x ray in illite

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


4/13

3 4 0 S ro d o f i


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


5/13

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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Vol. 32, No. 5, 1984 X-ray pow der dif f ract ion identif ica t ion of i l l i te 343

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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Vol. 32, No. 5, 1984 X-ra y pow der dif f ract ion identif icat io n of i l l i te 345

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


10/13

346 St*doff


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


11/13


12/13


13/13

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 .]

x ray in illite

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