on oriented titanite and rutile inclusions in sagenitic biotite

8/20/2019 On oriented titanite and rutile inclusions in sagenitic biotite

1/13

American

Mineralogist, Volume

76,

pages

1205-1217, l99I

On oriented

titanite and rutile inclusions in

sagenitic biotite

YrN-HoNc

Snnu

Department

of Geological

Sciences,University

of

Michigan, Ann Arbor, Michigan 48109, U.S.A.

HouNc-Yr Y,tNc

Department

of

Earth

Sciences,National

Cheng Kung University , Tainan,

Taiwan 70101, Republic

of China

DoNar.o R. Pplcon

Department

of Geological

Sciences,

University of Michigan, Ann Arbor,

Michigan 48109,

U.S.A.

Arsrru.cr

Well-oriented,

needlelike

nclusions

occurring n sageniticbiotite

in

an orthogneiss

rom

the Tananao

complex, northeast

Taiwan, have

been studied by optical

microscopy, trans-

mission

and

analytical

electron microscopy,

and electron

microprobe

analysis.

Titanite

needles

n three

orientations

combine to form

equilateral triangles,

and

rutile needles n

three

other orientations

generally

ntersect

o form asterisk-shaped nits.

Titanite needles

are elongated arallel o (01 ). They are orientedwithin

{001}

ofbiotite, and one ofthe

three

sets,which intersect

at angles f60", is

parallel

o a ofbiotite.

The

{lll}

or

{433}

planes

of titanite

are approximately

parallel

to

{001}

of biotite.

Rutile needles

are

elon-

gated

parallel

o c, and rutile

{

100} s

parallel

o

{001}

of biotite. Of the three

setsof rutile

needles

ntersecting

at angles

of60", one s

parallel

o b ofbiotite.

The

preferred

orientation

of rutile inclusions

in

biotite is in

accord

with

their

mutually

parallel planes

of

closest-

packed

anions and chains

ofedge-sharing

octahedra.

Titanite inclusions contain approx-

imately

0.

0

(Al

f Fe)

per

formula

unit, have space

group

A2/a, and

give

electron dif-

fraction

patterns

that display

streaking

along b* and c*.

Rutile inclusions contain 0.2-0.3

wto/o

FerO.

(total

Fe

as FerOr),

exhibit

streaking and splitting

of reflections

n

electron

diffraction

patterns,

and display

a

planar

microstructure

parallel

to

{

100}, which

appears

to consist

of

precipitated

platelets

hat have

the

hematite

structure and a

probable

com-

position (Fe,Ti)rOr. The titanite and rutile inclusions are inferred to have topotaxially

precipitated

through

reactions

occurring

during

retrogressivemetamorphism

when

excess

Ti

and

Ca

were

derived from

biotite of igneousorigin.

INrnooucrroN

The

term

"sagenitic

texture" refers

to

the occurrence

of slender,

needlelike

nclusions

intersecting

at

anglesof

60'and

included

in

phlogopite, quartz,

or

other

minerals

(e.g.,

Gary etal.,1972).

Although

suchacicular nclusions

have long

been thought

to consist of rutile,

titanite, he-

matite, tourmaline, zircon, apatite, or allanite (Moor-

house,

1959;Winchell,

l96l;

Rim5aite,

1964:Rimsaite

and Lachance

1966;Niggli, 1965;

Gary

et al., 19721'Deer

et al.,

1982),

hey

have

not

been completely

character-

ized. The most

extensive

study of

sagenitic exture was

carried out

by NigSli

(1965),

who

used

electron micro-

probe

techniques

o analyzesagenitesn

biotite from

plu-

tonic rocks

and

gneisses

nd concluded

hat most

ofthem

consist

of titanite

but that some were

rutile. Some well-

oriented nclusions

n the cores

ofphlogopite

grains

from

a marble were

identified

optically

as rutile

(Rim5aite

and

Lachance, 1966).

Titanite

or rutile inclusions

have

been

observed n

biotite or

phlogopite

(Rimsaite,

1964;

Rim-

Saite

and

Lachance,

1966;

Niggli, 1965)

and in

chlorite

produced

by hydrothermal

alteration of biotite

(Rim-

saite, 1964;Ferry,19791, arry and Downey,

1982;

Veb-

len

and

Ferry, 1983;Eggleton nd Banfield,

1985).

Sageniticbiotite

occurs n the

grreisses

fthe

Tananao

metamorphic complex on the

island

of

Taiwan. This

complex consists

of

pre-Tertiary pelitic

schists,

marbles,

gneisses,

metabasites, mphibolites,and serpentinitesand

crops

out extensivelyalong he easternslopeofthe

north-

trending Central Mountain Range. Lo and Wang Lee

(1981) performed

X-ray analyses f the

inclusions

ex-

tracted from the sageniticbiotite

and reported that they

were

titanite and

sillimanite.

To

characterize hese

nclu-

sions better and to establish heir structural

and

crystal-

lographic relations with the host biotite, samplesof sage-

nitic

biotite

were collected

from

a

pre-Tertiary

orthogneiss

near the village of

Pihou, northeast Taiwan, and studied

by optical microscopy, transmission

and analytical elec-

tron

microscopy

(TEM

and AEM), and electron

micro-

probe

analysis

(EMPA).

OnsrnvlrroN

By

oprrcAr,

MrcRoscopy

The orthogneissofthe

present

nvestigation

s

generally

medium to coarse

grained

and

has a

granitoid

texture.

It

0003-o04x/9

/0708-l205$02.00

t205


2/13

t206

SHAU

ET AL.:

ORIENTED

INCLUSIONS

IN BIOTITE

Fig.

l.

(a)

and

(b)

Photomicrographsof two sageniticbiotite

flakes.Titanite

(T)

needles orm equilateral

rianglesand

rutile

(R)

needles orm

asterisks

n

the biotite

host.

One of the equilateral

rianglesand one

of the asterisks

are ndicated

by white solid

lines.

The

a and b axes of biotite

were

chosenarbitrarily using one of

the three directions

of titanite and

one of the three

directions of

rutile

prisms,

respectively.Plane-polarized ight.

is composedof sodic

plagioclase Anro-or),

uartz,

biotite,

and

minor

amounts of

muscovite,

potash

feldspar, apa-

tite, titanite

(intergranular),

garnet,

chlorite,

ilmenite, and

trace

amounts of calcite,

which

generally

occurs as small

inclusions

(l-20 pm

in

diameter)

lying along the

parting

planes

or cleavages f

plagioclase.

The biotite commonly

exhibits

well-developed sagenitic texture.

Some biotite

grains

are overgrown by chlorite

or

have layers interca-

lated

with

chlorite.

No

sagenitic

nclusions

have

been

ob-

served

n

chlorite.

However, a

few isolated

anhedral

ti-

tanite

inclusions

up

to l0

pm

wide and 40

pm

long have

been observed in chlorite, with their long dimensions

subparallel

o

{001}

ofchlorite.

Subhedral itanite

grains

up to

I mm long also occur at

the interyranular sites

among other

major

phases.

The sagenitic exture can

best be examined

in

{001}

sections

of biotite.

Very

thin

{001}

sheets an

easilybe

peeled

from a biotite crystal,

and the

following charac-

teristic

features

of sagenitic

texture can be

readily ob-

served

n immenion oil

with

a

polarizing

microscope

Fig.

l). Needlelike

nclusions

0.1-2

p.m (most

are


3/13

SHAU ET AL.:

ORIENTED INCLUSIONS

IN BIOTITE

Taele 1. AEM

analyses

of

rutile

and

titanite

inclusions

n

biotite and biotite

from the Tananao

orthogneiss,

northeast Taiwan

Rutile

Titanite

(ten

analyses)

Biotite

eight

nalyses)

t207

Oxides

(wt%)

1E-RU7

Range Range

sio,

Al,o3

Tio,

FerO.*

FeO'

Mn O

Mgo

CaO

KrO

Totalt'

Si

rrtAl

retAl

Ti

Fep-

F#*

Mn

Mg

Ca

K

Total

0.88

0.00

98.92

0-20

0.00

0.00

0.00

0.00

0.00

100.00

0.01

0.00

0-00

0.99


4/13

I 208

SHAU

ET AL.:

ORIENTED

INCLUSIONS

IN BIOTITE

Trele 2.

Electronmicroprobe

nalyses f biotite,

muscovite, hlorite,

nd itanite

rom

Tananao rthogneiss,

ortheast

aiwan

Biotite

(27

analyses)

Muscovite

Titanite-

Oxides and elements

(wto/o)

Range

Ave.

Mu19

sio,

Alro3

Tio,

Cr,O3

FeO(Fe,O3)-'

MnO

Mg o

Ca O

BaO

Naro

Kr O

F

cl

Total

Si

r4tAl

relAl

Ti

FeF(Fe3*)*

Mn

Mg

16r>

Ca

Ba

Na

K

> cations

F

cl

35.03J5.56

1

.13-17.14

1.71J.83

0.00-o.04

20.80-22.57

0.20-0.36

7.65-8.64

0.00-0.1

0.06-0.32

0.05-0.1

9.33-9.65

0.03-0.30

0.00-0.05

5.479-5.545

2.521-2.455

0.431-0.694

0.208-0.446

0.000-0.005

2.712-2.936

0.026-0.047

1.771-2.016

0.000-0.017

0.004-0.020

0.015-0.036

't.851-1.927

0.01

-0.1 5

0.000-0.012

5.505

2.495

0.528

0.339

0.001

2.862

0.038

1.904

5.672

0.005

0 .010

0.023

1.888

15.598

0.067

0.005

14.007

0.000

0.005

0.007

0.016

20.025

0.061

0.006

30.69

2.26

36.39

0.00

0.54

o.21

0.00

28.77

0.14

0.03

o.o2

0.57

0.00

99.62

1.000

0.000

0.087

0.892

0.000

0.013

0.006

0.000

0.998

1.004

0.002

0.002

0.001

3.007

0.059

0.000

30.56

1.00

38.20

0.00

0.43

0.05

0.00

28.48

0.02

0.00

0.01

0.25

0.02

99.02

1.000

0.000

0.039

0.940

0.000

0.011

0.001

0.000

0.991

0.999

Al

:0 .042,Ti

:0 .014,Cr:0.0003,Fe:0.092,Mn:0.007,M9

:0 .0 3 8 ,

Ca :0 .0 0 0 8 ,

Ba :0 .0 0 1 , Na :0 .0 0 4 ,

K :0 .0 4 5 , F : O .O 2 7 ,l

0 .0 0 2 .

.

|

:

intergranular,R

:

replacing

lmenite nclusions n

biotite.

"

Total Fe

as

FeO tor

biotite,

muscovite,and chlorite, and as

FerO3 or titanite.

sumed to be 95.00/o or biotite, 99.00/o

or

titanite,

and

100.00/oor

rutile

(e.g.,

Shau

et al.,

l99l). Hole-count

spectraamount to only 0.50/o f the total counts

or

biotite

spectra

-60000

counts

for

each analysis)acquired

from

thin edges.

Nevertheless,

such

stray radiation contributes

up

to 300/o f intensities

for

elements

considered minor

in titanite and rutile

(e.g.,

K

and

Fe

of titanite).

Therefore,

analytical

data for titanite and rutile

were

corrected

by

subtracting

hole-count spectra.

For

biotite,

the

contri-

bution

of the

hole-count

spectrum

was negligible.

Rutile

Major

Ti

and O and

minor

Si

and Fe were detected

with

AEM

analysesof

needles orming the asterisks

Ta-

ble

1).

The

electron diffraction

patterns

from these hree

sets of

needleswere indexed

using the

cell

parameters

of

rutile

(a

:

4.59,

c

:2.96

A;. ttrese data,

n

combination

with the optical

properties

(very

high relief,

parallel

ex-

tinction, and

length

slow), show

that those

needles

onsist

of

rutile.

Figure 2 shows SAED

patterns

and a

TEM

bright

field

image obtained from a rutile

inclusion within

a biotite

flake that

was

oriented

with

(001) perpendicular

to the

electron beam.

The

electron beam

direction was thus ap-

proximately parallel

to c* of biotite.

It was

also

parallel

to a

(arbitrarily

defined

as

[010])

of

rutile.

The

SAED

pattern

in Figure 2a therefore

includes the

rutile

[010]

zone

pattern

and a slightly

misoriented

biotite

[001]

zone

pattern.

The

[001]

SAED

pattern

of biotite

is a

hexagonal

net that

includes

a*

and b*.

The

[010]

SAED

pattern

of

rutile exhibits h)l

reflections showing

elongation

or

streaking

along a*

(Fig.

2a). The

axes

c* and a* of rutile

are each

exactly

parallel

to

b* and a* of biotite,

respec-

tively,

when

projected

onto the

plane

ofthe

photograph.

The

[001]

axis of biotite

is

slightly

tilted toward

-a*,

as

is evident from the asymmetric intensity distribution of

biotite

reflections.

he

a axis

(instead

ofa*) ofbiotite

is

actually

nearly

parallel (+2)

to the

plane

of the

photo-

graph

when

the tilt

angle and

B

angle

ofbiotite are con-

sidered.

Therefore,

t is inferred that c*

of rutile is

parallel

to b* of

biotite

whereasa*

([00]*)

of

rutile

is

parallel

to

a of

biotite;

.e.,c*l lb"

and

(010)*l l(001)".

A

[010]

SAED

pattern

from another rutile

inclusion

shows

the following

features:an additional

set of

reflec-

tions occurring

as split

reflections along

a*, slight streak-

ing

ofreflections

along a*, and

superstructurelike

eflec-

tions that triple the

spacing

4,0,y

along

[01]*

or

[01]*

(Fig.

3a).

The additional set ofreflections

displays

a

per-

fect hexagonal-net

pattern

as

for biotite.

However, the

smallest

vectors

containing the

extra

reflectionsalong a*


5/13

SHAU

ET

AL.: ORIENTED INCLUSIONS

IN BIOTITE

r209

Fig.2.

(a)

SAED

pattern

ofthe

[001]

zoneofbiotite

(B) (slight-

ly misoriented)

and of the

[010]

zone

of a

rutile

needle

R).

The

b* axis ofbiotite coincides

with

c* ofrutile,

whereas

he

projec-

tion ofa*

ofbiotite coincides

with

a* ofrutile.

Difuse reflections

of

rutile

are elongated

parallel

to a*. The reflections abeled D

arecaused y double diffraction

(cf.

Hirsch et al.,1977).

(b)

SAED

pattern

with

a

smaller camera

length showing

reflections only

from the rutile

needle.The

reflectionscaused

by double diffrac-

tion are

not

present

since

there are

no reflections

rom biotite.

(c)

TEM bright

field image ofthe

rutile

needleelongated

parallel

to its c axis and

to b of biotite.

The

maximum

width of the

needle

is 0.15&m.

of

rutile correspond

o a d-valueof

2.52

+

0.04 A

(cali-

brated from rutile

cell

parameters),

which

can be

indexed

as the

ll0

reflection

of

hematite

(a:

5.034 A

and d,,,o,

:

2.517 A for

the hexagonal

ell) or

ilmenite

(a

:

5.088

A

and

d,,,0,

2.544

A1 wittrin

measurement

rror. These

reflections

are thus identified

as he

[001]

zone

pattern

of

hematite-ilmenitewith

(001)parallel

o

(010)

of rutile. A

dark field image

that

was formed

by using

the adjacent

200*

and

I 10"

reflections howswavy

stripesextending

parallel

to c

(Fig.

3b).

The

tetragonal symmetry

of rutile

implies

that

the

platelets

are also orientedwith

(001) parallel

o

(100)

of

rutile.

The wavy

stripes shown

in Figure

3b thus corre-

spond to such edge-on

platelets

and cause

he streaking

of reflections

along a* of rutile. These

edge-on

platelets

also contribute

to a

I

l0] zone

pattern

of

hematite-il-

menite, which

includes

a 006

reflection

d,oou

2.29 L

for hematite)

superimposedon the 200 reflection

of rutile

and thereforecontributes

o the

white

contrast

ofthe

wavy

stripes in Figure

3b.

The

superstructurelike reflections

along ( l0 I )* can be derived from dynamic diffraction (or

double diffraction,

cf.

Hirsch

eL al.,

1977)

of the

[10]

zone reflections f

hematite-ilmeniteand

the

[010]

zone

reflections

of rutile.

Similar

platelet

microstructures

were

observed

in Fe-bearing

rutile in

metapelites

from Ver-

mont

(Banfield

and

Veblen,

l99l) and

in synthetic

non-

stoichiometric

utile

(e.9.,

Bursill et al.,

1984).

Figure 4 shows three

rutile

needles ntersecting at a

triple

junction,

with an angle of

120" betweeneach

pair.

As

the

prism

axes of rutile

needles

were

observed

with

an optical

microscope o

lie in the

(001) plane

of biotite,

the collective

TEM

and

optical data suggest

hat the

rutile

inclusions

and

biotite

matrix have the

following crystal-

lographic relationship:

for

one

of the three

sets of rutile

needles, of rutile

(the prism

direction)

is

parallel

to

b of

biotite,

whereas

ar

and a2 of rutile coincide

with

a

and c*

of biotite,

respectively.

n other

words,

(010)

of rutile

is

parallel

o

(001)

of biotite.

The

c axes

of the other

two

setsof rutile

needlesare oriented

120"

(or

60') clockwise

and counterclockwise

rom

the

b axis of

biotite

in

(001)

of biotite.

Their

(010)

planes

are also

parallel

o

(001)

of

biotite.

Although

almost

all rutile

needles

were oriented

as described above, one exceptionhas beenobserved n

which

(l

l0) of rutile

was

parallel

o

(001)

of biotite.


6/13

t210 SHAU ET AL.: ORIENTED NCLUSIONS

N BIOTITE

Fig.

3.

(a)

SAED

pattern

of

the

[010]

zone of rutile. Reflections are difuse

and there are extra

reflections

(indicated

by black

arrows; see

ext) arranged

parallel

to a*.

The reflection

006n,superimposes n

the reflection

200". Superperiodic

eflections ripling

d,o, ie

along

[01]*

or

[0T]*.

R

:

rutile, H

:

plareletsll(010)R,

'

:

plateletsll(100)R.b)

A TEM dark

field image ormed

from

the reflections ncluding 200R,

006H,,and

I 10". The wavy

stripes

(indicated

by black arrows)

extending along c are

representative

ofthe edge-on

plateletsparallel

to

(100)*.

Fig. 4. TEM

bright

field image

of three

rutile

(R)

needles

intersecting at a triple

junction

and

partly

embedded n biotite

(B).

A fourth needle s located

at a

level

below the

three inter-

sectingneedles.

Titanite

The electron diffraction

patterns

of the

needlelike n-

clusions

orming equilateral riangles

can be

ndexed

with

the cell

parameters

of synthetic

titanite

(a

:

7

07, b

:

8 .72 , : 6 .57

A,

b :113 .86 ' ,

Speer

ndG ibbs ,

976 )

for space

gtoup

A2/a.

The AEM analyses

or these

nee-

dles

reveal the

presence

of

major Si, Ca,

Ti,

and

O with

minor

Al, Fe, and K

(Table

l).

These

data

collectively

show

that the

needlelike inclusions

that are elongated

parallel

to a ofbiotite

and oriented

as equilateral

riangles

are titanite.

Figure 5 showsa TEM image and a SAED

pattern

with

[01]

of titanite

and

(001)

of biotite

parallel

o the elec-

tron beam,

for which the specific

zone

of biotite

is

not

identified.

The

axis

I

lT]* of titanite

is

parallel

to

c* of

biotite,

indicating that

(l

I l)

oftitanite

is

parallel

or near-

ly

parallel

o

(001)

of biotite.

A

[213]

SAED

pattern not

shown

here) of the same

titanite

inclusion also

gave

a

diffraction

pattern

with

I

tT]x oftitanite

parallel

to c* of

biotite and therefore

onfirmed hat

(l1T)rll(001)"

or

that

titanite crystal.

Weak

and diffuse

streaks

parallel

to b* of

titanite

can be observed

n the

SAED

pattern (Fig.

5a).

Figure 6 is a SAED

pattern

of titanite

I

I l] and slightly

misoriented biotite

[001]

zones. Comparison

of the dif-

fraction pattern with the correspondingmageshows hat

the

prismatic

titanite

crystal

is elongated

parallel

to a* of


7/13

SHAU ET

AL.: ORIENTED INCLUSIONS

IN BIOTITE

L2rr

Fig.

5.

(a)

SAED

pattern

of the

[l01]

zone

of titanite

(T)

and

of biotite

(B)

where c* of biot ite

is

parallel

to

[111]*

of titanite;

i.e.,

(l

11)

oftitanite is

parallel

to

(001)

ofbiotite. There

are weak and diffuse streaks

parallel

to b* oftitanite.

(b)

Brieht field image

showing

that the interface

(indicated

by arrows) between

he titanite needleand biotite

host is

parallel

to

(001)

ofbiotite.

biotite. However,

the

difference n intensity

between

bi-

otite r00

and h00

reflections

suggestshat

the

[001]

axis

was tilted toward -a*, and a is inferred to be the axis

that is

actually

parallel

to the

prism

axis oftitanite when

the

tilt angleand

B

angle

ofbiotite

are aken nto

account.

It is

thus consistentwith

the

optical observation

hat

prism

axes

of titanite

are

parallel

to

(001)

of biotite. The

prism

axis

oftitanite is

perpendicular

o

[2T ]*;

i.e., t is

parallel

to

(21l).

Other diffraction

patterns

not

shown),consist-

ing

of

the biotite

[001]

zone

and

(l)

titanite

[2lT]

zone

and

(2)

titanite

[4ll]

zone,

show that the

prism

axes

of

titanite

are

parallel

o

(1Tl)

and

(0Tl)

of titanire, espec-

tively,

and are also

parallel

to a ofbiotite. Therefore,

he

prism

axis

of titanite

was

parallel

to the zone

axis

of

(21

),

(l

I l), and

(01

), i .e., o [0] l] of t i tanire.

Orientations

of

planes

and axes

of titanite

and biotite

as

determined by

diffraction

relations

were

plotted

on a

stereographic

projection

to characterize

heir relations.

The results,

based on

the

reflections

in Figure

6,

show

that the

prism

axis and

[0

I I

]

of titanite,

and a of biotite

are

parallel

o each

other

(+0.5')

when

projected

on

(001)

ofbiotite. They

also show

that

(l

lT)

oftitanite is nearly

parallel

to

(001)

of

biotite,

with

an interfacial

angle

of

2.2. The

direction

of the slow

and

fast

rays

of titanite

can

be determined from

the orientation

of the

crystallo-

graphic

axesoftitanite,

and thus the

extinction

anglecan

be

predicted.

The

extinction

angle

as

predicted

for

the

above relationship (Fig. 6) in which (001) of biotite is

normal

to the optical

axis is 22

+

2.

It is measured

clockwise

rom

the

fast-ray direction to the

prism

axis of

titanite.

However, because he titanite

prisms

of

any one

parallel set can be elongatedparallel to either [0ll] or

[0Tl]

(symmetrically

equivalent),

both clockwise and

counterclockwise extinction angles

should be observed

for

any one set.

The observation of such symmetrically

re-

lated extinctions

(see

above)

verifies the

orientation

re-

lation and shows that

it is

the

general

relation for most

needlelike

itanite.

A SAED

pattern

corresponding

o

[0]

l] of titanite and

[00]

of biotite,

as obtained rom a titanite

needle

parallel

to the beam, shows hat

[0ll]

of

titanite is

parallel

o a

of biotite

(Fig.

7). However,

(001)

of biotite

is

parallel

to

(433)

rather than

(l

lT) of titanite, and c* of biotite and

I l l]* of titanite are inclined by approximately 10", in

contrast to the above

relation in Figures

5 and 6.

A

[313]

SAED

pattern

of titanite

(not

shown), or

which

the beam

was

parallel

to

(001)

of biotite, also

ndicates

hat

(433)rll

(001)".

In

other electron diffraction

patterns, (001)

ofbiotite

was

ound to be

parallel

o nearly

parallel

o

(001),

101),

(0lT),

or

(410)

of titanite.

Assuming

that the

prism

axes

of such titanite needlesare also

parallel

to a of biotite,

stereographic

projections

show that they

must have

ex-

tinction anglesdifferent from thoseusually observed

l

8-

25')

for the titanite needles orming equilateral triangles.

Titanite

inclusions

with

such orientations are rare

rela-

tive to thosecommonly occurringorientationswith (11l)r

or

(433),l l(001)"

nd

[0]

l]rl l l l00lB.

(b)


8/13

t 2 1 2

SHAU ET AL.:

ORIENTED INCLUSIONS

IN BIOTITE

(c)

Fig.6.

(a)

SAED

pattern

of the

[1ll

zone

of

titanite. The

arrow is

parallel

o

[211]*.

(b)

SAED

pattern

ofthe

[001]

zone

of biotite

([001]

was

slightly tilted toward

-a*).

(c)

The

corre-

sponding bright field image shows hat the prism axis of titanite

(T)

is

perpendicular

o

[2

I

]*

of titanite

and

parallel

to the

pro-

iection

of a* of

biotite.

Fig.7 SAED

pattern

f the

0

I

]

zoneof titanite

T)

and he

u00l

zone

of biotite

B)

obtained

rom

a sample

with

the

prism

axisof titanite

parallel

o

the

electron eam.The axis I1]* of

this titanite

needle

s not

parallel

o c* ofbiotite.

Er,ncrnoN MrcRopRoBE ANALvsES

(EMPA)

Compositions of biotite, muscovite, chlorite, inter-

granular titanite, and titanite replacing ilmenite inclu-

sions

in

biotite

were

obtained

with

a Cameca Camebax

electron

microprobe

using

l2 kV

accelerating

oltage

and

l0 nA

beam current

(Table

2). The

standards

nclude

diopside

Si,Ca),

ndalusite

Al), geikielite Ti),

uvarovite

(Cr),

ferrosilite

(Fe),

rhodonite

(Mn),

olivine

(Mg),

san-

bornite

(Ba),

albite

(Na), potassium

feldspar

(K),

F-rich

topaz

(F),

and

barium chlorine apatite

(Cl).

The

beam

was astered veran area6

pm x

6

pm

forboth

standards

and specimens o

reduce oss

of alkali cations

resulting

from

diffusion.

The

composition

of biotite obtained

with EMPA is

consistentwith that obtained with AEM, except hat val-

ues

for minor elements are

better defined with EMPA.

The rangeand average

values

or 27 microprobe

analyses

of biotite and the

resulting compositions are

isted in Ta-

ble 2. Biotite that

has

been

overgrown or

partially

re-

placed

by chlorite

generally

contains

essTiOr. Muscovite

contains

essTiO, and

more NarO, whereaschlorite con-

tains much

lessTiO, but more MnO than biotite.

Structural

formulae of titanite

were normalized

to

I

Si,

as consistent

with occupancyofthe

tetrahedral site only

by

Si

and

assignmentof all

Ti, Fe3*,and

Al

to the octa-

hedral

site

(e.g.,

Higgins and

Ribbe, 1976).The coarser

grained

itanite,

which

either

replaces

lmenite inclusions

(in

biotite) or occurs

at intergranular

sites,

gives rise

to

titanite structural

formulae approaching

deal

values

(Ta-

[001]s


9/13

ble 2). The

titanite also contains

0.25-0.79

wto/o

f F.

However,

the titanite replacing ilmenite

contains much

less

AlrO. and F

but slightly more TiOr. When

compared

with

the acicular

itanite inclusions n biotite,

the coarser-

grained

titanite

exhibits

lower FerO,

and KrO

contents

and slightly higher

CaO content.

DrscussroN

Mineral

chernistry and microstructures

of

rutile

and titanite

Optical microscopy,

AEM microanalysis,

and electron

diffraction

have

shown that the needlelike

inclusions

forming

the asterisks

are rutile and those forming

the

equilateral

triangles n

projection

on

(001)

ofbiotite are

titanite. The

optical observations

and electron diffraction

data show

that the rutile

and titanite inclusions

generally,

but

not

always, have

a

preferred

orientation in

biotite.

The rutile

inclusions

contain minor

amounts of Si

and

Fe but no detectableTa5* or Nb5* that may be coupled

with

substitution

of

Fe3*

or

Fe2*,

as

observed by others

for rutile

(cf.

analysescompiled in Deer

et al., 1962b,

Rumble,

1976).As

described bove, he

SAED

patterns

ofrutile

exhibit features

ofstreaking,

reflections

rom

an

extra

phase,

and superstructurelike eflections.

The

streaking

of

reflections

along a*

of

rutile in

SAED

pat-

terns

(Figs.

2 and3) implies

the

presence

f

platelet

struc-

tures

parallel

to

(100)

of rutile, as directly seen n

dark

field images

Fig.

3b). The reflections rom

these

platelets,

though most

are superimposedon the reflections

of rutile,

can be indexed

as hematite-ilmenite

with

(001)rll(100)*.

The superstructurelike eflectionscan also be attributed

to dynamic

diffraction from

these

platelets

and rutile.

Furthermore,

the

additional set of

reflections

(Fig.

3a)

is

consistent

with

the

[001]

zone

pattern

of hematite-ilmen-

ite

that is

oriented

with

[T20]Hllc*

i.e.,

a..n

I

c.) and

(001)H

l(010)R.

Similar

streaking and splitting

of

reflections,

super-

structurelike reflections,

and

platelet

structureswere

ob-

servedby Banfield

and

Veblen

(

I

99

)

in

Fe-bearing utile

(FeO

:

0.5-3

wto/o)

rom chlorite-

to staurolite-grade

metapelites.They

have concluded that

coherently nter-

grown

hematite

(or

ilmenite)

platelets precipitated

par-

allel to

(100)

and

(010)

of rutile and that the streaking f

reflections

s due to

platelets

of irregular

spacing,whereas

the superstructurelike

eflections

are

causedby dynamic

difraction.

Putnis

and

Wilson

(1978)

and

Putnis

(1978)

noted

that experimental annealing of natural Fe-bearing

rutile

(FeO

:

0.55

wto/o)

t

temperaturesbetween47

5 and

595'C

resulted n

precipitation

of two

transitional

phases

(coherent

Fe-rich

precipitates)

and hematite. Bursill

et al.

(

I

984) observed

{

I

00}

platelet

defects,often occurring n

association with

crystallographic shear

planes,

in

syn-

thetic

nonstoichiometric

utile

(TiOr_",

0

=

x

<

0.0035).

They

srrggestedhat the

platelet

defects

precipitated

as

a

TirO,

phase

with

the corundum-type

structure and

that

the microstructuresare strongly determined by cooling

history. The

{

100}

platelet

defects hat

they observed

have

r213

0 .0

F

Fig.

8.

Plot

of

Al + Fe + Mn vs.F n ion numbers

er

ormula

unit for titanite rom the Tananao rthogneissopensymbols),

including ntergranularitanite

circles)

nd itanite eplacing

l-

menitenclusionsn biotite

triangles).

he

positive

rend s more

obvious

when

he analyses f titanite

compiled y

Higgins

and

Ribbe

1976)

realso

plotted

solid

squares).

zigzag changes

n

orientation

and are similar to the

wavy

stripesdescribedabove.

Putnis

(1978)

and

Bursill

et

al .

(1984) proposed

different

structural

models for the

pre-

cipitated

phases

o

interpret

the

superstructurelike

eflec-

tions tripling d,o,of rutile

(see

Banfieldand

Veblen, 99l

for review).Miser and Buseck 1988)observedpolysyn-

thetic

twinning

on

{100}

of rutile

and other defectstruc-

tures

in

O-deficient

rutile that occur

in mudstone xeno-

liths from

an

environment

with low

/o'

As evidencedby

the SAED

patterns

and

TEM images

(Figs.

2

and 3), the

rutile

inclusions n

the

sageniticbiotite

from

the

Tananao

orthogneisscontain

precipitated

{

100}

platelets

hat have

the

hematite structure.

However,

these

platelets

are ikely

to have Ti substituting

for Fe, as mplied by the

low

con-

tents of

FerOr(-0.2

wtolo)

n

rutile

and the abundanceof

platelets (Fig.

3b).

The titanite inclusions always contain minor

amounts

of Al, Fe,and K in addition to the major elementsSi, Ti,

and Ca, even after subtraction of

hole

counts

(Table

l).

The composition of titanite is

generally

afected by sub-

stitutions such

as

(Al,Fe)3*

+

(F,OH)-

:

Ti4+ +

6:-

lHig-

gins

and Ribbe, 1976; Deer et al.,

1982).Although

F and

OH could

not

be detectedby

AEM for the

titanite

inclu-

sions, microprobe

analysesof

the coarser

grained

titanite

indicated that F contents have a

positive

correlation

with

those of

Al + Fe

(Fig.

8).

The

substitution

of Al

and

Fe for Ti and of OH. Cl.

and

F for

O in natural titanite

favors

the

formation

of

domains between

which

the directions of

Ti

displacement

in TiOu-octahedra reverse from +a

or

-a

(Speer

and

Gibbs, 19761-Taylornd Brown, 1976).Synthetic itanite

undergoesa

reversible,

displacive

phase

ransition at

220

SHAU ET AL.: ORIENTED INCLUSIONS

IN BIOTITE

0.3

+

f r

+

e

0.1

0.3

.2. 1


10/13

tzt4

SHAU

ET

AL.:

ORIENTED

INCLUSIONS

IN BIOTITE

oo

+

.g)

(.)

f Y

0.60

0.55

0.50

0 . 1

0.2 0 .3

Ti

Fig.

9.

Plot

of

Fe/(Fe

+ Mg) vs. Ti

per

ormula

unit

(22

O)

for sageniticiotite rom theTananao rthogneiss.nalysesb-

tainedwith AEM

(solid

circles) nd

EMPA

(open

circles), e-

spectively.

+

20

"C

from

space

group

P2,/a

to A2/a

(Taylor

and

Brown, 1976).

Higgins

and Ribbe

(1976)

demonstrated

with X-ray

diffraction

and electron diffraction data

that

the space

group

of

natural

titanite varies from P2,/a for

relatively

pure

end-member compositions

to

A2/a wth

increasing

substitution

of

Al

and

Fe. The

SAED

patterns

oftitanite inclusions

n

the sageniticbiotite

generally

ex-

hibit no reflections

with k +

/ odd, as consistent with

spacegroup A2/a, but some of them have faint diffuse

streaks

parallel

to

b*

(Fig.

5a) or c*

(not

shown). The

results further

demonstrate that

titanite

with

significant

Al

and Fe has

disorder in Ti displacements

as consistent

with

space

group

A2/a.

Chemical relations for

titanian biotite

Biotite

commonly has up to a few weight

percent

of

TiO,

(l-5

wto/o)

nd less

han

I

wo/o of CaO

(e.g.,

Foster,

1960a, 1960b;

Deer er

al.,

1962a).The Ti in

biotite is

located in

octahedrally coordinated

sites, and

its

substi-

tution

is

coupled with substitution

of

Al for

Si

(i.e.,

Ti-

Tschermak's

substitution: Tio* + 2,\lt*

:

Mg2r +

2Si4+'

e.g.,Robert, 1976;

Guidotti,

1984;

Hewitt

and

Wones,

1984),

ubstitution

of O

for

OH

(e.g.,

Bohlen

et al., 1980),

or octahedral

vacancies

(e.g.,

Dymek, 1983

and refer-

ences herein). Therefore,

titanian biotite

may

consist of

one or more

of the componentsKr(Mg,Fe)5TiSi4Al4Oro

(OH)",Kr(Mg,Fe)rTiSiuAlrOrr(OH)r,

r

K,(Mg,Fe)oTiSi6Al,

Oro(OH)o.The

biotite

in

the

Tananao

orthogneiss

con-

tains I .5-3.8 wto/o iO,

(Tables

and 2). The

Ca contents

were near

limits

of detection by AEM and microprobe

analyses

CaO

:


11/13

SHAUET AL.:ORIENTED NCLUSIONS

N BIOTITE

L2I5

conditionsofthe

greenschist

acies

T:350-475

"C

and

P

:

5

kbar)

(Chen

et al., 1983). The

orthogneisswas

derived from

the

granitic

intrusions

following

the second

amphibolite facies metamorphism.

The

entire sequence

of metamorphic rocks,

consistingof schists,

amphibolites,

serpentinites, marbles, metabasites,

and

gneisses,

was

known

as he

Tananao

schists

n

the

past

but as he

Tana-

nao complex in recentyears.

Yang

and

Wang

Lee

(

198

)

found

that titanite is

a com-

mon

accessory

mineral in

the

gneisses

nd

other

meta-

morphic

rocks

of the Tananao

complex and

that titanite

has wholly

or

partially

replaced

ilmenite

in the

ortho-

gneisses

and

amphibolites

derived from

basic igneous

rocks.

They

thus concluded

that titanite was

stable

and

should have

crystallized f Ti,

Ca, and Si were

available

under

the metamorphic

conditions for

the Tananao

com-

plex.

Rutile

was

also shown

to be stable n

the tempera-

ture

and

pressure

anges

of the metamorphism

(cf.

Jam-

ieson

and

Olinger, 1969).

Preferred orientation occurring in two intimately co-

existing

phases

s commonly

a

result

of exsolution

or to-

potaxial

(topotactic)

or epitaxial intergrowth.

However,

exsolution equires

hat the

reactant

componentsareequal

to those of the

sum of the

products;

simple exsolution of

titanite

and rutile is

therefore

precluded,

as the addition

of rutile and

titanite components

o the biotite leads

o a

nonsensible

ormula for

the hypothetical

precursor.

The

process

must

therefore nvolve

addition

or

loss

of one or

more

components.BecauseTi

and Ca are common

com-

ponents

of biotite

and because utile and

titanite are

ran-

domly

distributed throughout

biotite, the source

of the

Ti

and Ca of titanite and rutile was most likely as a solid

solution component

of the biotite. These elations

collec-

tively

require

dissolution

and

recrystallization

of at

least

a

portion

of the original biotite, with

gain

or loss

of com-

ponents.

As

discussedabove, the solubilities

of Ti and Ca in

biotite

generally

ncreasewith

increasing

emperature.

f

biotite of an igneous origin was metamorphosed

under

the amphibolite or

greenschist

acies

conditions deter-

mined for

the

Tananao

complex, high Ti

and Ca com-

ponents

inherited from higher

temperature

conditions

could

well

be

in

excessof the

limits

allowed at

lower

temperatures.Reactions nvolving

the breakdown

of the

Ti-

and Ca-rich biotite to Ti- and

Ca-depletedbiotite

plus

titanite, rutile,

and other

phases

might

thus take

place

during

metamorphism

when biotite with

high Ti and

Ca

contents

was no longer

stable. Studies

of

hydrothermal

experimentsalso

showed hat

Ti-rich

phlogopite

forming

at

higher

temperatures

=

1000

C)

breaksdown

to assem-

blagesof Ti-depleted

phlogopite,

rutile, and sanidine or

vapor

at

lower

temperatures

s800

"C)

(Forbes

and

Flow-

er,1974;Tronnes

et al., 1985).They

alsoshowed

hat the

Ti content

of

phlogopite

increases

with increasing

em-

perature

and

decreasing

pressure

or

a

given

bulk TiO,

content.

Alternatively, titanite andrutile could have ormed con-

comitantly with

the topotaxial

breakdown of biotite

to

chlorite

(cf.

Veblen

and Ferry, 1983; Eggleton

and Ban-

field, 1985)

during

an early

retrogressive

pisode

fpoly-

metamorphism.

Titanite

or

rutile formed in this manner

would likely be observed as

well-oriented acicular inclu-

sions

in

chlorite,

as

reported

by

Rim5aite

(1964),

al-

though

titanite usually occurs as

relatively large crystals

without

preferred

orientation

in chlorite

(Dodge,

1973;

Ferry,1979 Parry and Downey,

1982;

Veblen

and

Ferry,

1983). Baxter and Peacor (unpublished data) observed

both

titanite

and rutile

intergrown with interlayeredchlo-

rite and

biotite

in samplesof altered

ufaceous

rocks rom

New Z.ealand,

where

the chlorite

was

an alteration

prod-

uct of

Ti-rich

detrital

biotite.

Ferry

(1979)

suggested

reaction that accounts

or

the

formation of chlorite

and

titanite from

Ti-bearing

biotite

by

hydrothermal alter-

ation

in

granitic

rocks. The chlorite thus

formed

in

an

early stage of

retrograde metamorphism

might

have

transformed topotaxially

to biotite and

retained

well-ori-

ented titanite and

rutile

in

biotite

during a

final

progres-

sive episode of the

polymetamorphism,

which occurred

at the conditions well above the biotite isogradaccording

to several

prograde

eactions

e.g.,

Ernst,

1963; Brown,

r97 ).

However, since a sagenitic

biotite

with

well-oriented

inclusions of titanite

and rutile

may also be altered to

chlorite and

retain the

preexisting

nclusions

in

chlorite,

existenceof sagenitic

chlorite does

not necessarily mply

that the titanite

and rutile

inclusions

formed during al-

teration

of biotite to

chlorite.

In

addition,

titanite,

which

has been characterized

as one ofthe

products

during al-

teration ofbiotite to chlorite,

does

not

generally

occur as

well-oriented, needlelike

nclusions ike those

n

this study

(Dodge, 1973; Ferry, 1919; Parry and Downey, 1982;-

Veblen and

Ferry, 1983).Therefore,

t is more

likely

that


formed by a

precipitation

mechanism

where

titanite,

rutile, and

Ti-depleted biotite crystallized

topotaxially during

metamorphism through the

break-

down of a

Ti-

(and

Ca-)

rich biotite that

had formed under

conditions

of

higher temperatures

(e.g.,

gneous biotite)

than those of the

metamorphism.

Chlorite observed

n

the

present

nvestigation,

which is

presumed

o

replace

biotite

or overgrow biotite

during the

latest

greenschist

aciesmetamorphism, does

not contain

well-oriented acicular

nclusions.

t

apparently

has no re-

lationship

with

the

formation of acicular

inclusions

in

biotite.

In

addition,

the

rutile inclusions

n

biotite contain

precipitated

hematite-ilmenite

platelets

hat

should

post-

date he

formation of rutile

(cf.

Banfieldand

Veblen, 199

).

Precipitation

of

hematite

in rutile took

place

within

an

approximate

temperature

angeof

450-600

"C,

according

to observationsof experimentally

annealed

utile

(Putnis,

1978;Putnis

and

Wilson,

1978), hough he

precipitation

temperatures

are

probably

lower, based on

the observa-

tions by Banfield and

Veblen

(1991)

and

Bursill

et al.

(1984).

Therefore,

precipitation

of

rutile

and

titanite in


probably

took

place

during

the am-

phibolite

facies

metamorphism or

following

retrograde

metamorphism at temperatureshigher than those of the

latest

greenschist

acies metamorphism

for

the

Tananao

complex. Other examples

of

precipitated

nclusions, such


12/13

t 2 t 6

as well-oriented magnetite nclusions n

pyroxenes Fleet

et al., 1980)and hematite nclusions n sillimanite

(Fleet

and

Arima, 1985),

have been

reported

as occurring

n

metamorphic rocks with

a complex

retrogradehistory.

Structural control of the

well-oriented nclusions

in biotite

Optical and TEM

observationsshowed

hat one

of the

three sets

of

intersecting

rutile

needles orming

asterisks

is

parallel

to b

of biotite.

The

prism

axesof rutile

needle

are

parallel

o c, and

(100)

or

(010)

of rutile are

parallel

to

(001)

of biotite. The rutile structure s

composed

of

parallel

chains ofedge-sharingTiOu octahedra

hat

extend

parallel

o c

and are connected

aterally

by sharing

vertices.

The

O

layer, which

is

parallel

o

(

100)or

(0

10)

of

rutile,

is nearly

closest-packed, hough slightly

puckered.

The

biotite structure s

also basedon closest

packing

ofanions,

with

anion layers

being

parallel

to

(001)

of biotite.

(Draw-

ings

of the rutile

and biotite structures can be

found in

many standard textbooks

of

mineralogy

and

will not

be

given

here.)Preferred

orientation involving

(

I 00) or

(0

I 0)

of rutile and

(001)

of biotite

is

therefore understandable

in

terms of their similar closest-packed

eometries.

Fur-

thermore, he

(Mg,Fe,Al,Ti)(O,OH)u

ctahedra fthe bru-

cite-like octahedral sheet of biotite form chains of octa-

hedra

by sharing edges,as in rutile. Such chains extend

in three directions,

each oriented 60"

from

the others and

conforming o the

pseudohexagonal

ymmetryof

(001)

of

biotite. During

dissolution

(of

biotite) and crystallization

(of

rutile),

migration

of

Ti into

those octahedra

n

sub-

stitution of

Mg,

Al, and

Fe

and replacementof OH by O

could easily convert the edge-sharing (Mg,Fe,Al,Ti)-

(O,OH)6

octahedra nto

chains of edge-sharing

TiOu

oc-

tahedra

o

form

a

pattern

ofthree rutile needleswith ends

intersecting

at angles of

120"

(Fig.

a).

Superposition of

another

pattern

that

consists

of

three

needles

extending

in

the directions opposite to those of the first

pattern

createsan asterisk

pattern

with

adjacent

needles

at angles

of 60'

(Figs.

I and 4). Growth of

rutile

needles

hus

in-

volves minimum reconstruction

and cation diffusion.

Fleet and Arima

(1985)

studiedoriented

hematite n-

clusions

n

sillimanite and

indicated

that

(120)

of

he-

matite is

parallel

to c of sillimanite,

which is

the

direction

containing chains of edge-sharing octahedra for both

phases.

The

orientation

relationships

of

magnetite nclu-

s ions

in

pyroxenes,

nc luding

{

I I I

}Ml l

100}"

and

(

I I

2

),

ll

c", are also related o closest-packed

O

layersand

chains of edge-sharing ctahedra

(Fleet

et al., 1980).

Platelets

of

hematite

or

(Fe,Ti)rO,

nclusions n

rutile

with

{001}Hll{100}.

nd

(120)"l lc.

have

beenobserved

n the

present

nd other studies

Putnis

and

Wilson, 1978;Put-

nis, 1978;

Bursill

el al.,

1984;Banfield

and

Veblen, 1991).

Gilkes and Suddhiprakarn

(1979)

reported

a

preferred

orientation between

goethite

and

biotite

with

{100}cll 001}u

and collbu

n

deeply

weathered

ranitic

rocks, although

other orientations between

goethite

and

biotite

have

been

observed by

Banfield

and

Eggleton

(1988).

All these

preferred

crystallographic

elations

be-

SHAU ET AL.: ORIENTED

INCLUSIONS

IN BIOTITE

tween

rutile and biotite,

magnetite

and

pyroxenes,

utile

and

hematite, and

goethite

and

biotite

have a common

structural

similarity,

in

that

the two coexisting

phases

share

nearly closest-packed

anion

layers and chains

of

edge-sharing

octahedra

within the anion

layers

and

are

thus topotaxially

controlled

(cf.

Fleet,

1982; Fleet and

Arima. 1985).

Although

most titanite

inclusions

exhibit

prefened

ori-

entation

in biotite,

TEM data

have shown

that

many dif-

ferent

orientations

with

respect to

(001)

of biotite

also

occur.

It

is

estimated

that

more than

800/o f the

titanite

inclusions are elongated

parallel

to

(0

I I

)

and to

the three

directions

orming equilateral

riangles,

with

{

l l

}

or

{43

3

of

titaniteapproximately

arallel

o

{001

ofbiotite.

How-

ever,

n

contrast

o the

single

kind oforientation

occurring

almost

exclusively

for

rutile, other orientations

in which

{001}, {l0T},

{0lT},

or

{410}

of t i tanite

are

parallel

o

{001}

of biotite

were

also

observed.

An orientation

with

{

I

l0}

of titanite

parallel

o

{001}

of

mixed-layerbiotite-

chlorite in alteredgranitic biotite from southeasternAus-

tralia

was

observed

by

Eggletonand

Banfield

(1985).

The

variable orientations

of titanite

with respect o

{001}

of

biotite

indicate that titanite

does

not

have well-defined

structural

features n common

with biotite.

Nevertheless,

the

preferred

orientation

(0ll)'lla"

implies some struc-

tural control,

but

we have been unable

to define

one.

AcrNowr,nocMENTS

The

authors

are

grateful

o

Eric

J.

Essene,

amsin C. McCormick, and

J.

AlexanderSpeer

or critical

reviews

ofthe

manuscript.

We thank Pouyan

Shen

and Su-Cheng

Yu for many

helpful

discussions.

Transmission and

analltical electron microscopic work was carried out at the Institute of

Mining, Metallurgy

and Material Sciences

of the National Cheng

Kung

University

and the

Institute of Materials Science

nd Engineeringof the

National Sun

Yat-Sen University

in Taiwan,

Republic of China, and

in

the Electron

Microbeam Analysis

aboratory, the University of

Michigan,

Ann Arbor, Michigan.

A tit anite standard

B20360)

or AEM analyses

was

kindly

provided

by the

National Museum ofNatural

History, Smithsonian

Institution. The

present

study

was

supported

by the

grants

NSC-67M-

0202-

2(02\, NSC-75-M006-0202-03, and

NSC-76-M006-0202-02 to

H.-Y.Y. from the

National

Science

Council of the

government

of the

Republic of China, and by

NSF

grant

EAR-8817080 to D.R.P.

The

CM-

l2

STEM

was acquired under NSF

grant

EAR-8708276 and the electron

microprobe under

NSF

grant

EAR-8212764. Contribution

no. 476 from

the

Mineralogical l:boratory,

Department of Geological Sciences,Uni-

versity

of

Michigan, Ann Arbor, Michigan

48109,

U S.A.

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SHAU ET AL.:

ORIENTED INCLUSIONS

IN BIOTITE

on oriented titanite and rutile inclusions in sagenitic biotite

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