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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.
5/20/2018 CORRENSITE Mineralogical Ambiguities and Geologic Significance
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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
5/20/2018 CORRENSITE Mineralogical Ambiguities and Geologic Significance
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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
5/20/2018 CORRENSITE Mineralogical Ambiguities and Geologic Significance
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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.
5/20/2018 CORRENSITE Mineralogical Ambiguities and Geologic Significance
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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
5/20/2018 CORRENSITE Mineralogical Ambiguities and Geologic Significance
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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 .
5/20/2018 CORRENSITE Mineralogical Ambiguities and Geologic Significance
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T
a
b
l
e
I
.
T
h
e
r
e
a
c
t
i
o
n
s
o
f
v
a
r
i
o
u
s
c
o
r
r
e
n
s
i
t
e
s
p
e
c
i
e
s
t
o
s
t
a
n
d
a
r
d
c
l
a
y
a
n
a
l
y
s
e
s
t
e
s
t
s
s
h
o
w
n
b
y
t
h
e
s
u
p
e
r
o
r
d
e
r
a
n
g
s
t
r
o
m
p
o
s
i
t
i
o
n
s
d
e
r
i
v
e
d
b
y
X
-
r
a
y
p
o
w
e
r
d
i
f
f
r
a
c
t
i
o
n
m
e
t
h
o
d
s
,
S
p
a
c
i
n
g
s
g
i
v
e
n
i
n
t
h
e
l
a
s
t
c
o
l
u
m
n
a
p
p
l
y
t
o
v
a
l
u
e
s
o
f
t
h
e
c
o
l
l
a
p
s
e
d
s
t
r
u
c
t
u
r
e
a
f
t
e
r
h
e
a
t
i
n
g
t
o
5
5
0
C
.
L
A
C
P
O
S
C
N
C
R
T
S
E
C
O
R
T
S
W
E
N
C
O
T
C
O
R
T
M
O
N
M
O
R
L
O
N
T
C
O
R
T
S
O
N
T
C
O
R
T
V
M
I
C
T
U
R
2
A
2
A
2
A
2
A
E
H
E
G
L
Y
L
3
A
3
A
3
A
2
A
5
C
S
N
S
2
A
1
1
2
A
2
1
+
1
0
2
0
A
+
1
0
A
2
1
A
10
5/20/2018 CORRENSITE Mineralogical Ambiguities and Geologic Significance
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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
5/20/2018 CORRENSITE Mineralogical Ambiguities and Geologic Significance
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
5/20/2018 CORRENSITE Mineralogical Ambiguities and Geologic Significance
10/54
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5/20/2018 CORRENSITE Mineralogical Ambiguities and Geologic Significance
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5/20/2018 CORRENSITE Mineralogical Ambiguities and Geologic Significance
12/54
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5/20/2018 CORRENSITE Mineralogical Ambiguities and Geologic Significance
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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
5/20/2018 CORRENSITE Mineralogical Ambiguities and Geologic Significance
14/54
x
.*
4 f J
^f>
^
5/20/2018 CORRENSITE Mineralogical Ambiguities and Geologic Significance
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
5/20/2018 CORRENSITE Mineralogical Ambiguities and Geologic Significance
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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
5/20/2018 CORRENSITE Mineralogical Ambiguities and Geologic Significance
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
5/20/2018 CORRENSITE Mineralogical Ambiguities and Geologic Significance
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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
5/20/2018 CORRENSITE Mineralogical Ambiguities and Geologic Significance
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
5/20/2018 CORRENSITE Mineralogical Ambiguities and Geologic Significance
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
5/20/2018 CORRENSITE Mineralogical Ambiguities and Geologic Significance
21/54
T
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1
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2
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1
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2
1
0
6
6
0
C
6
5
5
(
5
5
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+
)
5
5
5
(
5
8
0
)
(
5
8
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)
(
6
1
0
)
5
1
0
(
6
1
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)
(
6
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5
5
0
8
3
0
C
8
3
0
(
8
5
0
)
8
5
0
(
8
5
0
)
(
8
5
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)
(
8
7
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8
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)
(
8
3
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(
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x
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p
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9
5
6
5/20/2018 CORRENSITE Mineralogical Ambiguities and Geologic Significance
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
5/20/2018 CORRENSITE Mineralogical Ambiguities and Geologic Significance
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
5/20/2018 CORRENSITE Mineralogical Ambiguities and Geologic Significance
24/54
T
a
b
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V
I
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e
5/20/2018 CORRENSITE Mineralogical Ambiguities and Geologic Significance
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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
5/20/2018 CORRENSITE Mineralogical Ambiguities and Geologic Significance
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g
e
A
+
A
5
S
M
A
A
5/20/2018 CORRENSITE Mineralogical Ambiguities and Geologic Significance
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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
5/20/2018 CORRENSITE Mineralogical Ambiguities and Geologic Significance
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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
5/20/2018 CORRENSITE Mineralogical Ambiguities and Geologic Significance
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