t e d m i x e d - l a y e r m i n e r a l s ( S r o d of i ,
1 9 8 0 , 1 9 8 1 ) , i s n o t v a l i d f o r t h e i l l i t i c o n e s . A m o n g
t h e d a t a p r e s e n t e d i n T a b l e 2 , t h e m o s t c o n v i n c i n g is
t h e g o o d f i t o f t h e r e f l e c t i o n a t 3 3 - 3 5 * 2 0 b e c a u s e t h i s
r e f le c t i o n is e x e p t i o n a l l y s e n s i ti v e t o t h e t y p e o f i n t e r -
s t r a ti f i c a ti o n a n d t o t h e t h i c k n e s s o f th e s m e c f i t e - e t h -
y l e n e g l y c o l c o m p l e x ( F i g u r e 3 ) .
P e a k i n t e n s i t y d a t a m a y a l s o b e u s e d t o v e r i f y t h e
i d e n t if i c at i o n p r o c e d u re . C o m p u t e r s i m u l a t i o n s h o w e d
t h a t t h e r e l a t i v e i n t e n s i ti e s o f t h e t w o p e a k s i n t h e 4 2 -
4 8* 20 r a n g e d e p e n d s t r o n g l y o n t h e s m e c t i t e - e t h y l e n e
g l y c o l c o m p l e x t h i c k n e s s . T h e e x p e r i m e n t a l m a t e r i a l s ,
i d e n t i f ie d a c c o r d i n g t o F i g u r e 2 , f i t t h e t h e o r e t i c a l m o d -
e l ( F i g u r e 4 , s a m p l e s 1 5 a n d 1 6 ).
T h e i m p r o v e d i d e n t if i c a ti o n t e c h n i q u e p r e s e n t e d i n
t h i s s e c ti o n a l l o w s f o r t h e p r e c i s e m e a s u r e m e n t o f t h e
c o m p o n e n t l a y e r r a t i o , t h e t y p e o f i n t e r s tr a t i fi c a t i o n ,
a n d t h e t h i c k n e s s o f s m e c t i t e - e t h y l e n e g ly c o l c o m p l e x
i n o r d e r e d i l l i t e / sm e c t i t e s . I n t e r m s o f t h e c o m p o n e n t
l a y e r s r a t i o a l o n e , t h e d i f f e r e n c e s i n r e s u l t s b e t w e e n t h e
o l d e r ( S ro d o f i, 1 9 8 0 ) a n d t h e n e w t e c h n i q u e a r e n e g -
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I I II I l l ll l I I I I I I I I I I I I I L I I I I I I I I I I I I I I I I I I I I
N O
35
BB2
No ZB ~ ~
N o / d I
I l l l l l l l l l [ l l l l l l ( ) l l l l l l l l l l l l l l l l t l l l I l l l ( l l j
10 ~0 ~0 a0 50 2e
Figur e 8 . Exam ples of X - r ay pow der d i ff ac t ion pa t te r ns of
pur e i l l i te and i l l i t ic ma te r ia l s l ack ing nonco inc ident i l l i t e /
smec t i t e re f lec t ions. Sample numb er s r e f e r to Ta ble 1 . The
ident i f i ca t ion based on BB1, BB2, and I r pa r am ete r s i s g iven
f or each sample . For samples 28 and 41 , a i r - dr y pa t te r ns a re
add ed to the pa t te r ns of the g lycola ted pr epar a t ions to show
001 a nd 003 p eak in tens i t ie s , appl ied in the iden t i f i ca t ion
pr ocedur e as an I r pa r amete r . Sam ple 28 exempl i f ie s a poo r ly
or ien ted pr epar a t ion w her e the 34- 36*20 r eg ion cannot be
explo i ted due to the pr esence of a 20 r e f lec tion .
p e a k l i es b e t w e e n t h e t w o i l l i t e / s m e c t i t e p e a k s b e i n g
m e a s u r e d . I f a s a m p l e i s m o n o m i n e r a l i c i l li t e /s m e c t it e ,
t h e p r e c i s e v a l u e o f p e r c e n t s m e c t i t e m e a s u r e d i n F i g -
u r e 2 s h o u l d f i t w i t h i n t h e r a n g e o b t a i n e d f r o m F i g u r e
7 . I f a s a m p l e i s a m i x t u r e o f i U i t e / s m e c t i t e a n d i l l it e ,
t h e p e r c e n t a g e o f S f r o m F i g u r e 2 s h o u l d b e l o w e r t h a n
t h e r a n g e g i v e n b y F i g u r e 7 . T h e r e a l v a l u e i s t h e o n e
o b t a i n e d f r o m F i g u r e 7. T h e o t h e r o n e i s b i a s e d d u e
t o t h e i n t e r f e r e n c e o f i l l it e 0 0 2 a n d 0 0 3 p e a k s .
E x a m p l e 1 : S a m p l e 2 2 f ro m T a b l e 1 a n d F i g u r e 7 .
Reflections: 17.52" , 26 .79" , 33 .85*20.
B B 1 = 4 .9 * a n d B B = 5 .2 * s u g g e s t p r e v a i l i n g I S t y p e
o f o r d e r i n g . F r o m F i g u r e 2 : 8 % S ; f r o m F i g u r e
7 : 2 6 _+ 4 % S .
Conclusion:
a m i x t u r e o f i l li t e a n d I S - o r d e r e d i l -
l i t e / s m e c t i t e o f a b o u t 2 6 % s m e c t i t e l a y e rs .
E x a m p l e 2 : S a m p l e 1 2 f r o m T a b l e 1 .
Reflections: 16.92" , 26 .75" , 33 .86*20.
B B 1 = 5 . 0* a n d B B 2 = 4 . 8 ~ s u g g e s t I S o r d e r i n g .
F r o m F i g u r e 2 : 2 8 % S ; f r o m F i g u r e 7 ; 2 6 -- -4 %
S .
Conclusion: p u r e i l l i t e / s m e c t i t e c o n t a i n i n g 2 8 % S .
I U i t e / sm e c t i t e m a y b e d i s t i n g u i s h e d f r o m a m i x t u r e
r ic h i n t hi s m i n e r a l b y c o m p a r i n g t h e X R D p a t t e rn s
o f g l y c o l a t e d d i f f e r e n t g r a i n - s i z e f r a c t io n s , e . g ., < 0 . 2
g m a n d 0 . 2 - 0 . 5 g i n . I l li t e i s al w a y s m o r e c o a r s e - g ra i n e d
t h a n i l l i te / s m e c t i t e a n d w i l l t e n d t o a c c u m u l a t e i n
c o a r s e r fr a c ti o n s . S i z e s e p a r a t i o n m a k e s t h e X R D p a t -
t e r n o f th e c o a r s e r f r a c t io n l o o k " m o r e i l l i ti c " o r r e s u l ts
i n a s e p a r a t i o n o f i l li t ic p e a k s . O n t h e o t h e r h a n d , i n
t h e a u t h o r ' s e x p e r i e n c e , p u r e i l l i t e / s m e c t i t e s d o n o t
s h o w s i g n if i ca n t d i f fe r e n ce s in t h e c o m p o n e n t l a y e r s
r a t i o i n d i f f e r e n t s i z e f r a c ti o n s .
T h e s a m p l e m a t e r i a l s u s e d f o r t h e c o n s t r u c t i o n o f
F i g u r e 7 c o m e f r o m b e n t o n i t e s o f v a r i o u s a g e s a n d
l o c a t i o n s ( T a b l e 1 ) a n d i s c o n s i d e r e d t o b e r e p r e s e n -
t a t iv e o f d i a g e n e t i c m a t e ri a l s. T h e p r e c i s io n o f t h e d e -
t e r m i n a t i o n o f t h e p e r c e n t a g e o f s m e c t i t e f r o m F i g u r e
7 g r o w s w i t h i n c r e a s i n g i l l i t e c o n t e n t . T h e i d e n t i f i c a -
t i o n o f h y d r o t h e r m a l m a t e r i a l s , in p a r t i c u l a r p a r a g o n -
i t e / b e i d e l l i t e ( K o d a m a , 1 9 6 6) , r e m a i n s a n o p e n p r o b -
l e m . T h e t h i c k n e s s o f t h e c o m p o n e n t l a y e rs o f
h y d r o t h e r m a l m i n e r a l s i s m o r e v a r i a b l e ( F i g u r e 1 ), a n d
t h e v a r i a t i o n o f th e t y p e o f o r d e ri n g v s . e x p a n d a b i l i t y
h a s n o t b e e n i n v e s t i g a t e d sy s t e m a t i c a l l y .
F i g u r e 7 i s u s e f u l i f t h e a m o u n t o f i l l i te / s m e c t i t e i n
a s a m p l e i s s u f fi c i e n t t o g i v e m e a s u r a b l e r e f l e c t i o n a t
3 3 -3 5 * 2 0 a n d i l l i t e /s m e c t i t e h a s a t l e a s t 6 - 7 % s m e c t i t e
l a y e r s (a t a b o u t t h i s v a l u e , t h e r e f l e c t i o n a t 3 3 - 3 5 ~
d i s a p p e a r s ; s e e F i g u r e 3 ) . T h e r e m a i n i n g i l l i t ic m a t e -
d a i s m u s t b e a n a l y z e d d i f f er e n t ly .
I ll i t ic materials lacking discrete
ill i te sme ctite reflections
X R D p a t t e r n s o f i ll i ti c m a t e r i a l s l a c k i n g d i s c r e te i l -
l i t e / s m e c t i t e r e fl e c t io n s r e s e m b l e c l o s e l y t h e p a t t e r n s
o f p u r e i l li t e ( F i g u re 8 ) . O n l y d e t a i l e d a n a l y s i s o f t h e
p o s i t i o n s , s h a p e s , a n d i n t e n s i t i e s o f t h e b a s a l r e f le c -
t i o n s r e v e a l s th e p r e s e n c e o f th e e x p a n d a b l e l a y e r s . T h e
f ir st s t e p i n i d e n t i f i c a t io n c o n s i s t s o f d i s t i n g u i s h i n g b e -
t w e e n a h o m o g e n o u s , h i g h l y i ll i ti c m i x e d - l a y e r m i n e r a l
( < 6 % S ) a n d i Ui te o r a m i x t u r e o f i l l i t e a n d a m i x e d -
l a y e r m i n e r a l . T h i s d i s t i n c t i o n c a n b e m a d e u s i n g
F i g u r e 2 . I f t h e e x p e r i m e n t a l p o i n t f i ts in t o t h e i l l i te /
s m e c t i t e f i el d , t h e s a m p l e i s a h i g h l y i l l i ti c m i x e d - l a y e r
m i n e r a l , a n d t h e p e r c e n t a g e o f s m e c t i t e c a n b e m e a -
s u re d . T h e c o m p u t e r s i m u l a t i o n h a s s h o w n t h a t e v e n
a t t h e l e v e l o f 2 % t h e p o s i t i o n s o f t h e a n a l y t i c a l r e -
f l e ct i o n s a r e m e a s u r a b l y d i f fe r e n t f ro m t h o s e o f p u r e
i ll it e . A m o n o m i n e r a l i c s a m p l e o f t h i s k i n d m u s t h a v e
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346 St*doff
lays and lay Minerals
BBI and BB2 parameter s smal ler than 4*20 (ISII or-
dering), as established from the analysis of the relation
between the type of ordering and the expandability
(Figure 5). A sampl e of such material was not avai lable
to the author.
If the projection point in Figure 2 lies in the illite
field, the sam ple is pure illite or a mixtur e of this min -
eral with an ordered iUite/smectite. From studies of
artificial mixtures, the most sensitive parameter for
detecting trace amou nts o f the expandable material is
Ir, the ratio of intensi ty ratios of 001 an d 003 reflections
from the same preparation, recorded in the air-dry and
the glycolated state (Table 1). If Ir = 1.0, the mate rial
is 100% nonex panda ble (samples 40 and 41, Table
1 and Figur e 8). If Ir > 1.0, an admi xtu re of expan d-
able material is evident. When Ir parameter is used,
the pre parations mu st be sufficiently thick to absorb
X-rays completely.
Another useful criterion for detecting mino r amo unts
of illite/smec tite is the shifting of 001 and 002 reflec-
tions after glycolation in the opposite directions, iden-
tically to the beh avior of samples identified in the pre-
viou s section (Table 1). Usi ng BB 1 and BB2 paramete rs
admixtu res of IS or ISII-ordered illite/smectite (Figure
8) can be distinguished. It is equivalent, as shown above ,
to the approximate estimation of whether or not the
expandable material has mo re or less than 15% S. The
methods used do not allow for more precise identifi-
cation of such materials. Although the Ir parameter
depends strongly on the layers ratio of illite/smectite
(Table 1), it also depends on the proportion of illite
and illite/smectite in a mixture. It should be note d that
the distinc tion based on Ir between illite and a mixtur e
contain ing a small amo unt o f an ordered illite/smectite
can be made only ifsmectite or rando mly interstratifled
illite/smectite are absent from the sample. I f one of
them is present, it will influence the intensities of 001
and 002 illite in bo th air-dry and glycolated samples.
In surface or shallow buried sediments, the coexistence
of 10-/~ and 17-/~ material is common, e.g., the shal-
lowest sample in Figure 9. In such samples the iden-
tification of 10-A material cannot be carried beyond
stating that it is illitic material lacking discrete illite/
smectite reflections.
APPLICATION OF THE OUTLINED
METHODS IN DIAGENETIC STUDIES
In applying the developed techniq ues to a diagenetic
sequence, several pertinent points should be empha-
sized:
1. Appearance of an expanding compon ent: Ir > 1,
displacemen t of 001 reflection after glycolation toward
higher angles;
2. At about 6-7% expanding compone nt in illite/
smectite: appearance of the reflection at about 35*20
(CuKa radiation).
I I I I I I I I I I I I I I I I I I I I f I I I ~ I I I I I I I I ~ l q q q - l q q q - F l
% " ~ ' I S l l
I I I I I l f l l l J l I l l i l l J I I I J [ I i l l i i [ i l [ [ [ l l I I I l i
IO 2o 30 ~o 5o 2e
Figure 9. Representative X-ray powder diffraction patterns
ofglycolated 4~
4. Trans ition from IS to rando m interstratification
at abo ut 4 0-50% S: inflection or a small reflection at
~5~ and a diffuse ba nd at 32-33~
Beginning at 6% S, measur ement s of expan dability are
possible in mixtures with illite, providing the illite/
smectite is sufficiently abu nda nt to give a measurable
reflection at 33-35*20.
The most complete example of the illite/smectite
evoluti on with depth k nown to the author is shown in
Figure 9. The samples are shales from the Wrzegnia
IG-1 well in central Poland. The deepest samples are
from Ca rboni ferou s rocks at ~ 5500 m below the sur-
face, with a temperature of ~200~ and a vitrinite
reflectance near 3.0. The XRD patterns show that
mixed-layer illite/smectite is present in all samples but
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Vol . 32 , No. 5 , 1984 X-ray pow der d i f f rac t ion ident i f ica t ion of i l l i te 349
Re s i ime e - -D ie 1 0 -/~ To n k o m p o n c n te n y o n s e d ime n ta re n G e s t e in e n ( IU i t e ) s i n d g e w b h n l i c h Misc h u n -
gen aus 100% nicht expan die rb arem I l l i t und e i nem rcge lm~ll3igcn I l l i t /Smekt i t -W cchse l lagerun gsminera l .
We n n d a s V c rh ~ il t ni s y o n I l l i t /Sme k t i t i n e in e r Misc h u n g a u s re i c h t , u m c in c h me l3 b a rc n Re fl e x z w i sc h e n
3 3 u n d 3 5* 20 (Cu K a -S t ra h lu n g ) z u e rz e u g c n , d c r n i c h t m i t e in e m I l li t re f le x z u sa mme n i 'a l l t , d a n n k a n n
d a s V e rh ~ tn i s d e r K o mp o n e n te n sc h ic h t e n u n d d i e A r t d e r We c h se l l a g e ru n g f t i r d a s We c h se l l a g e ru n g s-
min e ra l b e s t im mt w e rd e n . D ie Id e n t i f i k at io n s t e c h n ik , d ie i n d i e se r U n te r su c h u n g e n tw ic k el t w u rd e, b e ru h t
a u f d e n fo lg e n de n e x p e r ime n te U e n Erg e b n i sse n fo r g e o rd n e te I l l i t /Sme k t i t -We c h se l l ag e ru n g e n d i a~e n e -
t ischen Ursp rungs: (1) Die D icke der IUi t lagen in den IUi t /Smekt i t -W echse l lagerungen bet r~gt 9 ,97 A; (2)
d ie Dicke des Smekt i t -Ath ylenglyk olkom plexes re icht yon 16 ,7-16 ,9 A; (3) I l l i t -Smekt i twechse l lagerungen
bi lden e ine kont inuie r l iche Abfolge yon Wechse l lagerungstypen--unrege lm~iBige , unrege lmaBige /IS, IS ,
IS / IS II , IS I I - -u n d j e d e r Ty p g e h 6 r t z u e in e m b e s t imm te n Be re i c h y o n Ex p a n d ie rb a rk e i t.
D ie n e u e U n te r su c h u n g s me th o d e b a u t d i e Co m p u te r s im u la t io n sm e th o d e a u s, d ie y o n R. C . Re y n o ld s
u n d J . H o w e r e n tw ic k e lt w u rd e , u m so l c h e se d ime n ta re n Ma te r i a l i e n m i t e in z usc h li e l3 e n , b e i d e n e n
diskre te r IUi t vorherrscht , d ie wenig I l l i t /Smekt i t en tha l ten , und d ie , a ls so lche , f r f iher nur durch e inen
Illi t-IC..ristalliniffttsindex bes chr ieb en wur den. [U.W .]
R t s u m 6 - L c s c o m p o s t s a r g il e d e 1 0 A de r o ch e s s t d im e n t a i r e s ( i l li t es ) s o n t c o m m u n t m e n t d e s m t l a n g e s
d ' i l l it e 1 0 0 % n o n e x p a n s ib l e e t d 'u n m in t r a l o rd o n n 6 a c o u c h e s me la n g tc s i l l i t e/ sme c t it e . Si l a p ro p o r t i o n
d ' i l l i t e / sme c t i t e d a n s u n me la n g e e s t su i t isa n t e p o u r p ro d u i re u n e r t f l e c t i o n me su ra b le e n t r e 3 3 -3 5 ~
( ra d i a t i o n Cu K a ) q u i n e c o in c id e p a s a v e c u n e r t f l e c t i o n i l l i t e , o n p e u t d t t e rmin e r l a p ro p o r t i o n d e
c o u c h e s d u c o mp o s t e t l e g e n re d ' i n t e r s t r a t i fi c a t i o n d u m in t ra l a c o u c h e s mt l a n g te s . La t e c h n iq u e d ' i d e n -
t i f ic a t i o n d tv e l o p p t c d a n s c e t t e 6 ru d e e s t b a s t e su r l e s t ro u v a il l e s e x p 6 r ime n tal e s su iv a n te s p o u r d e s i l l i te /
smect i tes d 'or ig in e d iagtn t t iqu e : (1) l ' tpa is seur de la couche f l l i te dans les i l l i te /smect i tes est 9 ,97/~: (2)
l ' tpa i sseu r du complexe g lycol smec t i te - t thyl~ ne s ' t ten d de 16 ,7 a 16 ,9 A; (3) les i l l i te /smect i tes formen t
u n e s6 q u e n c e e o n t in u e ll e d e t y p e s d ' i n t e r s t r a t i f i c a t i o n - -a u h a sa rd , a u h a sa rd IS , IS , IS / IS I I, IS I I - - e t
c h a q u e ty p e e s t a p p a re n t6 a u n e 6 t e n d u e sp t c i f iq u e d e p o u v o i r d e d i l a t a t i o n .
La n o u v e l l e t e c h n iq u e 6 1a rg it l a m t th o d e d e s imu la t io n a l ' o rd in a t e u r d tv e lo p p tc p a r R . C . R e y n o ld s
e t J . H o w e r p o u r i n c lu re le s ma t t r i a u x s td ime n ta i r e s q u i so n t d o min 6 e s p a r l a p r t se n c e d ' iU it e d i sc r t t e ,
o n t u n b a s c o n te n u e n iU i te / sme ct i te , e t, e n t a n t q u e t el s , n 'o n t j u sq u 'a p r t se n t 6 t6 d t c r i t s q u e p a r u n
inde xe de c r is ta l lin i t6 d ' i l l i te . [D.J .]
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