corrensite mineralogical ambiguities and geologic significance

5/20/2018 CORRENSITE Mineralogical Ambiguities and Geologic Significance

1/54

UNITED STATES DEPARTMENT OF THE INTERIOR

GEOLOGICAL SURVEY

CORRENSITE: Mineralogical Ambiguities

and

Geologic Significance

By

Phoebe

L . Hauff

Open-File

Report 81-850

1 9 8 1

T h i s report

i s

preliminary a n d has n o t been

edited o r

reviewed

f o r conformity

with

U . S .

Geological Survey

standards.


2/54

TABLE OF

CONTENTS

Page

A b s t r ac t . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . 1

I nt ro d uct ion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . 2

History

o f

t h e Study o f Corrensite......................................

2

Definition

o f

Corrensit e .. . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . .. . .

3

Physical

and

Chemical Criteria f o r t h e Identification o f Corrensite..... 5

X-ray

Diffraction

Analysis Criteria................................ 5

Differential Thermal Analysis

Criteria............................. 1 4

Chemical Criteria.................................................. 1 6

Scanning Electron Microscopy Criteria............... ............ ...

2 0

Swelling Layer

Characteristics.......................................... 2 2

Summary o f

Mineralogical

Data

Implications..............................

2 5

Geologic

Significance o f Corrensite Occurrences............... .......... 2 5

Distribution o f Corrensite Occurrences Through Geologic

Time.......

2 6

Hypothesized

Origins o f

Sedimentary Corrensite

Species............. 2 8

Occurrences

o f

Corrensite i n Sedimentary Environments..............

3 2

E v a p o r i t e - B e a r i n g

H o s t

R o c k s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

32

Carbonate-Bearing Host Rocks..................................

3 2

Transitional Marine Environments............ ......... ........ . 3 2

Occurrence o f Corrensite i n t h e

Supai

Group Rocks.................. 3 2

Summary o f Sedimentary Occurrences................................. 3 6

Occurrence o f Corrensite i n Hydrothermal and Low-grade

Metamorphic

R ocks . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . 3 7

Summary

and Discussion..................................................

3 7

R ef erences . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . 4 1


3/54

LIST OF FIGURES

Page

Figure 1 .

X-ray diffraction

patterns o f

various corrensite

samples.....

6

2 . Differential

thermal analysis

curves

from a corrensite

s am ple. . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 7

3 . Ternary diagrams showing elemental relationships from s o m e

corrensite

samples

documented

i n t h e

literature............

1 9

4 . Scanning

electron microscope

photographs

and

energy

dispersive spectra o f corrensite specimens................. 2 1

5 . A diagrammatic

representation

o f an

intact

chlorite

structure which h a s been breached o r not completed......... 2 3

6 . Distribution

o f

corrensite and associated magnesium-bearing

minerals

through

geologic time.............................

2 7

7 . Diagrammatic representation

o f

t h e hypothesized origins

o f

authigenic, sedimentary corrensites.................... .

2 9

8 . Stability f i e l d s f o r authigenic corrensites and

associated minerals........................................ 3 1

LIST

OF TABLES

Page

Table I . T h e reactions

o f

various corrensite species

t o

standard

clay analyses

t e s t s

a s

shown

b y t h e superorder

angstrom

positions derived b y X-ray powder diffraction methods....... 4

I I . Tabulation

o f

X-ray diffraction data

from

patterns

o f

corrensite species

shown

i n F i g u r e 1........................

7

I I I .

X-ray

diffraction

data

f o r corrensite

species

from t h e

literature which cite vermiculite

a s

swelling-layer

cons t it u ent . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . 9

I V .

X-ray diffraction

data

f o r

corrensite

species

from

t h e

literature t h a t

c i t e

swelling chlorite a s swelling

layer

constituent.......................................... 1 1

V .

X-ray diffraction

data f o r corrensite

species from

t h e

literature t h a t

cite

montmorillonite a s t h e swelling

layer constituent..........................................

1 2

V I .

X-ray diffraction data f o r corrensite species from t h e

literature

t h a t

c i t e

saponite a s t h e swelling

layer

cons tit u ent . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . 1 3

V I I . Compilation

o f DTA

data f o r corrensite-like phases

from

literature

s ou rces . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . 1 5

V I I I . Chemical analyses

o f

s o m e corrensite

samples

from t h e

lit erat u re. . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . 1 8

I X .

Corrensite

occurrences i n

evaporite-bearing rocks

X . Corrensite occurrences i n primarily carbonate-bearing

rocks . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . 3 4

X I . Corrensite occurrences i n transitional

marine o r

near-marine environments.................................... 3 5

X I I . Hydrothermal

corrensite

occurrences...........................

3 8

X I I I . Low-grade metamorphic corrensite occurrences..................

3 9

i i


4/54

ABSTRACT

This

paper

i s a

summary

of

the information available on the mixed-layer

clay

mineral

corrensite.

For 30

years

corrensite

and

corrensite-like

phases

have been reported

in

the literature.

The

best-known occurrences are

in

the

German

and

English

Keuper

Marl, the German Zechstein, the

French

Jura Basin,

and the

Texas-New

Mexico Delaware Basin. Corrensite

i s

d efined

a s a

1 : 1 ,

regularly, interstratified , probably

trioctahedral

c l a y mineral species

composed

o f a 14A

chlorite and

a swelling-clay layer. The

latter

has

been

variously

d efined

a s a

v ermlculite, a

montmorillonite,

a

saponite, and a

swelling

chlorite. The most

common constituent

o f

the

swelling

layer appears

t o be a

smectite w i t h swelling chlorite

the

next most

common.

Vermiculite

does not seem t o

be a

v alid species name

for

the swelling

layer.

Differential

Thermal

Analysis curves show

endothermic

peaks

at

100-200C, 550-660C, and

8 30-8 5 0C

w i t h

an

exothermic

peak

at

850-900C.

The eleven

chemical

analyses

for corrensite, taken

from

the literature, can be

separated

on

an

environmental

and chemical

basis; hy drothermal

samples

lie in

the

vermiculite

field; sedimentary samples

cluster

into the

saponite

field.

Corrensite

i s

found in three ty pes

o f

en v ironm ent s ed im ent ar y ,

hyd rothermal, and low -grade

metamorphic. I t has

a

d efinite

distribution

through geologic

time

w i t h the

major sedimentary occurrences being

in the

Paleozoic

and

early Mesozoic

while

the

hy drothermal

occurrences

are

grouped

in the

Cretaceous

and Tertiary.

Sedimentary

corrensite i s hy pothesized t o

form

by

ion aggradation

o f

a

less-ordered

species. Sedimentary corrensites are shown t o exist

in

evaporite-bearing rocks, in carbonate-bearing host rocks, and in

transitional

marine

lithologies.

I n general, t h e shallow

marine conditions

o f a warm,

e p i c o n t i n e n t a l

sea

seem

t o favor corrensite formation.


5/54

INTRODUCTION

T h i s article

i s a survey o f t h e

corrensite d i l e m m a t h e unfortunate

assignment

o f

t h e mineral name corrensite

t o

a t least four discrete

mixed-layer clay s p e c i e s ; chlorite-vermiculite, chlorite-montmorillonite,

chlorite-swelling chlorite, a n d

chlorite-saponite. I t i s t h e author's

intent

t o present a summary o f t h e ambiguities

a n d

contradictions encountered i n t h e

literature under

t h e heading

o f corrensite

o r

corrensite-like p h a s e s .

There

i s

considerable

reference

material available on

corrensite.

Unfortunately, many researchers have been confronted with t h e

problems

o f

duplicitous definitions a n d much

o f

t h e subsequent work

h a s

been poorly

defined

tending

t o compound

t h e confusion.

I t i s

n o t

t h e objective o f t h e author t o offer any definite solutions

at

t h i s

t i m e .

Additional

research,

compilations

a n d

data integration must b e

carried o u t o n representative samples a n d an extensive research

project t o

t h i s e n d

i s being

implemented. H o w e v e r ,

i t i s t h e

intent

o f

t h i s work

t o

summarize

t h e

available information

i n a s

useful detail

a s

i s

practical,

outline

specifically

t h e existing

problem a r e a s ,

offer

s o m e

guidelines

f o r

phase identification,

a n d

discuss why t h e dilemma

exists.

A s many literature citations a s possible

a r e

included i n t h i s p a p e r .

H o w e v e r , some references

have

been excluded. T h e criteria used f o r exclusion

were duplications, incomp lete d a t a , a n d lack o f t i m e

t o

translate o r t o

abstract.

I t

w a s not

t h e

intention

t o

slight any

researcher.

T h e author

would appreciate t h a t oversights b e brought

t o

her attention s o t h a t

subsequent work can b e a s complete a s

possible.

HISTORY OF THE

STUDY

OF CORRENSITE

Corrensite h a s appeared in t h e literature a s a recognized species

f o r

nearly thirty y e a r s .

A

mixed-layer

phase

with what

w a s later

defined a s

corrensite characteristics w a s synthesized b y

Calliere

and Henin

in 1 9 4 9 . A s

a naturally occurring species i t w a s f i r s t documented from t h e Triassic Keuper

Marl in England b y I . Stephen

and

D . M . C .

MacEwan

in

1 9 5 0

and 1 9 5 1 . Honeyborne

( 1 9 5 1 )

also

reported i t from t h i s

locality. T w o excellent a n d more

detailed

characterizations o f corrensite from t h e Keuper i n England were

done

i n Davis

( 1 9 6 7 ) and MacNeill ( 1 9 7 8 ) .

The term corrensite was first used b y Friedrich

Lippmann

in

h i s

1 9 5 4

paper on

t h e

G e r m a n , Triassic,

Keuper

M a r l .

T h e

mineral was

named i n honor o f

Professor

C .

W .

Correns

o f

Gottingen, Germany.

D r .

Lippmann,

i n h i s o w n

research

( 1 9 5 4 , 1 9 5 6 , 1 9 7 6 )

a n d i n t h a t

o f

h i s

various

countrymen

(Lippmann

and S a v a s c i n , 1 9 6 9 ; E c h l e ,

1 9 6 1 ;

B e c h e r , 1 9 6 5 ; Schlenker,

1 9 7 1 ) ,

presented

detailed examinations

o f

corrensite

occurrences

in

t h e

primarily evaporite

sequences

o f

t h e Keuper a n d associated

formations.

Corrensite

was

reported from another evaporite deposit, t h e famous

Permian

Zechstein

o f

Germany b y Dreizler

( 1 9 6 2 )

a n d Braitsch

( 1 9 6 0 , 1 9 7 1 ) .

I t

was found

in

t h e

evaporite-bearing Permian S a l a d o Formation

o f

t h e Delaware

B a s i n , o f New Mexico b y Grim

a n d h i s

co-authors ( 1 9 6 0 ) with additional

work

done b y

Fournier ( 1 9 6 1 ) ,

Madsen ( 1 9 7 8 ,

personal communication),

Bodine

( 1 9 7 8 )

and

Loehr ( 1 9 7 9 ) .

2


6/54

Another

famous

basin occurrence f o r corrensite i s t h a t

o f

t h e Jura i n

F r a n c e . Here corrensite

was

documented b y Millot

and his

associates ( 1 9 6 3 ) ;

by Martin

Vivaldi and MacEwan ( 1 9 5 7 ) ,

Lucas a n d Ataman

( 1 9 6 8 ) , b y

Lucas

( 1 9 6 2 ) ;

a n d

T a r d y ,

e t

a l . ( 1 9 7 2 ) .

There are also numerous

reports

o f t h i s

mineral

from hydrothermal

environments.

J a p a n , i n

particular, hosts

many

corrensites

a n d

corrensite-

like minerals formed

a s

byproducts

o f

o r e deposition. Corrensite species have

been

identified from

widespread geographic localities: South West A f r i c a ,

I c e l a n d , J a p a n ,

Mozambique,

I t a l y ,

I n d i a ,

Austria, R u s s i a ,

S p a i n ,

S c o t l a n d ,

and

i n t h e United S t a t e s , N e v a d a , North C a r o l i n a , C o l o r a d o , Tennessee, Kansas,

California,

I l l i n o i s , and

Arizona; and from diverse geologic enviro nments

such

a s

pegmatites,

geothermal s y s t e m s , ore-rock

alteration

z o n e s , dike-intruded

s h a l e s , hydrothermally altered calcareous argillites, altered basalts, various

low-grade

metamorphic

alteration r e g i m e n s , transitional marine and near-shore

marine environments,

and

shallow marine carbonates. Most o f

these

occurrences

have been summarized i n t a b l e s which appear later i n t h i s p a p e r .

T h i s

brief

historical summary

o f

documented corrensite occurrences

indicates t h a t t h e mineral

has

been recognized b y , relatively

s p e a k i n g ,

a

great

number o f workers i n

t h e l a s t

thirty

y e a r s .

DEFINITION OF CORRENSITE

The

most confusing

aspect o f t h e

corrensite problem

i s

i n

t h e

definition

o f corrensite. I n

g e n e r a l ,

t h e literature i s

i n

agreement

t h a t

corrensite

i s

a

1 : 1 , r e g u l a r , interstratified, probably trioctahedral, species composed

o f a chlorite layer

and

a

swelling-clay l a y e r . Disputation a r i s e s , however,

when attempts a r e made t o characterize t h e swelling-clay l a y e r .

Corrensite

h a s

been documented

a s

regularly interlayered:

chlorite-swelling c h l o r i t e ,

chlorite-saponite,

chlorite-montmorillonite, a n d

chlorite-ven niculite. These different

species do

seem surficially t o conform

t o t h e definitions given

by their authors. The

lattice

s p a c i n g s ,

i n

angstroms, shown i n Table

1 , attempt t o define

numerically

t h e components

o f

t h e various

mixed-layer

s p e c i e s . T h i s i s a generalized v e r s i o n ,

a s

variations

on

these spacings seem

t h e

rule

rather

than

t h e exception. T h e swelling-

chlorite

variety

expands with g l y c o l , b u t

d o e s

n o t collapse with h e a t .

The

montmorillonite

layer

both expands

with glycol a n d contracts with h e a t , a s

does

t h e

s a p o n i t e ,

although t h e saponite ma y expand more with glycol

than d o e s

t h e montmorillonite. T h e vermiculite constituent d o e s n o t expand with glycol

b u t d o e s

collapse with h e a t .

Each

o f t h e s e ,

t h e r e f o r e , s e e m s

t o b e a distinct

definable

p h a s e .

T o simplify nomenclature, throughout

t h i s

paper

t h e

t e r m s smectite,

montmorillonite, vermiculite,

a n d

swelling-chlorite will b e

used

without

t h e

chlorite modifier

t o

mean

t h e nonchlorite layers

o f a

corrensite

s p e c i e s . Unless otherwise n o t e d , t h e species designations used are those

assigned b y t h e original authors. Although corrensite

i s

defined a s

possessing a

1 : 1

relationship between i t s l a y e r s , t h i s

i s

seldom

t r u e , a s

will

be shown

through t h e

compilations i n t h e

section

on

X-ray

diffraction

d a t a .

There are

usually minor

discrepancies,

and

many t i m e s ,

major o n e s .


7/54

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8/54

From

t h e numerical values f o r t h e layer components listed i n Table

I ,

i t

becomes apparent t h a t t h e

C

axis

dimension

can

vary with

species

t y p e . T h e

assumption

i s

made t h a t t h e chlorite component

remains

a constant

1 4 A .

The

variation

i s

then

attributed t o t h e interlayer

space

between t h e t w o

components and/or t h e octahedral

layer

o f t h e

swelling-clay component.

These

variations and their potential causes will b e discussed after s o m e

o f

t h e

physical

and

chemical information

f o r

corrensite

h a s

been

presented.

D r . Lippmann

o f

t h e University o f Tubingen i n Germany prefers t h a t t h e

controversial layer b e

referred

t o

a s

a swelling clay layer without a

species name

(personal communication, 1 9 7 9 ) . H e i s currently researching t h e

thermodynamic properties

o f

corrensite

from

t h e Keuper Marl i n Germany

t o

define t h e

mineral

more precisely

( L i p p m a n n ,

1 9 7 7 a , b ; 1 9 7 9 ) .

PHYSICAL AND CHEMICAL CRITERIA FOR THE IDENTIFICATION

OF

CORRENSITE

An examination o f

t h e

various physical and chemical criteria used t o

identify

t h i s

mineral will

b e

helpful toward an understanding

o f

i t .

T h e

following sections assess t h e literature data and present research performed

b y t h e author and assistants using X-ray diffraction, differenti al thermal

analyses,

scanning

electron

microscopy,

a n d chemical

analyses o f various

corrensite

s p e c i e s . Unfortunately there

i s

very

little

cross-referencing

o f

samples

between t h e

different

t y p e s

o f analyses

compiled

from t h e

literature. However, interesting

t r e n d s

d o appear

a n d

some new perspectives

on

corrensite

can b e

g a i n e d .

X-Ray Diffraction Analysis

Criteria

The most commonly used method f o r t h e identification

o f

corrensite i s

X-ray diffraction.

A

comprehensive

study

b y t h e

author

o f

powder-diffraction

data presented i n t h e literature a s identification

criteria, h o w e v e r , s h o w s

t h a t

t h e

values given are anything b u t

consistent.

Considering t h e

inconsistent nature

o f

t h e mineral under discussion, t h i s inconsistency i s n o t

surprising.

Selected X-ray powder

diffraction

patterns o f

corrensite samples given

t o

t h e author b y other researchers

a r e

shown i n Figure 1

A n

attempt

h a s been

made

t o

present

cross

section

o f

types

and

environments f o r t h e r e a d e r s '

comparison. T h e corresponding numerical

data

from these patterns are

tabulated

i n

Table I I .

T h e

patterns were

run on

t h e less-than-2 micron

f r a c t i o n ;

carbonates,

sulphates, a n d other silicates were removed by routine

processes

( J a c k s o n , 1 9 7 4 ) .

The sample i n Figure 1 A i s

from

t h e

P e r m i a n ,

evaporite-bearing Salado

Formation o f

New

Mexico. I t

i s

termed chlorite-vermiculite by Madsen

(personal communication, 1 9 7 9 ) .

T h e

mid-Tertiary

evaporite

layers o f

nonmarine r e d

beds

from t h e California S e s p e Formation ( F l e m a l , 1 9 7 0 ) yielded

t h e chlorite-montmorillonite

o f

Figure

I B . Sample 1 C

comes also

from an

evaporite deposit, t h e

famous

Triassic Keuper

Marl

o f

Germany

( L i p p m a n n ,

1 9 5 4 ,

1 9 5 6 , 1 9 7 6 ) .

The swelling-layers have been

called

swelling-chlorite,

vermiculite

and

montmorillonite. T h e chlorite-montmorillonite o f t h e

Pennsylvanian a n d

Permian

Supai Group

o f

t h e Grand C a n y o n , Arizona i s shown i n

Figure I D ( M c K e e , e d . ,

in p r e s s ) .

T h i s i s a transitional,

marginal marine

5


9/54

Figure 1 . X - r a y

diffraction

patterns o f various corrensite

s a m p l e s .

Machine

parameters

w e r e :

Copper

K-alpha radiation

scanned

a t o n e degree

2-theta

per m i n u t e ;

t w o degrees 2-theta

p e r inch

(samples D

and

F were

r u n

a t

four degrees 2-theta per i n c h ) ;

counts

p e r second varied with t h e

s a m p l e s .

A . Chlorite-vermiculite from t h e Salado Formation, New Mexico.

B .

Chlorite-montmorillonite from

t h e

Sespe Formation, California.

C . Chlorite-swelling chlorite from t h e

Keuper

M a r l , Germany.

D . Chlorite-montmorillonite from t h e S u p a i G r o u p , Arizona.

E . Chlorite-swelling chlorite from t h e Crescent Formation,

Washington.

F . Chlorite-saponite from t h e Elena

F o r m a t i o n ,

Nevada


10/54

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11/54

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12/54

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13/54

environment.

The chlorite-swelling chlorite

o f

Figure I E

i s

a low-grade

metamorphic

variety o f corrensite from t h e Eocene

Crescent

Formation o f t h e

Olympic Peninsula, Washington ( P e v e a r , written communication, 1 9 7 9 ) .

T h i s

corrensite occurs i n volcaniclastic lenses o f a

s e a floor

basalt u n i t .

Figure

I F illustrates t h e pattern o f a chlorite-saponite variety from t h e

hydrothermally altered argillites o f t h e Devonian

a n d

Mississippian Eleana

Formation i n Nye

C o u n t y ,

Nevada.

Six X-ray patterns provide insufficient data f o r more

than

j u s t a

discussion o f their identification. I f t h e criteria shown i n Table I are

applied t o t h e superorders tabulated

i n

Table I I , t h e

first

conclusion i s

t h a t

very

few o f

these samples conform exactly

t o t h e

criteria. S a m p l e s B , C ,

D ,

a n d

F give

fairly good f i t s a n d probably can

b e

classified, from

t h e

X-ray

d a t a , a s smectites (montmorillonites, saponites).

S a m p l e

C

a n d

especially

sample F show greater swelling characteristics than d o samples B a n d D . This

swelling might indicate t h a t

they are saponites. H o w e v e r , sample

A ,

which

swells significantly (32A=14A+18A), a n d collapses insignificantly

( 2 8 A = * 1 4 A + 1 4 A ) , does not

exhibit

t h e acceptable criteria f o r

a

vermiculite

( t h a t

i s

nonswelling and collapse t o a 24A=14A+10A p h a s e ) . This nonconformity

also applies

t o

sample

E .

I t

collapses more

than

A ,

b u t n o t a s

low

a s t h e

vermiculite required 1 0

angstroms. Subsequently,

sample

A

and more certainly

sample E are

probably

o f t h e swelling-chlorite

variety. O n e problem

with

t h e identification

o f

t h e s e phases

i s t h a t ,

d u e

t o

degree

o f

crystallinity and

instrument limitations, superorders

cannot

always

b e

resolved adequately.

Unfortunately, t h e superorder positions

are

t h e

r e a l

key t o t h e identification

o f

t h e s e different s p e c i e s .

I t appears t h a t ,

based on

t h e X-ray diffraction d a t a , t h e species t y p e s

could

b e reduced

from four

t o t w o

(smectite and

swelling

chlorite). T h e

literature data compiled f o r t h i s study

a n d

other data presented i n t h i s

paper

suggest

such

a t r e n d .

An examination o f literature data b y species

i s

in order h e r e .

A

clarification o f X-ray identification criteria

may

n o t b e possible from t h i s ,

b u t a t l e a s t

a

better understanding

o f t h e source o f t h e

confusion should

emerge. T h e majority o f t h e vermiculite

species

o f corrensites reported i n

t h e literature swell where they should n o t and/or d o n o t collapse e n o u g h .

A

compilation

o f

these

data i s given

in Table

I I I . S o m e references have

been

omitted because either n o data from X-ray analysis were reported o r they were

inconclusive; even s o m e

o f

t h e d a t a

included

are many times insufficient f o r a

valid identification. When considering t h i s compilation, please recall t h e

criteria shown i n Table I ,

i . e . :

a phase ( u n t r e a t e d , 28A=14A+14A) t h a t d o e s

n o t swell with glycolation (glycol = 2 8 A ) b u t collapses with heat

t o

24A

( 1 4 A + 1 0 A ) i s probably

a

vermiculite. Certain interpretive latitudes must b e

allowed b u t 3 0 and 3 1 angstroms i s very generous f o r t h e untreated values.

H o w e v e r ,

other

variables

such a s t h e

retention

o f

additional

interlayer waters

due

t o high

humidity

conditions

can also

affect

these

superorder

spacings.

T h e presence o f interlayer aluminum hydroxyl complexes

could also

influence

t h e

reactions o f t h e clay structure t o glycol

and

h e a t .

A l l

t h e

s a m p l e s ,

presented

i n

t h i s t a b l e , except o n e ,

s w e l l

t o varying

d e g r e e s ,

which

vermiculites should n o t

d o . O f

t h e 1 2 samples i n t h e t a b l e , 6

collapse t o

24A

o r

l e s s

a s

those

with

vermiculite

( o r

smectite) layers s h o u l d ,

and a t l e a s t

4

collapse

with

heat

t o values

greater t h e n

2 4 A , indicating

t h a t

t h e swelling

layers

might b e

more validly

considered t o

b e

swelling

chlorites.

8


14/54

x

.*

4 f J

^f>

^


15/54

Table III. X-ra y diffraction d a t a f o r corrensite

s p e c i e s

from

t h e

literature

which cite vermiculite a s

t h e

swelling

l a y e r

constituent

[ N u m e r i c a l

Reference

B r a d l e y and Weaver

1 9 5 6

Alietti

1 9 5 8

Grim

e t

a l .

1 9 6 0

F o u r n i e r

1 9 6 1

Peterson

1 9 6 1

Johnson

1 9 6 4

Becher

1 9 6 5

Gradusov

1 9 6 9

R a o a n d Bhattacharya

1 9 7 3

K o p p

a n d

F a l l i s

1 9 7 4

Lippmann

1 9 5 6

values

a r e

Untreated

2 9 . 2

1 4 . 7

9 . 7

7 . 3

2 9 . 0

30.0

1 4 . 4 8

3 0 . 5

1 4 . 2 6

2 9 . 4

1 4 . 7

1 0 . 0

7 . 4

2 8 . 5

2 8 . 5

1 4 . 2

7 . 0 8

2 9 . 0

1 4 . 3

3 0 . 9

1 4 . 9

7 . 2

1 3 . 8

9 . 0

7 . 1

2 9 . 0

1 4 . 5

7 . 2

4 . 7 9

given

i n

a n g s t r o m s ]

Glycol

3 1 . 0

1 5 . 5

1 0 . 2

7 . 7

3 1 . 0

1 5 . 4 9

3 1 . 5

1 5 . 5

3 1 . 2

1 5 . 6

1 0 . 0

7 . 8

2 8 . 5

3 2 - 3 3

1 6 . 2

1 4 . 2

8 . 1

3 1 . 9

3 1 . 5

1 5 . 2

7 . 2

1 5 . 8

7 . 9

7 . 1

3 1 . 0

1 5 . 5

7 . 7 5

5 . 1 5

550C

( 2 4 ) ?

1 2

8

6

29.0

1 2 . 0

n o t

given

2 1 . 5 5

1 3 . 8 1 ( c

1 2 . 0

1 0 . 0

8 . 0

2 4

27.7-28

1 3 . 9

2 3 . 6 5

13.7

1 2 . 1

8 . 0

7 . 1 ( c h

13.0


16/54

There i s only

one

sample

in the

table

that

ad heres

t o the

vermiculite

p a r a m e t e r s t h a t o f

Johnson

(1964).

Therefore, what emerges from

the

perusal

o f

Table

I I I , i s that

perhaps

the

term

vermiculite applied

t o

t h e

swelling layer

o f a

corrensite

species

identified

by

X-ray diffraction techniques i s not necessarily

a

v alid

usage.

This

conclusion assumes

acceptance o f the

premise

that

v ermiculites

d o

not

swell. Some o f these samples

( Bradley

and Weaver, 1 9 5 6 ; Fournier, 1 9 6 1 ;

Peterson, 1 9 6 1 ; Gradusov, 1 9 6 9 ;

Kopp

and Fallis, 1 9 7 4 ) might be

reclassified

as

falling

closer

t o

the

smectite variety

w hereas

the samples o f

Alietti

(1958), Becher

(1965), Rao

and Bhattacharya

( 1 9 7 3 ) ,

and

Lippmann ( 1 9 5 6 )

seem

t o act more a s a swelling-chlorite

v ariety.

I f one

next examines various swelling-chlorite samples

a s

presented

in

the

literature and compiled here

in

Table

I V , they

seem

t o

hold slightly

more

true t o their definition of

28A

(untreated)

swelling

t o 3 1 A (14A+17A) w i t h

g l y c o l

and collapsing t o

28A

(14A+14A) w i t h heat. O f the

nine data

sets i n

Table I V , four are

fairly close

t o the 28A

untreated

value; nearly all swell

greater

than the theoretical value

o f

31A and

a l l ,

except the

two

o f

Kimbara

and

Sudo (1973) in

w h i c h

the

swelling layer behaves more like

a smectite,

collapse

t o 26-28A.

The

literature values

for t h e montmorillonite-cited species o f corrensite

are tabulated

in

Table V .

These samples

s h o w the

best fit

t o

the

established

criteria

w i t h few digressions. The

same

applies t o

the

saponite

variety

samples listed

in

Table V I .

I f one calculates the distribution and percentages

o f

all the v alues

given

for the samples in Tables

I I I ,

I V , V ,

and VI

on

an

unweighted ,

v olume

basis,

the v alues having

the

higher percentages a r e :

untreated

glycol

2 9A

30A

3 1 A

3 2A

3 1 .

5A

3 3 A

2 4A

2 8A

38 .5% o f

20 .5%

2 9%

2 3 . 7 %

1 6 %

1 6 %

43%

1 6 %

5 5 0C

Choosing

the

highest from each group

yields:

untreated

= 29A (14A +

1 5 A )

glycol

= 31A (14A + 1 7 A )

550C

=

24A

(14A

+

1 0 A )

10


17/54

Table

IV. X -r a y diffraction

data

for corrensite s p e c i e s

from

t h e literature

t h a t

c i t e

swelling-chlorite a s s w e l l i n g l a y e r constituent

[ N u m e r i c a l

values a r e given in a n g s t r o m s ]

Reference

Honeyborne

1 9 5 1

Lippmann

1 9 5 4

Martin

Vivaldi

a n d

MacEwan

1 9 5 7

Martin Vivaldi

a n d

MacEwan

1 9 6 0

Heckrodt a n d Roering

1 9 6 5

Rimbara

and

S u d o

1 9 7 3

MacNeill

1 9 7 8

Pevear

1 9 7 9

Personal communication

Untreated

1 4 . 5

2 8 . 3

1 4 . 2

3 0 . 0

1 4 . 7

3 0 . 0

2 8

3 0 . 0

1 4 . 4

3 1 . 5

1 4 . 9 7

3 0 . 2

1 4 . 7 7

2 8 . 5

1 4 . 3

7 . 0 5

2 8 . 0

1 4 . 2

8 . 8 8

Glycol

1 6 . 4

3 2 . 3 3

1 6 . 2

3 5 . 0

1 6 . 8

3 2 . 7

3 1

3 1 . 0

1 5 . 0

3 2 . 9

1 5 . 7 1

3 2 . 5

1 5 . 4 4

3 - 2 . 7 2

1 5 . 5

7 . 8

3 2 . 0

1 5 . 2

8 . 0

550C

1 3 . 8

2 8 . 0

( 1 4 )

1 3 . 1

28.5

1 3 . 6

8 . 8

2 8

1 3 . 6 4

2 2 . 6

1 2 . 1

2 3 . 9

1 1 . 9

2 7 . 6 1

1 3 . 8

6 . 8 6

2 3 - 2 6

1 3 . 2

1 1


18/54

Table V . X - r a y diffraction data

for

corrensite

species

from the literature

t h a t cite montnorillonite a s t h e swelling layer

constituent

[Numerical

values

Reference

Earley and Milne

1 9 5 6

Earley

e t

a l .

1956

Sudo and Kodama

1 9 5 7

Sudo

1 9 5 9

Lucas

1962

W y art

and

Sabatier

1 9 6 7

Flemal

1970

Wilson and Bain

1 9 7 0

Schlenker

1 9 7 1

Tomasson and

Rris

tmanns o

ttir

1 9 7 2

Blatter

e t a l .

1973

Savatzki

1 9 7 5

Almon e t

a l *

1 9 7 6

McKee,

e d .

( i n

press)

are given

Untreated

29.0

29.0

1 4 . 1

30.0

15.0

9.96

7.52

29.8

28.5

1 4 . 2

9 . 5

7 . 1

29.1

28.5

13.65

7 .14

29.0

13.9-14

29.0

1 4 . 6

14-14.6

29.0

14-15

28-29.5

14-14.5

2 9

14.48

7.23

2 9

1 4 . 5

7 . 2

in angstroms]

Glycol

31.7

32.0

31.8

1 5 . 5

32.3

30.5

1 5 . 2

9 . 9

8 . 8

30.9

33.0

15.55

7 . 8 1

32.0

15-15.1

31.5

1 5 . 5

15.3-15.8

31.0

1 7

1 4

30-31.5

15.2-15.5

3 1

15.2 3

7 . 6 2

31+

1 5 . 5

7 .7 5

550C

23.3

24.0

12.0

24.0

11.9

11.7

2 4

1 2

8 . 0

2 3 . 7

13.7

28.5

1 3 . 2

2 4

1 2 . 4

2 3.5

1 2 . 1

12-14

12-12.9

23-24

1 2

2 4

11.8-12.2

23.8

11.9

7.9

2 4

1 2


19/54

Table V I . X - r a y diffraction data for corrensite species from the literature

that cite

saponite

a s

the swelling

layer constituent

[Numerical

values

are

given

i n angstroms]

Reference

Alietti

1 9 5 8

Kimbara

1 9 7 3

Kimbara and

Sudo

1 9 7 3

Blackmon

1979

Personal

communication

Loehr

1 9 7 9

Untreated

29.4

30.4

14.72

9.82

7 . 3 1

30.0

15.8

9 . 8

7 . 4

29.4

1 4 . 7

29.0

13.7

9 . 6

Glycol

3 1 . 6 - .

7

31.5

1 5 . 4 9

32.7

32.6

16.35

8.33

32.0

1 5 . 4

550C

23.5

11.8

8.75

23.9

11.94

23.0

24.5

1 2 . 2

( 2 4 . 9 ) ?

12.45

13


20/54

This does n o t necessarily support

a

conclusion toward corrensite

being

primarily a smectite-type species

b u t d o e s

indicate t h a t t h e majority o f t h e

samples researched t o date seem t o have smectite-like characteristics. I t

would also seem less confusing

t o refer t o

t h i s species a s having smectite

rather

then

montmorillonite o r saponite l a y e r s , a t

least

until more

specific identification criteria are developed, o r chemical analyses

a r e

available.

The

swelling-chlorite variety a s opposed t o vermiculite appears t o b e t h e

other common s p e c i e s . T h i s hypothesis

i s

supported b y t h e t r e n d shown in

Table I I

a n d

Figure 1 and will b e given further credence with data presented

i n

later sections.

Differential Thermal Analysis Criteria

Differential

thermal

analysis

( D T A )

i s another useful technique f o r

characterizing clay minerals. Unfortunately,

n o t

a

great deal

o f work

h a s

been done on

t h e corrensite

s p e c i e s .

I n MacKenzie's book

o n

DTA

curves f o r

clays

( 1 9 5 7 ) ,

Caillere

a n d

Henin present

a

helpful summary

on

DTA

curves

f o r

corrensite and related t y p e s .

A s

would b e anticipated, there

i s

a distinctive

suite

o f

peaks t h a t

can b e used

effectively

t o

characterize s o m e

o f t h e

components o f corrensite p h a s e s .

O n e

specific reaction

range

i s a direct

manifestation

o f t h e

brucite l a y e r ,

which may

b e most useful structurally

toward identifying

corrensite.

There i s

first

a

lower

temperature endothermic peak between 1 0 0

O -200C,

closer

t o 1 5 0 C ,

which indicates l o s s o f absorbed w a t e r . T h e hydroxyls o f t h e

brucite

layer a r e l o s t

between 550C t o a little more

than 6 0 0 C , and

sometimes a s

high a s 6 6 0 C . T h e

structure

still maintains integrity, however,

until

t h e mica

layer

i s

also dehydrated, around

830-850C.

T h e exothermic

peak

o f

recrystallization also

falls

very close

h e r e ,

between 850C

t o

near

9 0 0 C .

Table VII i s a

compilation

o f

s o m e

o f t h e

published

DTA

c u r v e s . Most

o f

t h e s e

values

are estimates from t h e published

diagrams.

They generally

conform t o t h e criteria postulated

b y

Caillere

and

Henin ( i n

Mackenzie,

1 9 5 7 ) . H o w e v e r , there a r e n o apparent species correlations. Until

t h e

more

definite parameters o f chemical

composition,

X-ray diffraction data

a n d

interlayer configurations can b e established, t h e s e temperature

values can

only serve

a s guidelines

f o r

future investigations.

T h e

DTA

curves i n Figure 2 are from Bradley

a n d

Weaver ( 1 9 5 6 ) .

They

were

chosen

t o

b e

included here because

they

n o t

only

illustrate

t h e

corrensite

species

under

discussion, b u t also

i t s hypothesized constituent p a r t s . T h e

bottom curve

i s indicative o f

t h e s e represented b y numerical

values

i n

Table

V I I . T h e X-ray data

in Table

I I I f o r t h e Bradley

a n d

Weaver sample

has

smectite characteristics. Because corrensite i s defined a s a trioctahedral

s p e c i e s , t h o s e

samples

designated dioctahedral

have

been

labeled

questionably

corrensite.

14


21/54

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(

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(

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(

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(

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(

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(

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(

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(

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8

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0

(

8

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5

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0

,

9

1

5

(

8

9

0

)

(

9

0

0

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(

9

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0

)

(

9

5

0

)

(

8

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0

)

(

8

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0

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(

8

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0

)

R

e

f

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c

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A

l

l

e

t

t

l

,

1

9

5

8

A

l

l

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t

t

l

,

1

9

5

8

G

r

i

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a

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o

h

n

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,

1

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3

H

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c

k

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d

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R

o

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r

l

n

g

,

1

9

6

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e

y

s

t

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,

1

9

5

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H

e

y

s

t

e

k

,

1

9

5

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u

d

o

a

n

d

K

o

d

a

m

a

,

1

9

5

7

K

l

a

g

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s

a

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d

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h

i

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,

1

9

5

7

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l

p

p

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a

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,

1

9

5

4

,

1

9

5

6

P

e

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s

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,

1

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1

B

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v

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1

9

5

6


22/54

Chemical

Criteria

There a r e only a few chemical analyses f o r corrensite t y p e minerals i n

t h e literature. T h i s i s understandable when t h e difficulty i n obtaining a

pure representative separate i s considered. Table VIII i s

a

compilation o f

t h e s e

chemical analyses. I t

w a s n o t

always clear from t h e

t e x t

what

w a s

being

analyzed,

a clay separate o r t h e whole

r o c k ;

or how refined t h e analytical

sample w a s .

The

elemental percentages

were

calculated

from

these

data

and projected

onto t h e ternary diagrams shown i n Figure 3 .

Approximate fields f o r

montmorillonite,

s a p o n i t e ,

vermiculite,

a n d

magnesium-bearing chlorites

have

been plotted on Figure 3 A . T h e Mg-bearing

chlorite field i s

included

f o r comparison

because

there w a s insufficient

chemical

analyses

t o

plot a swelling-chlorite f i e l d . T h e

chemical data

were

taken

from

analyses reported

i n

D e e r , H o w i e ,

a n d

Zussman ( v o l . 3 , 1 9 6 2 ) ,

Grim

( 1 9 6 8 ) , Weaver and Pollard ( 1 9 7 3 ) , Starkey and Blackmon ( 1 9 7 9 ) .

The

effect o f t h e chlorite constituent

h a s n o t been considered a n d

t h e

chlorite most likely varies i n composition

among

t h e s a m p l e s , although i t i s

probably magnesium-bearing.

I f

t h e chlorite layer

can be

characterized

with

any

confidence, and

i t s influence

subtracted,

a

s h i f t

t o t h e

l e f t

would

b e

postulated.

Until

there a r e more corrensite

chemical

data generally available,

i t i s

rather

pointless t o speculate t o o f a r

o n

t h e

distribution

shown

i n

Figure 3 .

H o w e v e r , s o m e

inferences can b e

drawn

from

these diagrams.

I n general

there

i s credible separation between

samples

from hydrothermal environments

and

those

from sedimentary environments except f o r

sample

5

(which

was identified

a s

coming

from

a

sedimentary environment).

T h e

term

hydrothermal

i s

an

author designated o n e .

There

were n o chemical data reported f o r low-grade

metamorphic corrensite

occurrences.

Another very interesting observation i s

t h e scattered pattern

o f

t h e various s p e c i e s . Using t h e a u t h o r s '

designations,

there i s only s o m e consistency

t o

species distribution. T h i s

could

suggest

t h a t there are perhaps fewer discrete

phases

than previously

identified.

I t i s interesting t o note t h a t t h e majority o f t h e

hydrothermal

corrensites f a l l i n t o t h e vermiculite

field

even though

only

t w o

o f

them ( n o .

8 and

n o .

9 )

have

been

identified

a s having vermiculite

layers

while

n o . 6 , a

sedimentary chlorite-vermiculite, plots o n

t h e fringe

o f t h a t f i e l d . T h e

saponite

variety

o f

n o .

2

falls

definitely

i n t o t h e

vermiculite

f i e l d .

N o .

4 ,

identified a s a chlorite-saponite,

seems by

t h i s criteria t o b e o n e .

However,

neither

o f t h e

montmorillonite species ( n o . 5

and n o .

7 ) a r e close

t o

t h e

montmorillonite f i e l d .

16


23/54

Figure 2 Differen tial Thermal

Analysis

Curves from

a

corrensite s a m p l e .

These show a corrensite

o f

t h e vermiculite

variety

and

i t s

constituent

p a r t s .

Reproduced from Bradley and Weaver ( 1 9 5 6 , p .

5 0 2 )

with t h e

permission

o f t h e

authors.

VERMICUUTE

C H LOR ITE

CORRENSITE

100 C 300 C

800

C

900C

7


24/54

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25/54

Figure 3 T e r n a r y diagrams showing elemental relationships from some

corrensite

samples

documented i n t h e

literature. A .

S i - A l - M g ; B . S i -

( A l + F e

( t o t a l ) )

- M g ;

C . Si-Al-

( F e + M g ) ; D . Si-Al-(Fe +

M g ) .

Numbers on t h e

plots refer

t o t h e following

references:

1 . S h i m o d a , in

Sudo and S h i m o d a ,

1 9 7 8 (swelling

c h l o r i t e ) ;

2 .

Alietti,

1 9 5 8

( s a p o n i t e ) ;

3 . Kimbara e t

a l . ,

i n S u d o

a n d

S h i m o da , 1 9 7 8 ( s a p o n i t e ) ; 4 .

Takahashi,

1 9 5 9 ( s a p o n i t e ) ; 5 .

Almon

e t a l . ,

1 9 7 6 (montmorillonite);

6 . Peterson,

1 9 6 1 ,

1 9 6 2 (vermiculite); 7 . Earley

e t

a l . , 1 9 5 6 (montmorillonite); 8 .

S u g i u r a ,

1 9 6 2

(vermiculite); 9 . A l i e t t i ,

1 9 5 8

(vermiculite);

1 0 .

Bradley

and W e a v e r ,

1 9 5 6

(vermiculite);

1 1 . B o d i n e , 1 9 7 8

( s a p o n i t e ) . T h e

species given

in parentheses

a r e

t h e

a u t h o r s ' designation f o r t h e

swelling layer constituent;

circles

refer t o sedimentary occurrences,

squares t o hydrothermal occurrences.

1 9


26/54

g

e

A

+

A

5

S

M

A

A


27/54

Table

VIII

also provides s o m e additional generalizations. T h e corrensite

samples found i n t h e sedimentary environment have a higher silica content.

T h e hydrothermally

produced

corrensites have both higher

magnesium

and

aluminum

contents

than their

sedimentary counterparts.

F o r

t h e most p a r t , t h e

range

within t h e magnesium

percentage f o r hydrothermal corrensites i s small

( a b o u t

3 %

from 23%-26+%), whereas there

i s a greater latitude

f o r

t h e A l

content w i th a

7.6%

r a n g e . I n

a hydrothermal environment

where

M g

i s a

less-common element b u t restrictions o n

A l

a r e n o t

a s

stringent, t h i s

relationship

i s

n o t surprising. T h e

reverse

trend

appears

in

t h e

sedimentary

environments where there i s a wide range

o f

magnesium content (nearly

1 2 % )

b u t

a restricted range f o r A l ( 4 . 4 % ) .

I t

might

b e

generalized t h a t

i t

t a k e s l e s s aluminum a n d l e s s magnesium

t o

make a sedimentary

corrensite; however,

sedimentary

samples have

more silica

then

t h e

hydrothermal

varieties.

T h i s might

suggest

different basic

mechanisms

o f

formation o r a t least different

precursors.

Iron

i s t h e confusing chemical

v a r i a b l e .

Theoretically, i f i t i s i n t h e

structure i t s e l f , t h e

iron

potentially substitutes

i n t o

t h e cation positions

o f t h e octahedral l a y e r . I n Figure 3 B ,

t h e

plot o f S i , M g , ( A l +

F e

tota i ) ,

h a s a distribution relative t o t h e other figures toward t h e A l +

F e

e n d ,

which

would seem

t o indicate

t h a t t h e i r o n

i s a t

least i n p a r t

substituting

i n t o t h e

A l

positions. Both iron and aluminum

may

also substitute i n t o t h e magnesium,

positions. This

was substantiated

b y

a

p l o t

o f

Mg-Fe-Si, which

i s

n o t shown

h e r e . T h e

separation o f t h e

sample p o i n t s

shown

i n

t h e Si-Al-(Fe + M g )

p l o t

i n Figure 3 C could

imply

t h a t t h e iron i s within t h e structure because a

division between hydrothermal

and

sedimentary

samples

i s evident. T h i s i s i n

contrast t o Figure 3 D ,

t h e

Si-Al-(Fe

+ M g ) p l o t , where

t h e clustering

i n d i c a t e s , b u t still with environmental segregation, t h a t t h e iron i s more

likely external t o t h e

s t r u c t u r e ,

potentially

an oxide

coating

o r

impurities

i n t h e s a m p l e .

T o

s u m m a r i z e ,

t h e

chemical

data suggest

t h a t depositional environment i s

an important consideration

toward t h e

determination

o f

species

t y p e .

Scanning

Electron

Microscopy

Criteria

Few

s c a n n i n g ,

electron microscope

( S E M )

photographs o f corrensite phases

have been published because

they a r e

difficult t o

o b t a i n . S a m p l e

crystallinity

i s

usually

p o o r ;

grain s i z e i s

s m a l l ; mixed-layer

configurations

a r e

notorious

f o r poorly

defined morphology;

and

corrensites,

especially from

sedimentary environments, appear t o b e s o fragile t h a t concentration processes

t e n d

t o

alter

their

morphological characteristics.

T h e

best

SEM pictur e

published t o

date

o f

corrensite i s t h a t o f A l m o n ,

e t

a l . ( 1 9 7 6 ) .

T h i s

portrays a chlorite-montmorillonite variety found i n a transitional marine

environment

o f

calcareous sandstones.

T h e

corrensite

w a s

found here a s pore

a n d vein f i l l i n g s , t h u s making

i t easier t o

visually

locate

a n d also

giving

i t

s o m e p r o t e c t i o n .

Figure 4 contains photographs

o f t w o previously unpublished

corrensites

with

accompanying energy dispersive system ( E D A X ) s p e c t r a . I n

figure 4 A , t h e corrensite i s t h e darker

band

o f near-vertical

grains

through

t h e center o f

t h e p i c t u r e .

Figure 4 B i s

an enlargement

o f t h e

lower right

corner

o f

Figure 4 A . T h i s sample

i s t h e

low-grade

metamorphic

chlorite-

swelling

chlorite from Washington. T h e curled

edges are probably an

artifact

o f

t h e electron b e a m .

T h e

configuration

shown

i n these

t w o

pictures i s

2 0


28/54

Figure

4 . S c a n n i n g

electron microscope photographs

and

energy dispersive

spectra o f corrensite

specimens.

A .

Chlorite-swelling chlorite from Washington

magnification

2 , 4 0 0 X .

B . Chlorite-swelling chlorite from Washington

magnification

6 , 6 0 0 X ; t h i s i s an enlargement

o f A .

C .

Chlorite-saponite from Nevada

magnification -

10,200X.

D . Energy dispersive spectra

f o r

A

a n d

B .

E .

Energy dispersive

spectra

f o r

C .

21


29/54

similar

t o

the cornflake habit described

by Almon,

e t a l .

(1976).

Figure 4D

i s t h e corresponding energy dispersive

spectra

for t h e Washington

corrensite. The first three peaks shown are M g , A l , S i , respectively, and

most probably relate

t o

the corrensite. Figure

4 C

represents

the

h y d r o t h e r m a l

chlorite-saponite

from Nevada. EDAX spect ra

o f this

saponite

i s

shown

in

Figure

4 E

and also shows

M g , A l , S i a s

the major elemental constituents.

This

habit

i s

similar

t o a

smectite.

These pictures are included here t o illustrate

one more

p o t e n t i a l method

that

can

be

used t o

c h a r a c t e r i z e

corrensite. Until

numerous

samples

o f

corrensite

are

studied w i t h the S E M ,

no

v alid conclusions relative

t o

habit

can

be

drawn.

SWELLING

LAYER CHARACTERISTICS

An explanation for the

behavior

o f

the swelling layer o f

t h e

corrensite

species was proposed

by

Martin Vivaldi and MacEwan

(1960).

These researchers

h y p o t h e s i z e d

that t h e

brucite layer w i t h i n the

swelling-layer

component

o f t h e

mixed-layer

species was gapped having lost

magnesium

and hyd roxyl ions

resulting

in

an island

or

pillar configuration. Twenty

years

later

this

explanation seems less

sophisticated

than

required

t o explain the

b e h a v i o r a l

idiosyncracies

o f this

complex mineral.

Utilizing a

simplified

projection of t h e

basic structure

o f a

14A-chlorite,

shown

in part A o f

Figure

5 ,

and

that same

chlorite w i t h

a

gapped brucite

layer (Figure 5 B ) , s

corrensite mineralogical ambiguities and geologic significance

Documents

occurrence o f corrensite

p o r i t e b e

stability f i e

r i n gh o s tr o c

t h i s reporti spreliminary

n t h esupaigroup rocks

definitiono fcorrensit

n hydrothermal