Feldspar Mineralogy [2 ed.] 0939950146

Table of contents :
Page 1
Titles
REVIEWS In
(Formerly: "Short Course Notes")
Volume 2
SECOND EDITION
FELDSPAR MINERALOGY
The Authors
MINERALOGICAL SOCIETY OF AMERICA
REV002copyright.pdf
Page 1
Tables
Table 1
Page 1
Titles
FELDSPAR MINERALOGY
FOREWORD TO THE SECOND EDITION
iii
REV002ACKN.pdf
Page 1
Titles
ACKNOWLEDGMENTS
SELECTED REFERENCE WORKS
Page 1
Titles
FELDSPAR MINERALOGY
TABLE of CONTENTS
CHAPTER 1.
P.H. RIBBE
The CHEMISTRY, STRUCTURE and NOMENCLATURE of FELDSPARS
CHAPTER 2.
ALUMINUM-SILICON ORDER in FELDSPARS:
DOMAIN TEXTURES and DIFFRACTION PATTERNS
P.H. RIBBE
Page 2
Titles
The preeession method 32
The oseillation method 32
Peristerites
Bytownite
High plagioelases
'e '-plagioelase
CHAPTER 3.
H. KROLL & P.H. RIBBE
LATTICE PARAMETERS, COMPOSITION and Al,Si ORDER in ALKALI FELDSPARS
vi
Page 3
Titles
CHAPTER 4.
LATTICE PARAMETERS and DETERMINATIVE METHODS
CHAPTER 5.
D.B. STEWART & P.H. RIBBE
Tables
Table 1
Page 4
Titles
CHAPTER 6.
R.A. YUND & J. TULLIS
SUB SOLIDUS PHASE RELATIONS in the ALKALI FELDSPARS
CHAPTER 7.
R.A. YUND
MICROSTRUCTURE, KINETICS and MECHANISMS of ALKALI FELDSPAR EXSOLUTION
Page 5
Titles
CHAPTER 8.
DIFFUSION in FELDSPARS
R.A. YUND
CHAPTER 9.
PHASE EQUILIBRIA of PLAGIOCLASE
Tables
Table 1
Page 6
Titles
CHAPTER 10. P.H. RIBBE
EXSOLUTION TEXTURES in TERNARY and PLAGIOCLASE FELDSPARS;
CHAPTER 11.
A.M. HOFMEISTER & G.R. ROSSMAN
CHAPTER 12.
SOME CHEMICAL PROPERTIES of FELDSPARS
Tables
Table 1
Page 7
Titles
CHAPTER 12, continued
CHAPTER 13.
DEFORMATION of FELDSPARS
J. TULLIS
Page 8
Titles
CHAPTER 13, continued
APPENDIX: INDEXING FELDSPAR POWDER PATTERNS
Page 1
Titles
Chapter 1
CHEMISTRY, STRUCTURE and NOMENCLATURE of FELDSPARS
Tables
Table 1
Page 2
Titles
tP
i;j
ALKALI
FELDSPARS
Page 3
Titles
Four- membered tetrahedral ring
- .f,zl'a
- ()
Actual
n
Stylized
Page 4
Titles
a
__ 1
Page 5
Titles
Ie Id spar
gismondine
[lTOI
[110J
5
Tables
Table 1
Page 6
Page 7
Page 8
Titles
T
1
c'
block - - four -fold
\. ~~' (e) Feldspar building
)
//1/'
+ // (b) Two views of crankshaft linkage of four-membered rings
Page 9
Tables
Table 1
Page 10
Page 11
Titles
T2mc
Page 12
Page 13
Titles
C2Im
o
Sonidine
T,
z
I
~/
13
Tables
Table 1
Page 14
Page 15
Titles
o.
c.
pi
Page 16
Titles
PI
Page 17
Tables
Table 1
Page 18
Tables
Table 1
Page 19
Titles
I - anorthite
Page 20
Page 1
Page 2
Page 3
Titles
HIGH I
j SANIDINE
LOW
Mean T -0 distance, A
~
Approximate AI content of T site
I
.:
I
Tim
DI TlmcC; "e,C:
I / I
(i) MONOCLINIC HOST
(ii)
(iii)
(iv)
(v)
ttO = t1m = t.oc = time
Page 4
Page 5
Titles
20 h .
25
Tables
Table 1
Page 6
Page 7
Tables
Table 1
Page 8
Page 9
Titles
c
900
p
i1
Ii [At/IAt-Si)l
29
Page 10
REV002C002_p31-55.pdf
Page 1
Page 2
Titles
The precession method.
The oscillation method.
Page 3
Titles
33
Tables
Table 1
Page 4
Titles
• f
e
1--------+----
"c I •
e
c !J
o
21
022
012
002
b* -d
P-anorthite
T - anorthi te
Huttenlocher
'e' - plcq, (An65)
001 O~
,a Q
e
,e
020
Beggild (Ansa)
'e' - plag. (An30)
Peristerite
Albite
S --I __ --
e __ ::: = ::-:3 ----
-----..,__--­
c ----:;mrll I
- --- d
mol % anorthite
--1---
s -
100
*
bl,2
80
60
40
g
20
o
* 0*
01 __ 2====
34
Tables
Table 1
Table 2
Page 5
Tables
Table 1
Page 6
Page 7
Titles
~ ~
Page 8
Titles
c*
~
ffimffmmR
I 1 I
I I 1
o.!o.o.o.lo.o.o.p-; If
. /.0.0.0.1.0.0.0./. ' ..•.
38
Page 9
Titles
b
a
Tables
Table 1
Page 10
Titles
Albite.
40
Page 11
Titles
Peristerites.
Page 12
Page 13
Titles
1,75 rr----,-----,-----,,-----,------,--,-----,----,-----,-----,-,
1,70
a.
o.
'tJ co ....
a. co
I U co
>- U
c: rl
ro m ...... m
rn .. c "C
o rn ~ m
rn a 0 U) 0
U a. r.... to
en ........ k tU
CD r-4 m u
m c:
....
L-' Q)
"
I~
60
Page 5
Titles
'" ~
~u,
"''''
"''''
-
c- -sr \0 -a
r--O r--O
......
oco ca e- 0('-
0\ ro en CO C1\ rn
cc
•
-
u a •• V
65
Page 10
Titles
......
e- n ..... t") Nt")
'"
•
>-
If)..;;t am N.;;;t 000 moo com om Nn LnN D-=:t
....................
"'N
"
. ...
-e
"
. ...
"'N
o
~
"
....
o
"
....
o
....
"
. ...
""
'"
"
~ ~'"
'"
"
....
"'N
"''''
....
'"
"
..,
"''''
'"
"
....
"
"''''
a.
s-:
"
"
....
'"
o
....
"'N
"''''
'"
a.
'"
"
....
'"
"
....
"
~I E
'" "
u,
"
"
~I NO
,
•
..
+ //1
Vo I u me ij.i
.1/
tl.!,
»»
I . "'l"
.-./ "
j'
..
c
E
>
Mol % Or
Page 17
Titles
94.00
93.0·
92.0·1-
a,y
91.0·
\
r
a
-
-
-
90.0·
89.0·
88.0·
r
• • • y
o_o_._'_._._._.. . . .. to _!._._+.
__L_._ I , I , I ·-:-T-~-·,-:-1-~~·LA-L"1
__ L, 1 ' I ,
Ab 20 40 60 80 Or
73
Page 18
Page 19
Titles
Z r
Page 20
Tables
Table 1
Page 21
Page 22
Titles
12.76
o
12.80
12.84
12.88
1292
12.95
13.00
13.04
Tables
Table 1
Table 2
Page 23
Page 24
Titles
*
;..... 90.0°
89.0°
88.0°
AA
86.0°
87.0°
88.0°
89.0°
90.0°
Page 25
Page 26
Page 27
Titles
.,
oL _
~
83
Tables
Table 1
Table 2
Page 28
Tables
Table 1
Page 29
Page 30
Page 31
Titles
7.90.
785
·~78o.
=
.-
='
~775
- .
770.
~~~M':::.:line
• ~.7.9189~03361 t,m
\. tr1To.=785o.8-o..1548 ·t)
Sonidine "e., ~ L
~:, ..... "Irthoctoses"
.~
,
trllo. = 7.8919 -0..2626· t.o
Low ~pop,
765
0.
0..2
0..4
0.6
0.8
1.0.
Page 32
Tables
Table 1
Table 2
Page 33
Page 34
Titles
710
720
90
Tables
Table 1
Table 2
Page 35
Page 36
Titles
Table 6. Equations and coefficients to calculate from tr[110], [110] (10
'-
-- 0.20
0«
,~
,
0.00
0.10
COEFFICIENTS (alkali feldspars)
030
92
Tables
Table 1
Table 2
Page 37
Page 38
Page 39
Titles
- - - -- - -- - - - - - - - - - - - - -- -- - - - ------ - - - -- --- -- - - -- -----
95
Page 40
Page 41
Page 42
Titles
-t ..
.. ,.
Tables
Table 1
Table 2
Page 43
Titles
t-='
-
~
....
E
-z:
o
&
(t,0 - tim); AI from T1m to T10
-~---~-
,
,
,
Page 1
Titles
Chapter 4
LATTICE PARAMETERS and DETERMINATIVE METHODS for
H. Kroll
Page 2
Titles
An
BO
60
An [mol%J
40
20
Ab
912
90.0
892
B96
888
894
90B
90.4
880
An
80
60
An[mol%J
40
20
Ab
116.6
1162 f-~----=-i:: --- k: I
Tables
Table 1
Table 2
Table 3
Page 3
Titles
3D
20.
An [mol'!,l
10.
Ab
60.0.
T ['CI
100.0.
120.0.
80.0.
Page 4
Page 5
Titles
91 -
92 -
93 -
94 -
95-
86
87
88
89
90
91
92
93
94
95
c
~?
• No.Co
1\
b
Page 6
Page 7
Titles
4400.'
4Jo.o.'
9600'
950.0'
9900'
98.00·
970.0.'
960.0'
950.0.'
-+-----j 94.0.0.'
Or
25
50
An [mol%]
75
An
Page 8
Titles
ex
>
e
T[l]
Page 9
Titles
100
1000
800
600
T [OC]
400
zoo
o
b (mel)
S2
'1$
-50
a
0(3 (mel)
- (100)
lo
o·
Page 10
Page 11
Titles
t,o-(t,m)
Tables
Table 1
Table 2
Page 12
Tables
Table 1
Page 13
Page 14
Titles
755
760
755
'1, LoY'
1, An JJ - 50
;j? \ + Or - containing
~ ... \ \ /' An 16.5
'i9..
'"
~..r
c High AnO-J3
750 755 no 775
755
780
775
765 770
trll0 [AJ
760
7.70
765
745
750
~760
0'09
10
/ Low Albite
876 Ab 20 40 60 80 An
88.0
90.4
90.8
912
900
6' [0]
896
Page 1
Titles
Chapter 5
OPTICAL PROPERTIES of FELDSPARS
Page 2
Titles
*
Tables
Table 1
Page 3
Page 4
Titles
0.50
o
jt
I ------ __ b ~~
__ 0----1----- no ------ _j
~
~
[ • • •••••••••••••••••••••••••••••• •• ••••••••• • ·1· ••••••••••••• > u
~.: oHIM
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c," :g
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I A Xf
I o~'I\~«,/ 'rl -Y;{ ~
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I
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c:,"",./"; I
.-

Citation preview

REVIEWS In MINERALOGY (Formerly: "Short Course Notes")

Volume

2

SECOND EDITION

FELDSPAR MINERALOGY P. H. Ribbe,

EDITOR

and

SERIES

EDITOR

The Authors Anne

&

M. Hofmeister

George

R. Rossman

Division of Geology and Planetary Science California Institute of Technology Pasadena, California 91125 v Herbert

Kroll

Institut fur Mineralogie Westfaf ische Wilhelrns- Uni versi ta t 4400 Munster, West Germany Paul

H. Ribbe

Department of Geological Sciences Virginia Polytechnic Institute & State University Blacksburg, Virginia 24061 1/

Joseph

V. Smith

Department of Geophysical Sciences University of Chicago Chicago, Illinois 60637 " David

B. Stewart

United

States Geological Survey 959 National Center Reston, Virginia 22092

" Jan Tullis

&,/ Richard

A. Yund

Department of Geological Sciences Brown University Providence, Rhode Island 029 12

MINERALOGICAL

SOCIETY

OF AMERICA

COPYRIGHT Mineralogical

Society of America

First edition Second edition

1975 1983

PRINTED BY BOOKCRAFTERS, Inc. Chelsea, Michigan 48118

REVIEWS in MINERALOGY (Formerly:

"Short Course Notes") ISSN 0275-0279

Volume 2, Second Edition: FELDSPAR MINERALOGY ISBN 0-939950-14-6 -------------------------------------------------------------------------

Aditional copies of this volume as well as those listed below may be obtained at moderate cost fromThe Mineralogical Society of America 2000 Florida Avenue, NW Washington, D.C. 20009 --------------------------------------------------------------------------

Volume 1 SULFIDE MINERALOGY, P.H. Ribbe, editor

(1974) (1975; revised 1983)

284 p. 360 p.

2

FELDSPAR MINERALOGY, P.H. Ribbe, editor

3

OXIDE MINERALS, Douglas Rumble III, editor

4

MINERALOGY and GEOLOGY of NATURAL ZEOLITES, F.A. Mumption, editor (1977)

232 p.

5

ORTHOSILICATES, P.H. Ribbe, editor

450 p.

6

MARINE MINERALS, R.G. Burns, editor

(1976)

(1980; revised 1982) (1979)

380 p. 52~ p.

7

PYROXENES, C.T. Prewitt, editor

8

KINETICS of GEOCHEMICAL PROCESSES, A. C. Lasaga and R.J. Kirkpatrick, editors (1981)

391 p.

AMPHIBOLES and OTHER HYDROUS PYRIBOLES - MINERALOGY, D.R. Veblen, editor (1981)

372 p.

9B

AMPHIBOLES: PETROLOGY and EXPERIMENTAL PHASE RELATIONS, D.R. Veblen and P.H. Ribbe, edLtozs (1982}

390 p .

10

CHARACTERIZATION of METAMORPHISM through MINERAL EQUILIBRIA, J.M. Ferry, editor (1982)

9A

11

CARBONATES,

(1980)

502 p.

R.M. Reeder, editor

(1983) ii

397 p. In press

FELDSPAR MINERALOGY FOREWORD In October

TO THE SECOND EDITION

1975 a Short Course

on Feldspar

Mineralogy

was held at the

Hotel Utah, Salt Lake City, in conjunction

with the annual meetings

Mineralogical

A. Yund, David B. Stewart,

Society

of America.

Richard

V. Smith and Paul H. Ribbe presented powder

diffraction

methods

study of feldspars the nine chapters published titled

and presented

by the Mineralogical

reflect

cluding Volume

optical

techniques

eight lectures,

of which became That book was

the series "Reviews

5 (1st and 2nd editions), written without

of its series en-

in Mineralogy"

of the volumes, this volume

presentation

from the M.S.A.

and a forthcoming

tion, was slowly taking

the present

with resulting

full responsibility

and new contributions

because

shape, no volume on feldspars

Unfortunately

revised

cost

dissatisfaction

Eleven

(see p. ii). Mineralogy

when its

as this, the second edi-

has been available

volume was advertised of patrons.

for this; hopefully

one on

at a short course.

at reasonable

That was a mistake,

to more

some of which __ in-

Three years ago it was decided not to rep rLn t Feldspar second press run sold out.

accepts

to the

Mineralogy.

Society as the second volume

renamed

are now available

were accepted,

and

as applied

the substance

of Feldspar

the scope and contents

fluid inclusions --were

two years.

Joseph

on x-ray single-crystal

Notes".

In 1980 the M.S.A.

volumes

and electron

of the first edition

"Short Course

accurately

workshops

of the

for

and orders

The series editor

the updating,

in this edition will in part compensate

improvements, for the incon-

venience.

It will be noted by readers new ideas appearing by review research greater

in Chapters

(other than ourselves) community.

Inevitably,

topics, some repetition

structures

and diffraction

libria and exsolution editor has attempted throughout

emphases.

the volume

received

of material

scrutiny

tests of time in the decided

the

soon to be outdated.

goals of individual

authors

has occurred,

in their

although

and their Al,Si distributions,

are featured,

to cross-reference as feasible.

books of this series produced with the detailed

practical

usually

Chapters· 1, 2, 9 and 10, in which plagioclase

patterns

textures

that there are many

in this, but the editor

a review volume

given the different

with quite different

with feldspars

nor survived

There is some danger

risk was to produce

assigned

experienced

3, 4 and 5 that have neither

are notable

This is a luxury not afforded

compensates

in other

and it, together

to some degree for the lack

of an index. Paul H. Ribbe Series Editor Blacksburg, VA April 30, 1983 iii

The

these and as many other subjects

with a short course deadline,

Table of Contents,

phase equi-

in this regard.

ACKNOWLEDGMENTS Throughout these

by Joseph debted many

this book

are Volumes V. Smith

to Drs. figures

following

repeated

and published

Konrad

We also for of

(and hopefully

discussions

pitch,

of which

none

scientific authors

progress.

are

in advance

lent

great

and Ada

of Geological

University

are

viding

thanked

rewriting, facilities

text

at the M.S.A.

edition

of Feldspar

Carnegie

of the

figures:

benefitted

of which

and criticized

many

are

patience

and

Mineralogy,

with

The

for data

for perseverance

and her

him

during

of the

and

State

the long process

of the University

abuse

two years

for excel-

staff

Institute

acknowledged,

much

staff

the secretarial

Support

suffered nearly

for figures,

Polytechnic

is gratefully

a high

some palpable

and correction.

Chiang

at Virginia

who

produced

to be commended

Sharon

from numerous reached

of the chapters.

scientists

and composing.

office

greatly

some of which

and several

colleagues

for their

Institution

Longmans Springer-Verlag

and

Sciences

(and salary!)

friends

and publishers

Journal of Geology Philosophical Magazine Proceedings of the Japan Academy Petrographische Mitteilungen Manchester University Press

Simmons

the

editing

in-

to reproduce

to reprint

for encouragement

The editor's

Department

the editors

individual

and

in typing

draftsmanship.

writing,

read

to numerous

Strickler skill

for permission

B. Stewart,

to blows,

of publication,

Margie and

David

Stewart

grateful

written

We are particularly

permission

this volume)

with

came

(1974a,b); work

Science The American Mineralogist francaise d~ Hineraiogie et de Cristallographie Contributions to Mineralogy and Petrology

re c e

The Feldspars Geochemical Transport and Kinetics Rock-Forming Minerals Electron Microscopy in Mineralogy

The editor

thank

their

Geochimica et Cosmochimica Acta Mineralogical Journal, Japan Physics and Chemistry of Minerals Schweizerische Mineralogische und

stimulating

to Smith

an encyclopedic

and H. Wiebking

and books

The American Journal Bulletin de La soc Chemical Geology

are made

Minepals,

by Springer-Verlag.

Springer

free of charge.

journals

references

2 of Feldspap

1 and

of

in pro-

as are his A.G.D.

over

back-orders

for this

overdue.

SELECTED REFERENCE WORKS The following lished

in

is

a list

recent

of

Feldspar

Minerals,

1.

Crystal

Feldspar

Minerals,

2.

Chemical

Verlag: The

works

New York.

627

Structure and

and

690

Solutions Solides en Min~ralogie, Edited by G. Saba tier (1974). Microscopy

Berlin. Thema

on feldspar

mineralogy

pub-

and

Physical

Textural

Properties,

Properties.

By Joseph

V.

Smith

(1974),

Springer-

pp. Institute, Manchester

Manchester, University

England. 1972. Press: Manchester.

pp.

Electron

525

in

Soc.

Edited

International

franc. by H.-R.

du C.N.R.S.

Min~raZ.

cri.etial.loqv-

Wenk and

G.

Thomas

No. 234, Orleans, 97,89-404. (1976).

1974.

Springer-Verlag:

Sohuei zeri-eche

Mineralogische

und Petrographische

Mitteilungen

47/1,

pp •

Rock-Forming

Minerals,

Longmans: Proceedings Christie

London. of

the

Framework 1-178.

317 of Edited

Silicates.

Study

Norsk Geologisk

--Phase Relations. Translated from

Jerusalem. Proceedings

4. pp.

NATO Advanced

(1962).

Feldspars Marfunin.

1983.

Co Ll.oque

euu:

Mineralogy.

pp.

Pe Ld sp a t e , 1967.

398

The

reference

Feldspars, Proceedings of a NATO Advanced Study Edited by W. S. MacKenzie and J. zus sman (1974),

717 Les

useful

years:

the

By W. A.

Institute

Tidssk:rift

Optical 1962

Deer,

of

Feldspars,

42/2,

606

R.

Olso,

A.

Howie,

1962.

and

Edited

J.

Zussman.

by

O.H.J.

pp.

Properties, and Geological Distribution. Russian edition, 1966. Israel Pr og . Sci.

By A. S. Translations:

pp ,

a NATO Advanced by W. L. Brown,

Study

Institute

untitled

at

on press

iv

Feldspars time.

and

Feldspathoids,

Rennes,

France.

FELDSPAR MINERALOGY TABLE of CONTENTS Page COPYRIGHT; LIST OF PUBLICATIONS

ii

FOREWORD TO THE SECOND EDITION ACKNOWLEDGMENTS;

CHAPTER

iii

SELECTED REFERENCE WORKS

iv

1.

The CHEMISTRY,

STRUCTURE

and NOMENCLATURE

P.H. RIBBE of FELDSPARS

INTRODUCTION

1

TOPOLOGY OF THE FELDSPAR TETRAHEDRAL FRAMEWORK

2

The a-axis projection

3

The e*-axis projection

6

The b-axis projection

6

Idealized cell parameters

9

PATTERNS OF ALUMINUM, SILICON ORDER-DISORDER: NOMENCLATURE BASED ON STRUCTURE AND CHEMISTRY Alkali

(Na,K) feldspars with Al:Si

Ca- and Ba-feldspars with Al:Si

=

=

9

1:3 and e ~ 7 K

2:2 and e ~ 14

9

K

12

I2/c eelsian pi anorthite Ii anorthi te

14 14 16

Summary of feldspar site nomenclature Antiphase domains and the

CHAPTER

Ii

17

average structure

2.

19

P.H. RIBBE ALUMINUM-SILICON ORDER in FELDSPARS: DOMAIN TEXTURES and DIFFRACTION PATTERNS

INTRODUCTION SEQUENCES OF Al,Si ORDER IN ALKALI FELDSPARS Ordering in K-feldspars

. . . . . . . . . . . ..

involving a monoclinic+triclinic

inversion

Development of polysynthetie tioinein mieroeline Untlilinnedor simple-tlilinnedmieroeline One-step or tiao-etiepordering? Temperature seale for the sanidine+mieroeline inversion Ordering in triclinic alkali feldspars Potassium feldspar Sodium feldspar

21 22 22 24 28 28 30 30 30 30

Page

CHAPTER

2, continued

SINGLE-CRYSTAL DIFFRACTION PATTERNS OF PLAGIOCLASES • . . • • . . . •. X-ray techniques

31 32

The preeession method The oseillation method

32 32 33

Summary of plagioclase diffraction patterns

39

SEQUENCES OF Al,Si ORDERING IN PLAGIOCLASES

40

Ordering in sodic plagioclases

40

Albite Peristerites

41

Average structure models of plagioclase

42

Ordering in calcic plagioclases

44

44 48 48

Anorthite Bytownite High plagioelases Huttenloeher intergrowths

49

Ordering in plagioclases of intermediate composition

50

'e '-plagioelase B~ggild intergrowths

51 54 54

SUMMARY .

CHAPTER LATTICE

50

o l iqocl.aee

3. PARAMETERS,

H. KROLL & P.H. RIBBE COMPOSITION

and Al,Si ORDER in ALKALI FELDSPARS

INTRODUCTION

57

TETRAHEDRAL SIZE AND Al,Si DISTRIBUTION

58

A linear model

58

A new model

67

Correction of bonding effects

69

LATTICE PARAMETERS OF ALKALI FELDSPARS

70

Alkali exchange series

70

Cell volume and the a dimension

74

The band

75

e cell dimensions

THE b-e PLOTS TO DERIVE (tlo + tIm)

77

THE a*-y* PLOT TO DERIVE (tlo - tIm)

79

STRAINED FELDSPARS

81

• • . • . . • • •

THE [1101 METHOD FOR DETERMINING Al,Si DISTRIBUTIONS

84 85

Basis of the [110] method The [110] method for alkali feldspars

87

Diagrams to estimate tlo and (tlo - tIm)

89

vi

CHAPTER

3, continued Page

ESTIMATION OF ERRORS OTHER DETERMINATIVE

93 METHODS

94

PETROLOGIC APPLICATIONS

96

Ordering paths

96

Suggested convention for plotting Al,Si distribution data

98

CHAPTER

4.

H. KROLL LATTICE PARAMETERS and DETERMINATIVE METHODS for PLAGIOCLASE and TERNARY FELDSPARS

INTRODUCTION

101

LATTICE PARAMETER VARIATION

103

High plagioclases

103

Low plagioclases

106

Thermal expansion

107

THE [110] METHOD FOR PLAGIOCLASE FELDSPARS

•••••••••

e .••

110

Diagrams to estimate tlo and (tlo - 1 µm) to be seen in thin section (where it is sometimes mistaken for fine scale twinning). An electron diffraction pattern of an exsolved specimen of bulk composition An72_75 (Fig. 12) was discussed in the previous section. It is remarkable in that it shows nearly every type of diffraction phenomenon known to occur in the entire plagioclase feldspar series.

The sharp 'a' and 'b' and diffuse 'c'

and 'd' reflections arise from the transitional anorthite (An~90)' which undoubtedly has hundred Xngstrom scale 'c'-domains and coarser 'b' domains (see table above). The average structure of the more sodic phase, an 'e'-plagioclase of composition An~65' has lattice parameters very close to those of An~90' thus its 'a' reflections superpose on those from the calcic phase.

The antiphase super-

structure which produces 'e' and 'f' reflections is imaged in Figure l3b; in this particular specimen the periodicity ranges between ~32 and ~37

X

due to

compositional inhomogeneity, which may represent a secondary stage of exsolution. In general, the two exsolved phases coexist as complicated lamellar intergrowths on the scale of a few hundred Xngstroms to optically visible (micronscale).

The's'

streaks through the 'a' reflections (Fig. l2) are inclined to

b* and c* and are approximately normal to (031); they result from the imperfectly developed (031) quasi-periodic lamellar "superstructure" of alternating slabs of calcic and 'e'-plagioclase, like those illustrated in Figure l4-l6 in Chapter lO.

A second lamellar set parallel to (301) is sometimes observed.

X-ray patterns never give clues to the orientation of exsolution lamellae, but if the average total thickness of an An~65 1350 to 2400

X,

+ An~95 pair is in the range of

interference colors may be visible from a plane which is paral-

lel to their interface (see Ch. lO, pp. 266-270).

49

Ordering in plagioclases of intermediate composition First we will discuss the structures of two low plagioclases which showed only 'a' reflections in x-ray photographs. Oligoclase.

Average structures of two oligoclases, Anl6 and An , were 28 reported by Phillips et al., (l971). It is assumed from their pegmatitic occurrences that they are as ordered with respect to Al and Si as is possible, and indeed their diffraction patterns, lattice parameters (Chapter 4) and optical properties (Chapter 5) indicate structural states consistent with low-temperature equilibration.

However, their Al,Si distributions are far from ordered

in either the low albite or

pI

anorthite sense.

Data are shown in Figure l6

and recorded in Table 1, Chapter 3. Because T10 is Al-rich and the other three T sites are equally Si-rich, it is clear that, just as in albite, Al concentrated in TlO as these feldspars inverted from their respective disordered arrangements.

But tlo is signifi-

cantly less than l.O in both An16 and An28, even though there are l.16 and l.28 Al atoms available in these structures to fill TlO. This is one limiting model for low plagioclase -- we will call it "full T 10".

Another possible model in-

volves mechanical mixtures of the two fully ordered end members of the plagioclase series, low albite [LA; tlo =1.0, =~(tlm+t20+t2m)

= 0.0) and anor-

thite [An; tlo =tlm=t2o =t2m=0.5; Eqn. 2 above). The Al distributions expected from these are listed below in contrast with the "actual" values determined from crystal structure analyses using Equation 5, Chapter 3. nAn = 0.16

Model tlo "full tlo" mech'l mix "actual"

1.00 0.92 0.815

nAn = 0.28

tlo

0.053 0.08 0.115

1.00 0.86 0.68

--_---

0.093 0.14 0.20

Clearly there must be an ordered LA structurql "component" to account for the concentration of Al in TlO, and an anorthite structural "component" to account for the observed composition, and, in order to raise the Al content of Tlm, T20, T2m to the "actual" tlm, t2o, t2m values; one might add a third "component" that consists of disordered albite (call it analbite, AA) which in turn must be subtracted from the LA "component" to keep the formula balanced.

If

the fraction of anorthite "component" in such a model is given as nAn' then the fraction of AA is 4[obs - ~An) and the fraction of LA is [1 + nAn - 4obs). For low Anl6 and An28 the values are l6:l4:70 and 28:24:48, respectively. To explain the observed Al,Si distribution of these and other low 50

plagioclases, Smith and Ribbe (1969) proposed a model similar to this but which involves coherent out-of-step domains, on the scale of ten or more Xngstroms, consisting of alternating ordered LA-like and An-like structure in a continuous tetrahedral framework.

Between the two types of ordered structure are bounda-

ries in which some degree of Al,Si disorder must exist because of the topologic incompatibility of the 1:3 and 2:2 ordering patterns. tributions in the four T sites of the Cl, 7

X

The reported Al,Si dis-

cell represent an average of

that which exists in these domains and the disordered boundary regions separating them.

This model is discussed in more detail below.

'e '-

.... ....

•

0 E NO

•

o

N

k

+)

+ E

t..

(I...

",,"""'C +l

E

Q) ..

o

.-t

II

Q)

.: ~ '" Q)

.c .... ...

...o '"

Q) U

c: co

~"

....

" co

Q)

.... U 0

o

'"

c:

~

.... CD

a. '"Q)

'tJ III

'"

U

'tJ

co a.

.... co

:J U U

co

'c:

>. ....

c

0000

....

~

~

c:

>-

....

:::J

m

o

0

c: co

...

......

....:J

0000

N

Q) U

o

rl

..

IJ)Lt1Ln ..-00'\ ..-NN

-o

o

'"

'"

c:..c.

>-

"

C 0

m

.

V

Lt1UiU1L{} nn..;:to NNNN

E ~ 0.:

Q)

.,µ ·rot

m

1:J x..µ

t"-t"-t"-t"-

00lf)Lt1 0000 0000

tn

....c: ...co

Q) E

rn

'"

o

-..-I

u

ro

c:

s:

0

oot")t")nLDU1Lt1LnO\ "-L[)lf)lJ1U1U1U1U1lf) 1.0\.0\0\01.01.0\0\01.0

o

........

'.-4

+)

Q)

V 'tJ

(l • ....

.......

+)

m

rllM ~

l-.....

•

...

co a.

"'C

tU

s:

U)

U U

m .... ..... "'C

m

s:

'"

k

E E Q) N N.c

.L:..c.c:J

1:J ..µ

'"

....

Q)

..j..J

m

r-4

1:J ..µ

'"

en

.>.>.>. [IlCO[DCO

.......... .r:.r:.r: .......... ... ... Q)

Q)

Q)

•..-l ...... ..-l

...

000

c: c: c: cc e; < mlno N

N

t"J

'"

'"

_0\

_en

U")q

U")q

qO \0 U") \O~

.0'" o>r-

0.:

~

~I

';,', "'-

1

ttl'

: I "I 0

co ..... 000'\

co com

r-- ..... rom

",roen

00 00

t"1C'0'\ 0

"' en

00

en en

en en

N~

r-O

r-O

r-O

co CD en

"'''' NO

o>~ N co

CD ",en CDN

lll

in

o ~o> CD

tn

N

N

OlN 1'1r",r-

NO

"'N Ol~

coo

'"

co

r-N Ol~ U'l~

'"

o eno Ol'" U'l~

NU'l N~

CD co co en r-N Ol e-

'"

en "'en Ol e-

Ol ~O ~O ~

a> .µ

"

c

c

~I"

rl

a> u,

E a>

....

c:

o

a> .µ

c: N

c

E

c

E

N U

'" u

a.

E

'tJ

N

a. c

" '"

'"

o

u r-

U'l 1'1

....E"

...."

E

...."

E

..,"

E

E

E

E

E

...."

E

E

...."

...."

...."

...."

a>

a>

c:

c

U'l

a>

c

a>

c

co

66

a.

""

'" ....c"

...."

E

c

::J

N

E :3

o

..J

...."u

E :3

o -'

for anorthite, 1.613 and 1. 742

A

for low albite (Table 1;

average of four refinements), and 1.613 and 1.738

A

for low microcline

«AI-O»

= 1.747

A

(Table

3 and Blasi et al., 1983; average of five refinements). The «T-O»

versus diagram (Fig. I) covers the range from 0.25 to 0.5

Al/(Al+Si), and even if the bonding effects just mentioned were insignificant, long extrapolations from 0.25 to 0 and 0.5 to 1.0 would be necessary to represent the full range of t values in individual tetrahedra.

This leads to sys-

tematic discrepancies, and Smith (1974a, p. 70) "in desperation" suggested using two separate straight lines in the regions of 0 to 0.5 and 0.5 to 1.0 Al/(Al+Si), but with limited success.

Direct refinements of site occupancies

by neutron diffraction methods are few in number and not without their own difficulties (see footnote 1). A new model Ribbe (1975, p. R-22) suggested deriving Al contents of T sites, not from the distances themselves, but from differences in mean distances.

His

method eliminated some uncertainties of the linear models that arose from long extrapolations and from the fact that the mean AI-O and Si-O distances are different in the different ordered structures, namely but did not account for bonding effects.

LA, LM and

pi

anorthite,

Furthermore, it did not permit an

independent determination of Lt apart from a knowledge of nAn (see Eqn. 3). This last problem may be overcome by considering the differences between average individual and grand mean tetrahedral distances, i.e., «T-O»,

rather than size differences among individual tetrahedra as in

Ribbe's model.

The procedure for calculating site occupancies may be recast

into a single equation if we consider separately the difference 6t between the individual and the average values of t: 6t

=

t. -

or

1.

ti

=

+ 6t .

(4)

is found from chemical composition by Equation 1, and 6t is related to - «T-O»,

so that Equation 4 becomes ti

where 'const'

=

=

«Al-O»

0.25(1 + nAn) + «Ti-O> - «Si-O»;

spars and is taken to be 0.13

A

- «T-O»)/const

it is equal to 0.125

X

,

(5)

for K-rich feld-

for Na-rich feldspars and plagioclases.

At this stage, the An-content still must be known in order to find ti. Figure

However, we can-eliminate this by expressing in terms of «T-O».

1 indicates that the linear model must be modified for this purpose by (1) treating the An-rich plagioclases separately, and (2) considering that the

67

«T-O»

distances of ordered feldspars --especially

alkali feldspars and souic

plagioclases -- are slightly larger than those of their disordered equivalents. Since it is desirable to substitute by «T-O»

in Equation 5, we chose

as the dependent variable in a regression analysis of the data listed in Tables 1, 2 and 3 (excluding An-rich plagioclases): = 0.25(1 + nAn) (6)

-11.215 + 6. 981 «'['-0» + 0 .124 «T I0-0> - (±.076) (±.017) I with a correlation coefficient given in parentheses. order present.

r2 = 0.996.

Estimated standard deviations are

The third term on the right accounts for the amount of

When TIO and Tlm tetrahedra are identical in size, Equation 6

reduces to the original linear model.

The values of expected from chemical

composition are reproduced with a standard deviation of +0.005 Al/(AI+Si), responding to

±

cor-

2 mol % An.

An analogous equation for An-rich plagioclases

The reason why «T-O»

=

is (7)

-12.088 + 7.491 «T-O»

distances of An-rich plagioclases

be expected from sodic and intermediate

compositions

are larger than would

is open to question.

One

is tempted to ascribe it to some bonding effect due to Ca, but the substantial discontinuity fined in

II

pi

near An in Figure 1 is disturbing, as is the fact that An98 re80 by Bruno et al. (1976) gave «T-O» = 1.681 A, but refinement in

gave 1.678

A.

Combination occupancies sition.

of Equation 6 or 7 with Equation 5 allows uS to derive site

from distances without making reference to chemical compo-

This procedure is indicated when the total Al content so derived is

to be checked against the Al content expected from the chemical formula: should not differ by more than 2 mol % An.

To simplify calculations,

they

it is

safe to assume that tIm = t plagioclases microclines

(Table 1; cf. (Table 2; cf.

0 = t m for all natural Na-rich feldspars and 2 2 Fig. 16, Ch. 2) and t20 = t2m for intermediate

Fig. I, Ch. 2).

A sample calculation

for inter-

mediate microcline AID (#5, Table 3) follows.

for T 0 = 1.673, TIm 1

= 1.651, T20 = 1.623, T2m - 1.622

0 = 0.25 + (1.673 1 tIm = 0.25 + (1.651

t

and

t

2

0

1.642)/0.125 = 0.50 1.642)/0.125 = 0.32

= t2m = 0.25 + 0.6225 -l.642)/0.125

68

A;

= 0.09

«T-O»

l.642 A

Correction of bonding effects As mentioned

earlier, a statistical

study of bond length variation in

feldspars by Phillips and Ribbe (1973a) and Ribbe et al.

(1974) produced three

factors, in addition to Al content, which perturb individual T-O bond lengths:

A

(I)

Linkage

Si-O ~ Si bonds are ~0.03 Si-O -+ Al bonds.

(2)

Bonds to Na,K,Ca

The coordination number (2, 3 or 4 in feldspars) of the oxygen atom is related directly to T-O distance.

(3) T-O-T angle

longer than

Longer T-O distances are associated with narrower T-O-T angles.

Strob (1983) has completed an elegant study of alkali feldspars in which he has produced regression equations to correct for these effects. to observed distances reach !0.005 standard deviation in .

Adjustments

about three times the estimated

Their importance is that they adjust for what are

small, but obviously systematic, individual tetrahedra.

A,

errors in our estimation of Al contents of

They have less importance in our subsequent discussion

of the derivation of ti values from lattice parameters

than they do for model-

ling the precise details of Al,Si ordering paths, for example, that are shown in Figure 8bin Chapter 2 for Na-feldspar.

The effect of these is to slightly

decrease the value of and increase

and thereby redistribute

estimated Al contents, for which Strob has derived a somewhat modified version of Equation 5. K-feldspars

Two examples suffice to illustrate the results for Na-feldspars;

are generally much less affected. Observed ~_m~

Tiburon HA #'; in Toble I

Site

F99 »F91.

c To

determine aestimated from b·c, use the following regression equation: 1

aest = 8.634 - (11.437 - 0.12226 b'c)1

6a

=

aobs - aest' as defined by Stewart and Wright. Stewart

(1975) comments, "The effects of certain components sometimes

and H 0+?) may be confused with the 3 effects of coherence, so that if a feldspar is known to be homogeneous and a found in alkali feldspars

(B, Fe, NH:,

significant 6a is observed, composition should be carefully checked. volume of a strained feldspar is only a first approximation

The cell

to the cell volume

BThe plane of intergrowth is close to (100). Thus in the potassic phase band C will be smaller than "normal," a will be larger, and vice versa in the sodic phase.

R2

MONOCLINIC

TR1CLINIC

692 A3) with various values tlo. The equation to start with was that for K-rich low alkali feldspars (Table 5), the slope and intercept of which was changed with tlo such that the straight line representing tlo =0.38 was parallel to the Nasanidine line.

Thus, the equation for the contours takes the form:

tr[lIOj Thus

tr[lIOj

IlTriclinic adularias, grown within the micro cline stability field, may deviate from this line. The equilibrium tl value of the sanidine + microcline inversion, which cannot be directly observed, can at least be approximated: sanidine from Volkesfeld, Eifel, has tl = 0.315, according to four structure refinements (Table 2); 'Spencer C' orthoclase has tl = 0.36. The equilibrium value can thus be assumed to be tl = 0.34±0.02.

89

Table 5. Variation of tr[lIO] and tr[lIO] - tr[110] with cell volume V in the limiting series analbite-high sanidine (AA-HS) and low albitelow microcl1ne (LA-LM) (Figs. 10 and 11): tr[lIO]

a

=

1

+ a2V and tr[110]

LA-LM series:

tr[lIO]

- b1

2

a

Coefficients

AA-HS series:

-

2

b

a '10 2

1

+ b2V. 1

b '10 2

V

< 692 R3

5.6103

0.30373

-.8393

0.12128

V

> 692 R3

5.4396

0.32747

0

0

V

< 692 R3

5.5129

0.28978

-.3813

0.09933

V

> 692 R3

5.0123

0.36213

0.6452

-.04902

I

780 776l

t10

..Al = 1.0. Data for a Lb t t e s from Hartin (1970, Table 1) are shown by circles, most of which f n Ll on the one-e tcp ordering path, and triangles, which do not. Nafeldspar snmo l c s 393, 1219 and 1216 (formed at 200-250°C) apparently have AI-enriched 7' m sites. It is po s s t bl e t hc se samp Lc s partially ordered meta stably with monoclinic symmetry befo~e becoming t r t c l Ln t c (see Ch . 2, Fig. 8). In t e rmcdin r o mi croc lines (solid Jots) studied by Guidotti, Herd, and Tuttle (1973) order along a path where ,\1 moves to TIO from TIm approximately q times [aster than f rom T 0 and 1'2m 2 c omb i n cd . The shaded area with 0 -= tIm d La cr amms t Lc a Ll y represents the relative abundance of l the monoc l i n n- feldspars [rom the s.3me region. Monoclinic feldspars from th-is area ordered further with mnl1~t;.H·

c,"

~c:,;

Or

~ /~~~~

0.20

Triclinic

I

I I I

I

0.30

(}W

a

0.40

uncertain

(1979 I ... Spencer

(1937)

Wondrotschek

O.A. P. II (010 I

O.A.P.(-I.L(OtO) O.A. P. .L (010)

(1981)

? Symmetry

A, B,C(htdl

Y1\f DePieri

)( 'J:f.. Preiss

Monoclinic

+ Zeipert

•

t;.

I

OF

o Monoclinic

;7

11'J:f../'A.vOC

"'I\~

l>u

(1981)

ye

t;.

'!f

----.--

~

t;.P 0

.

0,50

0y.o~

~«,

oc,V

7007

oB °z

~,c,~

KOV

:g

~.: oHIM

O.A.P.(-).L(OIO)------~---

I

I I

0.0

/,W-I

7002

:

I

I

'/'''''~

A

(010)

~«, ~;at~,\)'\~+~

;)

c:,"",./";

.-10-12cm2sec-l).

are simultaneously

is com-

to determine

et al., 1978).

a hole

the

One of the principal

if

(e.g., Giletti

and by assuming

technique

in order

and it gives large

near

can be determined. years,

feldspar

temperature,

A sectioning

annealing.

resolution,

is used to sputter

is subsequently tration

after

(>10-18cm2sec-l)

mined with an ion microprobe

can be implanted

thickness,

is relatively

can be determined

in the ion probe

1977).

a layer of known

tions of this method the diffusion

which

or the isotope

direction enables

method using

is to determine

the ion microprobe

the diffusional

as providing

a completely

anisotropy different

coefficients. 206

the isotopic

profile

(e.g., Giletti

in the crystal method

in a specific

et al., 1978).

This

to be determined,

for determining

diffusion

An important question with regard to the hydrothermal technique concerns how the isotopic exchange occurs.

In the original study (Merigoux, 1968), it

was assumed that only lattice diffusion contributed to the isotopic exchange unless the grains and fluid were out of chemical equilibrium.

When the Na/K

ratio of the feldspar and the fluid is far from equilibrium, the grains are reconstituted by a fine-scale dissolution and reprecipitation process (O'Neill and Taylor, 1967).

At high temperature, and probably at high pressure where

solubility is greater, the grains may be modified by dissolution and reprecipitation even if they are in chemical equilibrium with the fluid.

The amount

of dissolution and reprecipitation is temperature-pressure-time dependent, and the window for lattice diffusion measurements of ions in any mineral must be determined.

Untwinned and disordered overgrowths on grains of a maximum

micro cline were used to demonstrate that only lattice diffusion contributes to the isotopic exchange below about 800°C and 2 kbar water pressure (Lin and Yund, 1972). Additional proof that the rate of isotopic exchange between feldspar and fluid is controlled by lattice diffusion is provided by the different isotopic exchange rates for potassium and oxygen in the same feldspar at the same temperature and pressure (Yund and Anderson, 1974).

A difference in the rates

would not be observed if the exchange was due to a mechanism other than lattice diffusion.

Finally, there is very good agreement between the results

determined by the integrative and ion microprobe methods for potassium diffusion in low albite (Kasper, 1975; Giletti et al., 1974), and for oxygen diffusion in adularia (Yund and Anderson, 1974; Giletti et al., 1978).

If dissolu-

tion and reprecipitation significantly contributed to the exchange, the results from the two methods would not agree and the isotopic gradient would not be a diffusion profile. Inter-diffusion coefficients are commonly determined by bicrystal experiments in which two crystals of different compositions are polished and held together during the anneal (e.g., Christoffersen et al., 1981). concentration profile is measured with the electron probe.

The resulting

Diffusion aniso-

tropy can be determined by this method, and the principal limitation is that it is difficult to accurately determine D values less than about 10-14 cm2 -1

sec

_

[An ion microprobe could be used to determine smaller D values.]

Petrovic (1972) used a variation of this technique which involved the partial exchange of alkalis between a crystal and molten chloride. A recent technique for determining an average interdiffusion coefficient for a compositional interval is based on the rate of homogenization of 207

exsolution 1980;

lamellae

Brady

Electrical these

data

fusion ment

conductivity

of multiple

boundary

profiles

is used

is known. width,

charge

carriers

(Brady

to limit

across

to extract

the grain

The quantity

determined

and McCallister,

diffusion

in silicates, (Maury,

boundary

of this method.

the determination

of dif-

and a mathematical

diffusion

coefficient

Dgb times

boundary

coefficient

width

The

of which

boundary,

is actually

and

1968).

identification

the usefulness involve

a grain

of the grain

transport

coefficients

and the actual

measurements

in a sample

an effective

to ionic

diffusion

appear

diffusion

and the evaluation

Commonly,

and thickness

is related

is (are) functional

Grain

composition

in press).

can be used to estimate

possibility one(s)

of known

and Yund,

Dgb when

the grain

is rather

is used which

treatD

t

boundary

subjective.

is the product

of

Dgb and the width.

EXPERIMENTAL The feldspar were

perthitic

1952;

samples

Sippel,

1963).

for volume

sonably

good agreement

composite

ferent

diffusion. with

measurement studies

types

considered

not

any further

In the following

as identification

particular

diffusion

of the topics figures

provide

interval

was

ficient

normal

others

are in rea-

are clearly

diffusion.

and the effect

These

studies

Jensen,

of these

1963)

in detail,

meaningful

questions should

a

The samples

studies

only

results

evaluation

and problems.

be consulted

were

will

of the difnot be

in the text where

are arranged

by

of the data as well Some of the data are

for information

determined.

comparison

the data were

However,

about

the data

how

for some

they are discussed.

The

of the data and show the temperature

determined.

in feldspar

of sodium

diffusion

by Bailey

to (010) was

to (001), but within

(Sippel,

and volume

the experimental

coefficients

investigated

1949;

the validity

whereas

be evaluated.

a more

and these

of diffusion

data,

diffusion

here. discussion

a convenient

The anisotropy phere

recent

cation

(Rosenquist,

to evaluate

boundary

cannot

are presented

over which

Anisotropy

more

of remaining

in tables,

crystals

characterized

this permits

presented

of the earlier

Some of the results

of grain

were

of diffusion

topic because

in most

not single

It is difficult

studies

in these

used

or otherwise

RESULTS

in an albite

(1971).

He observed

0.1 to 0.6 as large

his experimental

error 208

at 595°C

and one atmos-

that the diffusion

as that for diffusion

these

diffusivities

coef-

normal

could be equal.

Petrovic normal

(1972) observed

to (010) than normal

fractures

and spallation

diffusion

rates

diffusion

normal

data,

normal

of that normal

to (001) and

in low albite

to (010) was one tenth

at 1000°C

that normal

and 15 kbars

to (010) is one tenth

alkali

parallel

we will

diffusion

half

expect

the diffusion

800°C

and 1-2 kbar

to (001), (spherical) Effect

(010),

(Ill), and

The early

hydrostatic

diffusion

parallel pers.

as the simplest

by

and normal

to [011]

comm.)

to that parallel

coefficient

normal

indicate to [011].

approximation

for

would

equal,

be the same

has been

et al., 1978).

1977)

The anisotropy

but

for these

The diffusion

is

of

it is reasonable

investigated

(130) are approximately

indicate

to (010) in a micro cline

to (001) in an orthoclase.

diffusion

pressure

studies

pressure pressure

of alkali

within

and the pressure at 1000°C

diffusion

coefficient

diffusion

experimental

range was

normal

that the activation

on alkali were

None of these

small.

(Christoffersen

3), and that the effect can be disregarded

and water

of 1-2 kbar.

diffusion

appears

results

adularia

interdiffusion

(Christoffersen, equal

by the normal

to

ions.

in two albites

coefficients

consistent

with

at

normal

an isotropic

model.

of hydrostatic

or a water

stant

(Giletti

of

sections.

anisotropy

of oxygen

between

that alkali

model

determined

Preliminary

interdiffusion

need not be numerically

that the relative

one hundredth

coefficient

(Misra and Venkatasubramanian,

of that normal

The anisotropy

but

The details

profiles

to (001) at 800°C.

use a cylindrical

diffusion

equal,

to unpublished

about

1974).

the diffusion

to [100] is about

in the following

that at 800-870°C

Sr and alkali

that

results

The data for Sr diffusion

only about

to

the alkali

about

In reference

to (001), with

Preliminary

that interdiffusion

that

were

(Petrovic,

also indicate

that normal

intermediate.

difference

to (010) was

that potassium

indicate

et al. (1981) for alkali

Christoffersen

Nevertheless,

slower.

is slower

published.

et al., (1974) reported

Giletti ion microprobe

being

(110) of adularia

somewhat

not been

this

He also reported

to (110) at 890° and 1000°C have

in an albite

to (001), but he ascribed

that Ln t.er dif f us Lo n normal

experiments

albite

interdiffusion

of the crystal.

to (120) was

he reported

these

that alkali

either studies

done

at one atmosphere

observed

error,

but other

A more

recent

any effect

factors

study

were

of alkali

et al., 1981) found no difference

to (001) between volume

diffusion

for alkali

of hydrostatic

pressure

in most mineralogical

209

of

not coninterin the

five and 15 kbar.

Thus,

diffusion

(see equation

is small

on alkali

applications.

diffusion

it

in feldspar

The effect

of water

is somewhat

coefficients

determined

1972)

appear

to be consistent

other

factors

are taken

into account.

tion lamellae

in alkali

feldspar

samples

are annealed

1978).

Goldsmith

attainment alkali

answered.

section).

confining

pressure

have been

800°C

for several

before

dicating

that the trace

of water

diffusion

1 and plotted

data.

The high-temperature and albite

chlorides.

These

Data agreement

800°C

for high

salt experiments

was vacuum

when

the

experidried

(Christoffersen, for an undried

for Na and K, which

1, show

good agreement

disagreement

data were were

have

at

pers. sample,

sample

in-

did not

temperature

those

a lower

in some respects

Na diffusion

K diffusion

for adularia

in orthoclase

210

assumptions

profiles

alkali of magnitude) of ideality

(curve

8) are in fair

shown by curve (curve

as given

energies

diffusion

molten

on composition.

in adularia

in orthoclase

the activation

with

and include

and poor

temperature

(up to an order

coefficient

in

some of the high

from alkali

exchanged

precision

data,

for Na diffusion

However,

are summarized

is between

calculated

partially

temperature

that for K diffusion

interval.

diffusion,

interdiffusion

which

the

(see later

is only effective

wt %) in the undried

of the self-diffusion

ly, the high-temperature ment with

the molten

Alkali

those

affects

oxygen

2, 4 and 8 in Fig. 1) and the lower

which

results

of the lower

with

that

in

completely

temperatures

the Pt tube

(~.02

diffusion

greatly

enhances

of water

a bicrystal

coefficients

(curves

in adularia

than most

on the

rate may not be

on alkali

to lower

kilobars.

agree with

The greatest

results

and independence

the

at 15 kbar.

on Figure

in others.

temperature

the

coefficients

The self-diffusion

agreement

enhances

experiments

of water

greatly

creep

sealing

results

Table

feldspar,

several

The preliminary

diffusion

greatly

not be considered

amount

or that a trace

is above

hours

of water

probably

must be considered

comm.).

Alkali

that water

in reversal

done at 15 kbar with

the alkali

when

exsolu-

(Yund and Davidson,

this reaction

of dislocation

of water,

affect

pressure

to be the same whether

pressure

although

that even a trace

The possibility

ments

Lin and Yund,

of coherent

at 10 kbar

should

rate of alkali

the field

traces

appears

lack of effect

the question

contained

1974;

The rate of growth

report

solvus,

of the apparent

disordering

1972,

diffusion

diffusion.

It is known

and extends

Alkali

done at 1-2 kbar water

at S60°C

equilibrium

by lattice

In spite

(Petrovic,

those

(1974)

strain-free

most experiments,

problematical.

in air or at 2 kbar water

of chemical

controlled

salt

with

and Newton

feldspar

Al/Si

in molten

more

9.

Similar-

2) is in fair agree-

by curve

for these

3 in the 600-

two sets of data

·16-1 ~ 0 0

=

::. ::. 0

2

.. 0

.

::.

::.

::.o

~

0

30000

cm-t

20000

,---L---

15000

y

6

ORTHOCLASE ITRONGAY

4 W U

Z