SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES • NUMBER 10

Mineralogy, Mineral-Chemistry, and

Composition of the

Murchison (C2) Meteorite

Louis H. Fuchs, Edward Olsen,

and Kenneth J. Jensen

SMITHSONIAN INSTITUTION PRESS

City of Washington

1973
ABSTRACT

Fuchs, Louis H., Edward Olsen, and Kenneth J. Jensen. Mineralogy, MineralChemistry, and Composition of the Murchison (C2) Meteorite. Smithsonian

Contributions to the Earth Sciences, number 10, 39 pages, 19 figures, frontispiece,

1973.—The Murchison meteorite shower, September 28, 1969, occurred in and

around Murchison, Victoria, Australia. Chemical and mineralogical analyses

established it as a type II carbonaceous chondrite (C2). Murchison consists

largely of fine-grained black matrix which has been identified as primarily a

mixture of two iron-rich, low-aluminum chamosite polytypes. Contained in the

matrix are four main types of inclusions: (1) single crystals and crystal fragments, (2) loosely aggregated clusters of crystals ("white inclusions"), (3) discrete

true chondrules, (4) xenolithic fragments of two other meteorite types (mostly

a unique kind of C3 chondrite).

The first type of inclusions consists of unzoned and highly zoned olivines,

unzoned (disordered and ordered) orthopyroxenes, clinoenstatite, and rare diopside. Prominent minor phases are calcite, chromite, metal (with occasional traces

of schreibersite), troilite, pentlandite, and two phases that could not be fully

characterized.

The second type of inclusions consists primarily of grains of olivine (Fa 0

to Fa 40), lesser low-Ca pyroxenes, and minor spinel, calcite, whewellite, hibonite, perovskite, chromite, pentlandite, and rare Ca-pyroxene.

The true chondrules consist of olivine, Ca-poor pyroxene, occasional metal,

and, in rare instances, one of the poorly characterized phases. The chondrules

are not texturally typical of the ordinary chondrites, but resemble more closely

those chondrules seen in C3 and C4 chondrites.

The fourth type of inclusion consists mainly of distinct xenolithic fragments

of a light blue-gray chondrite type that resembles certain C3 chondrites (like

Vigarano), though not in all aspects. These xenolithic fragments consist of disequilbrated olivines and pyroxenes, abundant pentlandite and troilite, and

virtually no metal. In addition, a single xenolithic fragment was found of an

unknown meteorite type.

Ca- and Al-rich glasses (of varying compositions) are found as blebs, with

or without gas bubbles, contained within olivine crystals. The average Ca/Al

ratio of these glasses approximates that for all meteoritic matter. They may

represent early (nonequilibrium) subcooled condensates from the solar nebula.

This nonequilibrium stage was apparently followed by equilibrium condensation

through intermediate to low temperatures at which the layer-lattice phases condensed in abundance and incorporated crystals and fragments of the higher

temperature phases.

OFFICIAL PUBLICATION DATE is handstamped in a limited number of initial copies and is recorded

in the Institution's annual report, Smithsonian Year. SI PRESS NUMBER 4784. SERIES COVER

DESIGN: Aerial view of Ulawun Volcano, New Britain.

Library of Congress Cataloging in Publication Data

Fuchs, Louis H.

Mineralogy, mineral-chemistry, and composition of the Murchison (C2) meteorite.

(Smithsonian contributions to the earth sciences, no. 10)

I. Meteorites. I. Olsen, Edward John, 1927—joint author. II. Jensen, Kenneth J., joint

author. III. Title. IV. Series: Smithsonian institution. Smithsonian contributions to the

earth sciences, no. 10.

QE1.S227 no. 10 [QE395] 550'.8s [523.5'1] 72-13427

For sale by the Superintendent of Documents, U.S. Government Prin'ing Office, Washington, D.C. 20402

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Contents

Page

Introduction 1

General Description 2

Mineralogy 3

Layer-Lattice Silicates 3

General Considerations 3

Compositional Evidence 4

X-ray Evidence 5

Other Layer-Lattice Silicate . 8

Olivine 9

Ca-Poor Pyroxene 9

Calcic-Pyroxene 9

Metal 9

Sulfides 10

Phosphorus Minerals 11

Calcite 11

Whewellite 11

Spinel Group Minerals . . 11

Lawrencite (?) 13

Hibonite (CaAl12O19) . 13

Perovskite 13

Sulfates . 13

Glasses 15

Poorly Characterized Phases 17

Textural Features . 19

Type 1 Inclusions . 19

Type 2 Inclusions 22

Type 3 Inclusions (True Chondrules) 23

Type 4 Inclusions (Xenolithic Fragments) 26

C3 Chondrite Inclusions 26

Xenolith of Unknown Meteorite Type 27

Mineralogical-Compositional Relationships 28

Calcium in Olivines . 28

Chromium in Olivines 28

Manganese in Olivines 28

Nickel in Olivines . 29

Nickel in Pyroxenes 30

Chromium and Phosphorus in Metal 30

Minerals Not Present in Murchison 30

Wet Chemical Analysis of Murchison . 31

Summary and Discussion of Observations 31

Appendix: Description of Wet Chemical Analytical Procedure 36

Literature Cited 37

i n
FRONTISPIECE: A fragmental grain of olivine removed from the matrix of the Murchison meteorite; its resemblance to an "organized element" is purely coincidental. The "eye" of our

friend is a calcium aluminum silicate glass inclusion (21 microns long), the "pupil" is a void

bubble. The presence of the bubble, the ovate shape ot the "eye" together with its composition,

all indicate that the inclusion formed from a liquid state at temperatures between 1250° and

1450°C.
Mineralogy, Mineral-Chemistry, and

Composition of the

Murchison (C2) Meteorite

Louis H. Fuchs, Edward Olsen,

and Kenneth J. Jensen

Introduction

The Murchison meteorite shower occurred on

September 28, 1969, 1045 hours local time, 85

miles north of Melbourne, Australia. Details of

the fall and an initial description are given by

Lovering et al. (1971). In addition, Clarke (personal communication) has assembled details

pertinent to the strewnfield. A chemical analysis

was reported by Jarosewich (1971) and a short

description was published by Ehmann et al. (1970).

A somewhat more detailed description was given

by Fuchs, Jensen, and Olsen (1970) before the

1970 meeting of the Meteoritical Society.

Murchison is the largest known fall of a type II

carbonaceous chondrite. The major portion, approximately 65 kg., is located at the Field Museum

of Natural History, Chicago. Other major portions

are located at the National Museum of Natural

History, Smithsonian Institution, Washington, D.C.

(approximately 30 kg), the Australian Museum,

Sydney (approximately 4 kg), and the University of

Melbourne (approximately 7 kg). In addition,

Louis H. Fuchs, Chemistry Division, and Kenneth J. Jensen,

Chemical Engineering Division, Argonne National Laboratory,

Argonne, Illinois 60439; Edward Olsen, Field Museum of

Natural History, Chicago, Illinois 60605 and Department of

Geological Sciences, University of Illinois-Chicago Circle,

Chicago, Illinois 60680.

smaller quantities, up to several kilograms, have

been acquired around the world by a number of

museums, universities, and private persons.

In making this study we were fortunate in having

such a large quantity of this meteorite available.

Several hundred hand specimens were examined

and seven polished microscope mounts were used.

Mineral identifications were made by optical examination of handpicked grains and confirmed by

X-ray powder diffraction in all instances.

ACKNOWLEDGMENTS.—We would like to thank

Dr. Milton Blander, Argonne National Laboratory,

for many stimulating discussions on some of the

features observed in the Murchison meteorite and

Dr. E. Roedder, U.S. Geological Survey, for his

penetrating comments on portions of the manuscript. We are grateful to members of the staff of

the National Museum of Natural History: Dr. Brian

Mason, Eugene Jarosewich, Joseph Nelen, Grover

Moreland, and Roy S. Clarke, Jr., for helpful counsel and for making available unpublished data

on Murchison. Dr. Warren Forbes and Mrs. Margaret Meyers, University of Illinois—Chicago Circle

Campus, helped in a portion of the microprobe

work and data reduction, and this is gratefully

acknowledged. We thank Mr. Karl Anderson, Argonne National Laboratory, for help on the microprobe at ANL, and Irene M. Fox (ANL) and

Ralph W. Bane (ANL) who obtained the carbon,
SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

hydrogen, and nitrogen data reported. We especially thank Mr. Francis (Bert) Eliason of Murchison, Australia, for making available the most

significant portion of the Murchison fall and pointing out features we might otherwise have missed,

and Mr. Glenn Commons and Mr. R. Groh who

provided the financial assistance to obtain the

major portion of this significant meteorite. Edward

Olsen was partly supported by a grant from the

National Aeronautics and Space Administration

(NGR-014-052-001), and Louis H. Fuchs was

partially supported by a NASA research grant. This

grant is gratefully acknowledged. Part of the work

was supported under the auspices of the United

States Atomic Energy Commission. The cost of

publication was paid by Argonne National Laboratory and the Field Museum of Natural History.

General Description

Murchison consists of numerous individuals ranging from a few grams to seven kilograms. Most

of the pieces are surrounded by fusion crust; however, because of low mechanical strength many are

broken and cracked, some possessing no crust at

all because it has spalled off at impact and afterward due to normal handling. Many specimens

show severe desiccation cracking, presumably due

to loss of volatiles. Several observers have noted

gradual weight changes, both losses and gains,

that are presumably due to changes in atmospheric

conditions in the several laboratories where weight

checks were made. Fine-grain size coupled with

good porosity and permeability permit the meteorite to "breathe." Although this has only modest

effects in the mineralogy, major composition, and

petrography, it can have serious implications for

any work that involves gases and organic chemistry.

In comparing hand specimens with other C2

chondrites Murchison shows a similarity only to

Murray. The ratio of inclusions + chondrules to

black matrix is clearly higher in both these meteorites (Figure 1) in contrast to others of this group,

such as Mighei, Cold Bokkeveld, etc. Typical of

IFICURE 1 Hand specimens (left to right) of Murchison, Murray, and Mighei C2 meteorites.

Murchison and Murray show a closely similar content of inclusions, in contrast to other C2s

such as Mighei. The Mighei specimen is 7 cm long.
NUMBER 10

C2s the matrix is deep black and featureless. Dispersed throughout the matrix are several distinct

types of inclusions: (1) single crystals and crystal

fragments of individual minerals ranging from a

few microns up to millimeter size; (2) multi-grained

mono- and polyminerallic inclusions up to 2mm,

which we will call white inclusions; (3) true chondrules that are spherical or fragmented spherical

segments ranging in size from 0.05 to 0.8 mm; and

(4) angular xenolithic fragments of another c-hondrite type that range from a few millimeters up

to 13 mm, which we will call xenolithic fragments.

In making the distinction between the type 2

and type 3 inclusions above, we have relied upon

clear textural characteristics: the white inclusions

(type 2) have a granular texture—the loosely held

mineral grains can be raked out easily with a

needle. They are of various shapes and break with

the fine-grained black matrix that surrounds them.

True chondrules (type 3), on the other hand, are

relatively hard, well-defined spherical objects—the

minerals cannot be scraped out with a needle. They

do not break with the matrix but detach as distinct

beads. Figure 2 illustrates the difference between

the white inclusions and the true chondrules. We

emphasize this distinction because casual observers have tended to refer to all the inclusions as

chondrules. In certain instances this distinction is

not clear-cut.

Of these four types, the first two comprise over

98% of the inclusions seen in the black matrix.

Each type will be described after the total mineralogy has been presented.

FIGURE 2.—Chondrule (0.9 mm in diameter) in matrix with

white inclusion next to it.

Mineralogy

LAYER-LATTICE SILICATES

The major mineral in Murchison is the black

matrix layer-lattice silicate. It comprises 77 vol. %

as determined by linear measurements across two

hand specimens. Whether this phase is truly black

cannot be determined; it may be that the color is

due to disseminated submicroscopic amorphous

carbon and organic compounds. In addition, finely

divided sulfides (such as troilite) are black. Our

microprobe results show a consistent matrix carbon content, 1.6-2.2 wt. %, and sulfur, from

1.6-4.1%.

Because the layer-lattice silicate is the major

phase in all C2 chondrites, its definite characterization is highly desirable, especially as it has implications for the genesis of this primitive group.

In spite of reported attempts by numerous investigators over the past twenty years, definite and

consistent results have not been obtained. The

only consensus is that it is a hydrated layer-lattice

silicate, either of the septechlorite group or serpentine group. Bostrom and Fredriksson (1966) presented microprobe and X-ray data suggesting it is

a ferric chamosite (septechlorite). Bass (1971) has

published a thorough review of the literature on

this matter.

GENERAL CONSIDERATIONS.—Because the matrix

phase comprises the dominant mineral making up

Murchison and because the other phases are notably iron-poor, the bulk of the iron oxide in the

whole meteorite analysis must be in the matrix

phase. Serpentines in general are most often ironpoor and magnesium-rich. In C2 meteorites it has

been believed that magnetite, submicroscopically

disseminated in a magnesian serpentine, could account for the bulk iron content. In Murchison,

however (and probably in other C2 meteorites),

magnetite is only a trace mineral (cf., "Spinel

Group Minerals"); the weak magnetic properties

of the matrix appear to be due to an Fe-S-O phase

(cf., "Poorly Characterized Phases").

On the other hand, the low total aluminum content of the meteorite argues against normal

septechlorites. The only known (terrestrial) septechlorites with low Al and high Fe are cronstedite

and greenalite. These, however, have too low magnesium to account for the bulk Mg content of the
SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

meteorite analysis. Frondel (1962) has reported on

the serpentine, ferroantigorite (formerly called

jenkinsite), a platy polytype or serpentine. On

compositional grounds it might be comparable to

the matrix material in Murchison.

COMPOSITIONAL EVIDENCE.—The H2O content of

the matrix can be estimated from that fraction of

the water content of the meteorite liberated above

105°C. This fraction is calculated from the amount

of hydrogen liberated above this temperature and is

not a uniquely determined quantity, for some hydrogen may be released from a small amount of organic matter. In our analysis the total water is 12.1

wt. %; 8.8% is H2O+ (105°C) (Table la) which is

in good agreement with the 8.95% reported by Jarosewich (1971) on a drier specimen of Murchison.

The matrix constitutes 77 vol. % of the meteorite

with the inclusion (mainly low iron olivine and

pyroxene) occupying the remaining 23 vol. %.

Assuming an average density of 3.3 for the inclusions, the density of the matrix is then 2.71 as

deduced from the measured density of 2.85 for the

TABLE la (wt. %) .—Comparison of chemical analyses of

Murchison meteorite

TABLE lb (atom %) .—Comparison of chemical analyses of

Murchison on a volatile (C, H, N, O, S) free basis

This Work

25.85

1.636

0.0713

31.99

0.146

2.822

0.374

0.218

33.12

2.20

1 .30

0.05]

0.21,

Calculated from the

Data of Jarosewich (1971)

26.46

1.564

0.0715

32.29

0.108

2.815

0.422

0.188

33.04

2.25

0.518

0.057

0.21,

meteorite as a whole. Thus the matrix comprises

73.4 wt. % of the meteorite and contains most of

the H2O + , which amounts to 12.0 wt. % (circumstantially almost equal to the total analyzed H2O).

TABLE 2a.—Electron microprobe analysis of Murchison

matrix

Fe

Cu

NiO

CoO

FeS

sio2

TiO2

Al,0 ,

2 3

Cr2°3

FeO

Fe2O3

MnO

MgO

CaO

Na2O

K20

P

2°5

2

H20(-)

SO,

3

S

S=

c

CO,

2

N

Total Fe

Total S

(1) See discussion in

(2) A calculated value

This Work

0.03

0.015

1.73

0.076

(1)

27.22

0.099

2.05

0.402

(1)

(1)

0.22

18.90

1.75

0.57

0.034

0.23

8.80

3.26

2.38

0.49

1.81(2)

1.91 (Total)

n.d.

0.096

(5)

20.44

3.24H

8

section - Wet Chemical Analysis .

. Total S -[S as SO, + elemental

(3) Sulfide sulfur included in FeS value.

(4) No elemental sulfu

(5) No summation since

(6) n.d. - Not determi

r detected.

values for FeS, FeO and Fe»Co are

I 3

ned.

Data of Jarosewich (1971)

0.13

n. d. (6)

1.75

0.08

7.24

29.07

0.13

2.15

0.48

22.39

n.d.

0.20

19.94

1.89

0.24

0.04

0.23

8.95

1.14

0.90

(4)

(3)

1.85

1.00

n.d.

99.80

22.13

3.00

S]

not assigned.

SiO,

C.

A 12°3

Cr203

Fe,0,

2 3

FeO

MgO

CaO

MnO

NiO

H,0

2

Sum

Si

Al

Cr

Fe

Fe+2

Mg

Ca

Mn

Ni

(OH)

1. Average values i

2. Oxides in no. 1

H20

+

 (see text)

3. 20% of Fe in no

1.

23.4

3.1

0.3

-

34.1

15.1

0.9

0.2

1.5

_

78.6

Number of

1.49>

1 0.23 1

> 1.73

0.01

JJ

1.81 •>

1.43

0.06 >I 3.39

0.01

0.08 J

4.54

For 40 spot analyses

recalculated to 88%

+3

. 1 assigned as Fe

4. No. 3 recalculated to 88%, H20 = 12

2.

26.2

3.5

0.3

_

38.2

16.9

1.0

0.2

1.7

12.0

100.0

ions*

by J . Nelen,

, H20 content

.0%.

3.

23.4

3.1

0.3

7.6

27.3

15.1

0.9

0.2

1.5

79.4

1.45 >

0.22

0.01

0.36-

1.42 ^

1.39

0.06

0.01

0.08 .

4.49

U.S.N.M., NiO

is calculated

4.

25.9

3.4

0.3

8.4

30.3

16.7

1.0

0.2

1.7

12.0

99.9

\

I) 2.04

[

)

1

I> 2.96

1

is our datum.

from bulk

Calculated to 9(0, OH).
NUMBER 10

The major element composition of the matrix was

obtained from electron microprobe analyses. The

average of three analyses kindly supplied by J.

Nelen of the National Museum of Natural History

are given in Table 2a. The low summation is due

to several factors: the major one is the water content; oxides present in amounts less than 0.3% were

omitted because of their extreme variability. Our

microprobe analyses contain amounts for C and S

of 1.7 and 3.3 wt. %, respectively, these elements

are probably not a part of the layer-lattice silicate;

additional factors involve the porosity of the specimen and the nonideality of the polished surfaces

of the fine-grained matrix. The averaged analysis

was recalculated to 88 wt. % to allow for the estimated water content of 12 wt. %.

The composition (Table 2a) is adjusted to assign

approximately 20% of the analyzed iron as ferric

so as to satisfy a tetrahedral to octahedral site ratio

of 2/3. The low silica content corresponds more

closely to that of a chlorite than to that of a serpentine. The estimated water content may be too

high since the calculated oxygen to OH ratio of

TABLE 2b.—Electron microprobe analyses of "spinach" phase,

Murchison meteorite

unity is less than the ideal ratio of 5 to 4. Based on

composition alone it does not appear to compare

favorably with any known layer-lattice silicate.

X-RAY EVIDENCE. — Approximately twelve X-ray

powder patterns (film) were taken of the black

matrix from several areas on different specimens of

the meteorite. Although sampling was done under

the binocular microscope so as to avoid visible

contamination, extra lines appeared on some patterns which were not common to others. All patterns, however, contain approximately nine lines in

common and these provided a starting point for

the identification (Table 3). In some cases the impurity lines could be assigned to either olivine or

calcite, but two prominent lines (intensity 3 to 5)

at 6.1 A and 5.4 A were not positively correlated

with each other. Since the 6.1 A line was generally

present on samples selected from unusually black

areas of the matrix, it was thought that this might

be due to an organic compound. Overnight treatment of these samples with various organic solvents

produced no effect on the patterns. But a five minute treatment with 2% nital eliminated the 6.1 A

line with no other effects to the overall pattern.

Except for the conclusion that the unknown phase

was acid soluble, no further attempt was made to

A 12°3

C r2°3

FeO

MgO

CaO

MnO

Sum

Si

Al

Cr

F e+ 3

(OH)

28.0

2.6

0.4

28.0

2.6

0.4

2.3

27.3

19.9

23.4

3.7

1. Associated with Fo 99 in chondrule, E. Olsen analyst.

2. Recalculated, assuming 7% Fe as Fe+ 3

3. Composition of associated olivine not determined. J. Nelen, analyst.

4. Recalculated, assuming 5% Fe as Fe

* (OH) set to 4.00, formula calculated on the basis of 7 oxygen equivalents.

TABLE 3.—X-ray powder patterns* of the matrix material

from the Murchison, Murray, and Mighei meteorites

Mur

d(A)

7.2

-

5.4

4

'

7 ?

4.3 j

3.9

3.62

3.58

-

-

-

-

2.70

-

2.53

2.43

2.30

2.16

2.03

1.79

-

1.57

1.54

1.49

1.44

chison

'I

10

-

1

Broad

Band

1

1

5

-

-

-

-

2

-

8

3

1

4

1

2

-

3

3

1

1

Murr

d(A)

7.1

6.0

5.4

4.7")

4.3 )

3.9

3.62

3.58

-

-

2.88

-

2.70

-

2.54

2.43

2.29

2.16

2.03

1.785

1.68

1 .575

1 .540

1.49

1 .44

ay

I

10

1

1

Broad

Band

1

1

8

-

-

1

-

3

-

6

4

1

3

1 +

2

2B

3

2+

1

1

Miqhei

d(A)

7.2

6.0

5.4

4.7

4.51

-

-

3.57

3.43

3.33

2.86

2.77

2.69

2.61

2.53

2.44

2.36

2.16

2.03

1.785

1.67

1.57

1.535

1.49

1.438

I

10

5

1

1

2

-

-

8

FT

FT

1

1

2-

1

10

1

1

6

1

4

IB

3

3

2

1

Assignments

C

A.S.

U

c

A.S.

C

?

c

?

?

?

A.S.

CM+CH

A.S .

CH

CM

C

CH

CM

CH

C

C

C

CH

C

*Fe radiation, Mn-filter, 114 mm Philips powder camera. Intensities are visual.

Abbreviations: B = broad; CM = monoclinic chamosite, CH = Hexagonal chamosite,

C = lines common to CH and CM; A.S. = acid soluble. U = unidentified fibrous phase.
6 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

identify it. Samples showing a 5.4 A spacing were

mounted and polished. These were found to contain several percent of two phases, which displayed

massive amorphous and fibrous textures, respectively. They are ubiquitous in all sections of Murchison studied (cf. "Poorly Characterized Phases").

The fibrous phase is characterized by a strong 5.4 A

reflection.

Based on the nine lines common to all patterns

of the matrix material certain similarities exist with

the septechlorite, chamosite, and the serpentine

(ferroantigorite).

Carroll (1970) noted that a trio of medium intensity X-ray peaks at 2.67, 2.40, and 2.15 A are

diagnostic for chamosites. Our matrix material patterns show this trio at 2.70, 2.44, and 2.16 (the small

shifts in d-spacings due to compositional differences). This, in itself, could be compelling evidence

to establish this material as chamosite. Our X-ray

pattern of ferroantigorite from O'Neil Mine,

Orange Co., New York (Field Museum sample

M3641), however, shows the same three lines present, 2.72, 2.43, 2.17 A. These, however, are not

uniformly of medium intensity, rather the 2.72

line is exceedingly weak. Because our 2.70 line is

stronger, and the trio approximates the intensity

pattern of chamosite, we regard a chamosite designation of the matrix material as a slightly better

possibility than ferroantigorite (or any other serpentine-group mineral). Bostrom and Fredriksson

(1966) have concluded that the matrix material in

the Cl meteorite, Orgueil, is a ferric chamosite

primarily on compositional grounds.

For comparative purposes X-ray powder patterns

were obtained on the matrix material of Murray

and Mighei, and these are presented in Table 3

together with that of Murchison.* Aside from a

few impurity lines the d-spacings of corresponding

lines on the three patterns are in agreement, but

significant differences exist in the relative intensities of some lines, especially those that correspond

to the prominent lines of either monoclinic or

hexagonal chamosite. The intensities of the line

at 2.43 A—monoclinic—vary inversely as those at

2.53 and 2.16—both hexagonal—(for a comparison

* Samples invariably contained impurities, as evidenced by

the spotty character of some lines; it was found that nonrotation of samples during exposure simplified the distinction between the fine-grained matrix and coarser grained

impurities.

of both forms of chamosite, see Brindley, 1951 or

ASTM card 7-315). It can be seen that the ratio of

hexagonal to monoclinic chamosite is greatest for

Mighei, intermediate for Murchison, and least for

Murray. Although this relationship may not be

representative of the matrix material in these three

meteorites, the fact that a mixing ratio exists for

the samples X-rayed supports the preference of

chamosite rather than a serpentine mineral as the

predominant mineral in the matrix material. When

present, the line at 6.1 A is removed from all samples when treated with 2% nital for five minutes,

in the case of Mighei, lines at 4.51, 2.77, and 2.61

are also eliminated by this treatment. It should be

noted that our pattern of Mighei shows a number

of differences when compared to the pattern published as "Murray F" by DuFresne and Anders

(1962) which they obtained from Mighei. Their

pattern contains 9 extra lines that can be assigned

to the strongest lines of olivine. Aside from the

olivine impurity, the remainder of the pattern is in

good agreement with ours.

As a further check on the properties of the matrix

material a series of heating experiments were undertaken. A sample of Murchison matrix was

TABLE 4.—X-ray powder patterns* of Murchison matrix material in an evacuated silica capillary following each stepwise

heating period.

Not

Heat

d(A)

7.2

5.4

3.58

2.70

2.54

2.44

2.17

2.12

1.79

1.57

1.54

ed

I

10

3

7

2

7

1

2

1

FT

3

2

3. 7 Days

245

d(A)

7.1

5.4

3.58

2.70

2

2

2

1

1

1

.54

44

.17

79

57

54

C

I

10

1

8

1

8

1

2

FT

3

2

7 7

?45

d(A)

7

3

3

3

1

9

58

33

2.97

2

2

2

85

70

54

2.44

2 16

2.04

1

1

1

1

Days

°C

I

10

1

7

FT

1

1

2

8

1

2

1

79 FT

57

54

48

2

1

1

1.7 Days

340

d(A)

7.1

3.58

2.97

2.70

2.54

2.44

2.16

2.05

1.79

1.72

1.61

1.57

1.54

1.48

C

I

10

7

2

1

8

2

2

2

1

1

FT

2

1

1

5.8 Days

340

d(A)

7.1

3.9

3.58

2.97

C

I

10

FT

7

3

2.70 FT

2.62

2.54

2.45

2.17

2.05

1.79

1.72

1.61

1 .57

1.54

1.48

1.31

FT

9

1

2

2

1

1

FT

2

1

FT

FT

24 Days

340

d(A)

7.1

3.58

2.97

2.70

2.64

2.54

2.44

2.16

2.05

1.79

1.72

1 .61

1.57

1.53

1.48

C

I

8

6

3

FT

1

8

1

2

3

1

2

1

2

1

1

1 .32 FT

12 Days

400°

d(A)

7.1

3.58

3.50

2.97

-

2.65

C

I

8

3

2

3

2

2.53 10

2.16

2.06

1.79

1.72

1.61

1.57

-

2

3

1

1

2

2

1.53 FT

1 .48

-

2

-

19 Days

450°

d(A)

7.4

I

2

3.60 FT

3.50

2.97

-

2.65

2.52

-

-

2.09

2.06

-

1.72

1.62

1.48

1.32

2

4

3

10

-

-

2

3

-

1

4

-

-

5

1

33 Da

450°C

d(A)

3.50

2.96

2.65

2.52

-

-

2.09

2.06

-

.72

.61

-

.48

.32

.092

.048

ys

I

-

FT

4

-

2

10

-

-

2

2

1

3

-

4

1

3

2

0.856 1

0.854 1

Phase

C

(1)

C

C

?

M

?

CM+CH

FeS

(2)

CM

CH

M

FeS

CH

M

M

c

c

M

FeS+M

M

M

Ma.

Ma2

*Cu radiation, Ni-filter , 114 mm Phil

Abbreviations: FT = fain t trace; CM

C = lines common to CM and CH; A.S. =

fibrous phase; (2) = line common to M

ps powder c Inte

:

 monoclinic chamosite; CH = hexagonal chamosite;

unidentified acid-soluble phase; (1) = unidentified

and CH; M = Magnetite.
NUMBER 10

sealed in vacuo in a silica capillary with a minimum of empty space and heated for various times

at increasing temperatures. After each heating

period the capillary was air quenched to room

temperature and X-rayed. The results are shown in

Table 4. The major effect is the decomposition of

the layer-lattice structure, which begins at 340°C

and is practically complete after the final heating

period at 450°C. Magnetite, not present in the unheated material, begins to form about 100°C lower

than the apparent decomposition temperature of

the silicate and becomes the major phase at 450°C.

A significant side effect involves the decomposition

of the unidentified fibrous phase (with the characteristic 5.4 A line) at 245°C to form a new phase,

Avhich is most probably troilite (lines at 2.65, 2.06,

and 1.32 A). Of minor importance is the occasional

appearance of weak lines as noted in the footnote to

Table 4. These may be due to local impurities

present along the length of the capillary.

A sample of ferroantigorite from the O'Neil

Mine, Orange County, New York, sealed in an evacuated silica capillary and heated at 450°C for 50

days showed that some alteration occurred to form

fayalite, but that ferroantigorite persisted as the

major phase. These differences observed for the

thermal stability of matrix Murchison material and

ferroantigorite support the X-ray results that they

are not identical. Unfortunately a clean specimen of

chamosite was not available on which to perform

similar experiments.

Aside from all of these considerations there are

problems attending the use of terrestrial minerals of

the septechlorite and serpentine groups as reference materials. Often many polymorphic forms exist

in a single terrestrial occurrence of a mineral that

may be characterized by one published powder

pattern. An example in point is the reported existence of eight polymorphs of cronstedite by Steadman and Nuttall (1963) for the type-locality in

Cornwall. A powder pattern for this mineral as

presented on ASTM card 17-470 could contain contributing reflections from several polymorphs. Since

these polymorphs were discovered on single crystal

photographs there is visually no assurance that each

has the same composition as the bulk material.

The relative amounts of these phases of uncertain

compositions may vary sufficiently in a meteoritic

environment to mask or obliterate a strict comparison with terrestrial counterparts.

Ultimately there may be little justification for

discussion of the nature of the matrix material for

carbonaceous chondrites; there may be several

minerals and/or coexisting polymorphs of several

minerals of various compositions. Kerridge (1969),

using selected area electron diffraction techniques,

has found a wide range of unit cell parameters for

meteoritic layer-lattice silicates, which suggested to

him corresponding variability in compositions.

A polished matrix specimen was treated with

warm concentrated phosphoric acid for 30 minutes.

A microscopic gridlike pattern of matrix material

was removed leaving "islands" of matrix standing

in relief. About half of the matrix was dissolved.

a

11

OJ mm

FIGURE 3.—a, Plate of olivine (Fo100), parallel to (100) , containing oriented glass stringers and blebs; b, plate of green

hydrated silicate called the "spinach phase" in text. Alternations of a and b impart a micaceous appearance to this type

of inclusion.
SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

This suggests that the matrix consists of at least two

phases.

OTHER LAYER-LATTICE SILICATE.—Outside of the

matrix, within some inclusions, we found a separate

and unique occurrence of a layer-lattice silicate.

This silicate may or may not be the same, mineralogically, as the matrix material, for its appearance

and mode of occurrence set it apart from the

matrix material; the two may not be related genetically. This silicate is characteristically a transparent spinach-green color and to distinguish it in our

discussion we will call it the "spinach" phase.

It is found in four distinctive settings: (1) interstitially between, and coating, forsterite (Fo 99)

grains; (2) as complete inclusions of "spinach"

within the black matrix; (3) interstitial to forsterite

(Fo 99) grains within some true chondrules (type

3 inclusions); and (4) as rhythmically spaced lamellae interleaved with olivine (Fo 99-50 plates)

(Figure 3).

The last type of setting with its distinctive platy

texture can almost be considered a separate type of

inclusion. Plates of unaltered olivine alternate with

isotropic or weakly anisotropic plates which vary in

color from light to dark green. The color is apparently related to the degree of development of the

spinach phase. The darker green platelets are very

fragile and give an X-ray powder pattern resembling (but not the same as) the patterns of the

matrix; whereas the lighter green plates give broad

lines of both a layer-lattice silicate and olivine. The

colorless olivine plates give good olivine patterns.

This material resembles that described by DuFresne

and Anders (1962) for Mighei and Murray: ". . .

olivine has been divided by the penetrating material into a series of thin parallel plates with rather

a micaeous appearance, although diffraction shows

nothing present but olivine and Murray F." The

authors consider Murray F to be an alteration product of olivine produced by the intervention of

liquid water, "the alteration having taken place in

the parent body." Our observations on these specific

occurrences in Murchison provide additional information but still leave some unanswered questions.

The texture of these "lit par lit" spinach-olivine

inclusions ends abruptly at the surrounding matrix.

In section there are no obvious adits leading to the

inclusion; additionally, nearby olivine crystals or

fragments within the matrix may be unaltered,

suggesting that the alteration is pre-Murchison in

origin.

The plates of olivine are always parallel to the

(100) plane, as evidenced by a centered acute bisectrix interference figure, and they contain numerous glassy inclusions of various shapes from

distorted spheres to elongated blebs or ribbons

(Figure 3). Glassy blebs within some of the plates

of olivine are oriented in directions parallel to or

45° to the extinction directions and thus occur

along crystallographic directions. We have not analyzed these glasses as most are only a few microns

wide in their shortest direction. Lacking compositions, we can say nothing about their origin or

why they are so numerous. Their abundance, however, suggests that they are somehow related to the

degree of olivine alteration. It is possible that the

spinach formed by the replacement of olivine plates

which were loaded with nonresistant glass. The

surviving unaltered olivine either contained discrete glass blebs protected by olivine, or perhaps

the unaltered glass was simply more resistant.

One clue that possibly illustrates the initial development of the spinach phase comes from a

chondrule in a thin section of Murray. Parallel

bands of olivine are interleaved with alternating

bands of light-green mottled isotropic glass. The

green is confined to the glass; bands of olivine are

unaltered.

The quality of the X-ray patterns for the matrix

material did not permit comparison of subtleties

that would allow more definitive interpretation.

Only 9 X-ray lines were obtainable in that case. On

the other hand, X-ray patterns of the green spinach

phase yield 14 relatively sharp lines that can be

assigned to a mixture of monoclinic and hexagonal

polymorphs of chamosite; a few weak unidentified

impurity lines are usually present.

In the case of the fourth setting, it was noted

that the plates of layer-lattice silicate visibly contained impurity phases. An X-ray pattern consisted

of 21 lines and was more difficult to interpret. It

appeared to consist of a mixture of chamosite,

serpentine, and other unidentified phases.

The composition of this spinach phase from a

true chondrule is presented in Table 2b, which

includes an analysis of the same phase obtained by

f. Nelen from an undetermined site in one Murchison section. It is apparent that this phase varies
NUMBER 10

in composition. Although sufficient data are lacking, this variation apparently has no relation to

the composition of the associated olivine; in our

occurrence (29.3 wt. % FeO) the associated olivine

is practically Fe-free. Both analyses can be calculated to 7 oxygen equivalents as no estimates of

H2O contents can be made. Compared with the

matrix material (Table 2a), smaller amounts of

Fe+3 are required to fill the tetrahedral sites, but

clearly there are too many octahedral ions in both

spinach analyses. This indicates that nonlayerlattice silicate impurities are present. They are

either amorphous or, if crystalline, are present at

levels not permitting X-ray identification. These

uncertainties nullify the possibility that the spinach phase is a simple in situ alteration product of

olivine.

OLIVINE

Olivine is the next most abundant phase, occurring in all four types of inclusions. It ranges in

composition—from grain to grain—from Fa 0 to

Fa 85, both as internally homogeneous crystals and

as strongly zoned crystals. Olivine will be discussed

in detail under "Textural Features" and "Mineralogical-Compositional Relationships."

CA-POOR PYROXENE

Both the orthorhombic and monoclinic forms of

the enstatite-bronzite series occur, compositions

ranging from Fs 1 to Fs 50. No zoning was observed.

Many of the orthorhombic crystals gave X-ray patterns of a disordered form (Pollack and Ruble,

1964) with considerable line broadening. Some,

however, showed normal ordered patterns. Pyroxene will be treated in more detail later.

C ALCIC-P YROXENE

Fragments of calcic-pyroxene occur within the

matrix, but are exceedingly rare. Partial analyses

performed on some grains gave Fe/ (Fe+Mg) ratios

of 0.06 to 0.09. Diopside has been found surrounding hibonite in minute white inclusions (cf.,

"Hibonite" and "Perovskite"). In one instance a

dark green augite grain was found.

FIGURE 4.—Polished section of an exceptionally metal-rich

area. Some troilite is present, but it is less than one percent.

METAL

Metal is not abundant. In the bulk analysis

(Table la) it amounts to only 0.03%. A few sections, however, contain abnormally high amounts

(Figure 4). It is found mainly within some olivine

grains, both in white inclusions and in true chondrules. Some rare isolated grains occur in the black

matrix or within Ca-poor pyroxene. Metal grains

range in size from submicron blebs up to 0.42 mm

in sections we studied. The very few large grains

were found isolated in the matrix and not in

olivine or pyroxene. The grains are smooth ovate

to spherical in shape, which is distinctly different

from the angular shapes commonly found in the

ordinary chondrites.

A group of metal analyses are given in Table 5.

These analyses are of metal grains within olivine

(both from white inclusions and true chondrules)

and isolated in the matrix. There are no systematic

chemical differences between the metals from these

three sites.

The outstanding features are the unusually high

Cr and P contents, from 0.20 to 0.96 wt. % and

0.28 to 0.37 wt. %, respectively. Metal from all

other classes of meteorites, where measurements

are available, carry only trace amounts of Cr (less

than 0.001%). Indeed, in most instances it is not

reported because it is presumably at low trace

levels only. Some of the metal in lunar lavas runs

up to 0.42% Cr (Taylor, Kullerud, and Bryan,
10

TABLK 5.—Electron microprobe analyses of metal grains in

Murchison

Location of grain

Four grains

within

single

chondrule

Two grains

within

single

chondrule

Six grains

in

black matrix

1

2

3

4

1

2

1

2

3

4

5

6

f Center

\Edge

f Edge

\ to

[Edge

Fe

93.8

94.6

94.0

93.7

90.8

92.2

92.1

93.5

94.0

93.6

93.7

93.1

92.0

Ni

5.6

4.3

4.0

4.9

7.4

5.6

5.5

5.0

4.8

4.8

4.8

6.3

7.0

Co

0.40

0.32

0.32

0.35

0.41

0.74

0.40

0.35

0.38

0.35

0.32

0.42

0.43

Cr

0.96

0.85

0.79

0.80

0.86

0.69

0.78

0.83

0.64

0.73

0.49

0.77

0.20

0.55

P

0.28

0.32

0.32

0.37

0.29

0.37

0.35

0.37

0.32

0.36

0.35

0.31

0.32

Sum

101.0

100.9

100.3

99.4

100.2

99.6

99.7

99.2

99.9

100.2

99.6

99.9

100.3

100.3

1971), which is still a factor of 1.7 less than the

average Murchison metal (0.7%). Only two grains

were large enough to test for Cr homogenity. Scanning across a large (0.42 mm) grain (isolated in

the matrix) showed a steady Cr profile of about

0.2% for about half the grain, then rising smoothly

to 0.55% at the opposite edge. In the other case, a

grain of metal within forsterite in a true chondrule showed a central core of 0.96% Cr falling to

0.85% at the edges.

The average P content of these metal grains is

0.33%. The large 0.42 mm matrix grain was

scanned for phosphorus homogeneity. The grain

ran generally around 0.32% with a few spots showing up to 0.60%. These spots may be due to small

specks of phosphide, although none were visible.

No such spot was wide enough for microprobe

analysis.

Because of the unusual chemistry of the Murchison metal careful wavelength scans were performed,

especially for Si, Ti, V, Mn, Cu, Mo, W, and Pt.

None of these was present above detection limits

(about 0.05%) although one grain showed a possible Pt content of about 0.07%.

We assume the metal is kamacite; however, we

do not have any data that totally rule out other

structural states. The grains analyzed were generally

too small to scan for homogeneity. The one large

(0.42 mm) grain was relatively homogeneous in Ni

SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

content, showing a slight rise from 6.3% to 7.0%

going across the grain; however, a few isolated

spots within it showed lows of 4.7%. Etching of

larger grains revealed no observable structural features, plessite areas, Neumann bands, etc.

The recent study of the Fe-Ni-P system by Goldstein and Doan (1972) shows that kamacite with up

to 0.4% P and up to 7% Ni can exist without

schreibersite being formed down to a temperature

of 550°C. These are the upper limits of P and Ni

values in the Murchison metal. Grains of kamacite

with as little as 0.3% P and 4% Ni could represent even lower temperatures (450-500°) without

the formation of schreibersite. The effect of up

to 0.9% Cr on this is unknown.

The unusual content of Cr in the Murchison

metal will be discussed under "Chromium and Phosphorus in Metal." We also note that a complete

chondrule made of metal, with some schreibersite,

was found in one single instance. It is described

under "Phosphorus Minerals."

SULFIDES

Both troilite and pentlandite were found, the

former several times more abundant than the latter. The predominance of troilite over pentlandite

in the case of Murchison disagrees with the reverse

relation in other C2s (Ramdohr in Mason, 1962-

63). The troilite commonly shows a mottled appearance due to finely disseminated pentlandite

(Figure 5). The mottling ranges from submicron

FIGURE 5 -Pentlandite (light) within troilite matrix,

immersion, scale bar is 10 microns.
NUMBER 10 11

size up to 5-micron patches of pentlandite. The

nickel content of the troilite ran as low as 0.2 wt. %

where the mottling was absent entirely, up to

1.7% where the mottling was very apparent. It

would appear that the nickel content of the troilite

is quite low, comparable to values in other common meteorite types, and that values above 0.2%

are due to the minute admixture of pentlandite.

Separate analyses of the larger pentlandite grains

give Ni=24.4%.

Texturally most of the troilite occurs as angular

grains in the matrix; it has a distinct fragmental

appearance and is not associated with metal grains.

This is in marked contrast to some C3 chondrites,

where troilite commonly rims metal grains. Point

counting of troilite and pentlandite grains gives

an abundance of 0.13 wt. % which is considerably

less than the amount that is computed from the

bulk chemical analysis, 7.24 wt. % (Jarosewich,

1971). This disparity is because the bulk of the

sulfur is not present as troilite but must be finely

divided and dispersed in the black matrix. As such

it is not visible in an interior section, but its presence is revealed within a band 0.3-0.6 mm wide

adjacent to the fusion crust. Atmospheric heating

has formed profuse amounts of a light-yellow phase,

softer and less reflecting than troilite, which resulted from a reaction between matrix sulfur and

iron in unknown states. This soft-yellow phase may

be related in composition to the poorly characterized sulfur-bearing phase (see "Poorly Characterized Phases) where it is not associated with the

fusion crust, but the two phases differ markedly in

mode of origin.

PHOSPHORUS MINERALS

No phosphates were seen; however, the phosphide schreibersite occurs as blebs in the chondrule of metal noted earlier, and as rare specks

within metal grains in the black matrix. It was

never observed in metal grains contained within

olivine crystals or contained in true chondrules.

This is the first time schreibersite has been reported

from any carbonaceous meterorite.

CALCITE

Calcite grains were ubiquitous in all sections

studied. It occurs principally in the black matrix;

however, X-ray patterns of some white inclusions

showed it to be present there in small amounts.

Grains range from a few microns up to 80 microns.

X-ray, optical, and microprobe work show it to be

free of any cations other than calcium. The grains

are frequently polysynthetically twinned.

WHEWELLITE

Whewellite, the calcium oxalate monohydrate,

Ca (C2O4).H2O, was found in one white inclusion

between olivine grains. The X-ray pattern matches

the ASTM reference pattern perfectly with no

extraneous lines present. Over ten lines were observed. The occurrence in Murchison is logical

considering the relatively high organic and calcite

content of the meteorite. Terrestrially whewellite

is found in organic-rich sediments, plant cells, some

kidney stones, and occasionally in hydrothermal

deposits.

At 230°C whewellite decomposes to the anhydrous salt (Freeman and Carroll, 1958). This temperature, however, cannot be used as a maximum

temperature indicator here because the anhydrous

salt is hygroscopic (Miller, 1953). At lower temperatures it would revert to the monohydrate in the

water-rich environment within the meteorite. At

best a maximum of 480°C may be indicated where

the anhydrous salt decomposes to form CaCO3+CO

(Freeman and Carroll, 1958).

SPINEL GROUP MINERALS

Three minerals of this group are found in

Murchison: spinel proper is found as inclusions

within olivine and in white inclusions; chromite

is found in white inclusions and as fragments in the

black matrix; spherules of magnetite are found in

the matrix and occasionally within troilite. The

NiO content of the magnetite within the troilite

is 0.8%, whereas no nickel is found in the matrix

magnetite spherules.

Spinel proper varies considerably in composition,

color, and cell size from grain to grain, from pure

MgAl2O4 to compositions with considerable Fe

and Cr (Table 6).

All these members of the spinel group occur in

trace amounts only. Chromite is somewhat more

abundant than the others. Magnetite is quite

variable in quantity from section to section, al-
12 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

TABLE 6.—Electron microprobe analyses of spinels

A12O3

Cr2°3

Tl0 2

FeO

MgO

CaO

Sum

n

a(A)

Al

Cr

Ti

Fe+2

Mg

Ca

R

+ V

R

+2

Notes

Nos. 1

Compos

Nos. 4

Compos

No. 6

n.d. =

Mn, Zr

1

71.1

0.7

0.3

0.1

28.8

n.d.

101.0

1.722

8.091

Numbe

15.78

0.10

0.05

0.01

8.08

-

4

 15.93

8.09

to Table 6.

, 2 , and 3 are 50-120 urn

itions of associated ol

and 5 are 6 ym grains '

2

46.5

25.4

0.3

10.9

18.3

n.d.

101.4

1.855

8.182

rs of ions

11.75

4.30

0.05

1.96

5.85

-

16.10

7.81

grains fror

ivines are:

3

59.9

12.8

0.3

2.5

25.7

n.d.

101.2

1.780

8.135

on the basis i

13.95

1.99

0.05

0.42

7.57

_^_

15.99

7.99

n 3 different

FaQ(No. 1),

inside of glass inclusior

ition of host olivine is Fan , .

0.6

is a 12 urn inclusion in

not determined

Fa0.3-

, K, Na are below background.

4

67.4

2.6

0.2

0.6

27.5

1 .6

99.9

n.d.

n.d.

Df 32(0)

15.34

0.39

0.03

0.09

7.91

0.34

15.76

8.34

olivine-spinel

Fa1Q (No. 2),

I la and lb res

5

67.3

2.1

0.2

0.6

28.1

0.1

98.4

n.d.

n.d.

15.46

0.33

0.04

0.09

8.16

0.02

15.83

8.27

white ir

F a 2 - 7 (*

p. Table

6

69.6

0.7

0.2

0.5

28.3

0.0

99.3

n.d.

n.d.

15.73

0.12

0.03

0.08

8.09

0.0

15.88

8.17

iclusions.

j . 3) .

8.

though generally lower than chromite. The general

low abundance of magnetite runs counter to many

statements in the literature that it is a significant

phase in all carbonaceous chondrites. Small chips

of Murchison are noticeably magnetic. The magnetism, however, may be due to a relatively abundant

phase which we have been able only to poorly

characterize as a possible Fe-S-O phase (see "Poorly

Characterized Phases").

The chromite varies moderately in composition

from grain to grain (Table 7). The compositions

are notably different from chromites in all other

meterorite types (Bunch, Keil, and Snetsinger,

1967; Snetsinger, Keil, and Bunch, 1967; Bunch,

Keil, and Olsen, 1970; Bunch and Keil, 1971). The

analyses reported in Table 7 are for individual

angular fragments dispersed within the matrix in

one probe section. These chromites are generally

characterized by their A12O3 contents (av. = 14.8

wt. %) and in this respect they are markedly different from those in the ordinary chondrites (av.

about 6%), and resemble those from terrestrial

igneous rocks (av. about 16%). Of all the meteoritic

chromites analyzed in the four references cited,

exclusive of those in the brecciated mesosiderites,

only a few have A12O3 contents approaching those

in Murchison, and they occur in a few members

from highly fractionated classes such as the hypersthene achondrites and some irons. If the C2s

contain primitive matter, it is surprising that the

compositions of the Murchison chromites are so

different from those in the abundant chondrites.

It is difficult to imagine some process whereby

these compositions might be brought to the compositions of ordinary chondritic chromites, especially at temperatures around 800°C where most chondrites are thought to have equilibrated. Only small

differences in the compositions of chromites exist

between the various metamorphic grades of chondrites, hence metamorphism has only a minor effect

in altering chromite compositions. The compositional differences between Murchison and ordinary

chondritic chromites were consequently established

in some primary process. We can only speculate

that the temperatures involved were rather high

and close to those in the magmatic range that

effected the fractionation of some meteorites with

TABLE 7.—Electron microprobe analyses of chromites

C r2°3

A l 2 0 3

V

2°3

Ti0 2

FeO

MgO

MnO

Cr

Al

V

Ti

F e + 2

Mg

Mn

47.4

17.3

0.6

0.9

26.7

6.2

0.3

99.4

9.93

5. 40

0. 13

0. 18

5.92

2.45

0.06

46.8

17.7

0.5

0.7

28.4

5. 7

0.2

100.0

Nun

9.80

5.52

0.11

0.14

6.28

2.24

0.05

47.1

18.5

0.4

0.6

25.4

8.1

JLJL

100.3

nbers of

9.65

5.65

0. 08

0.12

5.51

3.13

0. 05

60.2

3.2

0.6

0.5

32.9

1 .3

0.3

99.0

ions or

14.07

1.12

0.14

0.11

8.14

0.57

0.07

48.9

15.7

0.8

1 .6

27.4

5.7

0.3

99.4

l the

10.25

4.90

0. 18

0. 32

6.07

2.24

0.06

51 .4

10. 7

0.7

1 .7

29.3

4.5

0. 3

98.6

basis of

11 .33

3.52

0.15

0.35

6.84

1 .89

0.07

41 .9

22.3

0.6

0.9

27.7

6.9

0.2

100.5

"32(0)

8.49

6.73

0.12

0.17

5.95

2.63

0.05

50.3

14.0

0.7

1 .2

27.2

6.7

0.3

100.4

10.60

4.40

0.14

0.24

6.07

2.66

0.06

49.2

14.2

0. 7

1 .4

28.2

5.8

0. 3

99.8

10.47

4.51

0.15

0.29

6.34

2.33

0.06

15.

8.

64

43

15.

8.

57

57

15.

8.

50

69

15.

8.

44

78

15.

8.

65

37

15

8

.35

.80

15

8

.51

.63

15.

8.

38

79

15

8

.42

.73

24.0 7 24.1 4 24.1 9 24.2 2 24.0 2 24.1 5 24.1 4 24.1 7 24.1 5

Redistrib u

Fe as Fe

;Fe + + + 8

!

+ 3

+ R

+ 4

 15

!

+ 2

 7

,um 23

tio n

+

.0

.99

.89

.88

of

8.

15.

8.

23.

lor

0

95

01

96

is to

11 .

15.

8.

23.

al 1

0

96

01

97

ow

9

1 5

7

23

t o r

. 0

.98

.95

.93

a n

8

16

7

23

ass

.0

.01

.83

.84

1 gn

10

15

8

23

ed

.0

.87

.02

.89

perc

1 0

1 5

7

23

enta

.0

.97

.93

.90

ge o

1 1 .

15.

8.

23.

f total

0

91

03

94

11 .

15.

7.

23.

0

93

94

87

Note to Table : The numbe r of divalen t ions exceed s the ideal numbe r of

8 and the sum of the quadrivalen t and trivalen t ions is less than the

ideal numbe r of 16 . This indicate s tha t eithe r ferrou s o r ferri c ions

a re in 6-fold coordination . For illustrativ e purposes , we have recalcu -

lated each analysi s assumin g that from 8 to 11 wt . % of the total Fe may

be presen t as Fe but no case is mad e for its presence . The departur e

in the total numbe r of cation s from 24 may be the resul t of analytica l

error .
NUMBER 10 13

distinctive compositions such as the irons and

hypersthene achondrites. These observations clearly

argue against the derivation of ordinary chondrites

from C2 chondrites by any process short of melting.

LAWRENCITE (?)

On many (not all) freshly broken and fusioncrust-covered surfaces we observe scattered, spotty

"bleeding" taking place slowly. The bleeding

consists of patches, up to several millimeters, of

hydrated red iron oxide. In the past such bleeding,

especially in irons, has been attributed to the presence of unstable lawrencite. Our attempts failed

to definitely identify lawrencite. Whatever unstable

phase is causing this, its distribution is not uniform.

Individual specimens vary from no spots, to a few

scattered spots, to numerous ones. In general, the

spots tend to cluster into areas up to a centimeter

across.

sion had higher indices of 1.80 and 1.77. Hibonite

in Murchison marks the first occurrence of this

mineral in a C2 meteorite. The blue color and

absence of associated gehlenite serves to distinguish

this occurrence from those reported in the C3s.

PEROVSRITE

Scattered euhedral crystals of perovskite, CaTiO3

(2 to 4 microns), occur with diopside and spinel

which surround patches of hibonite. This is similar

to the occurrences in Allende and Leoville in which

hibonite is rimmed by perovskite. In those C3

chondrites, however, gehlenite is an accessory mineral. No gehlenite was found in Murchison. Perovskite was identified by its characteristic X-ray

powder pattern. A partial probe analysis (uncorrected amounts vs. rutile and grossular standards)

gave, in wt. %, 55 TiO2 and 43 CaO as compared

to an ideal composition of 59 TiO2 and 41 CaO.

HIBONITE (CaAl12O19)

Some very rare white inclusions, 100-150 microns

in diameter, have intensely colored blue centers of

microcrystalline hibonite needles, the largest 3 x 10

microns. X-ray powder patterns of the blue concentrates were predominantly those of hibonite

with minor perovskite. Line spacings and relative

intensities of the hibonite pattern were identical

to those reported for hibonite from the Leoville

meteorite (Keil-and Fuchs, 1971). The surrounding

white material is spinel and perovskite which may

be associated with diopside. One diopside-bearing

inclusion was mounted and probed. Diopside forms

the outer surface with an intergrowth of diopside,

spinel, and perovskite making up the mantle which

encloses in turn a core of hibonite. Because of the

small width of the hibonite needles, only a partial

analysis could be obtained: in wt. %, A12O3 74.5,

CaO 8.2, MgO 2.9. It is suspected that several percent of titania may be present analogous to one of

the hibonite compositions found in both Leoville

and Allende; however, during the course of the

analysis epoxy-bubbling obscured the surfaces and

forced us to terminate the analysis.

Optically, the needles are strongly pleochroic: e

= colorless, to — intense blue; refractive indices

are 1.78 (e) and 1.75 (co); grains from one incluSULFATES

Glistening plates (up to 40 microns) of gypsum

were found in localized areas on the surfaces of

some hand specimens (Figure 6). X-ray patterns

were of excellent quality and contained no extra

lines. Qualitative microprobe scanning showed no

cations other than calcium present above the 2%

level. By a series of observations on fresh surfaces

FIGURE 6 Scanning electron microscope photograph of gypsum crystals that occur in localized areas on some freshly

broken fragments. Scale bar is 20 microns.
14 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

it appears that gypsum does occur in Murchison as

a pieterrestrial phase filling localized short, discontinuous, thin veins. Evaporation on surfaces

apparently causes redeposition of intergranular

gypsum as large plates. We examined specimens of

the C2, Cold Bokkeveld, which have fracture surfaces created by sampling breakage in museum

collections over many years. All of these postterrestrially made surfaces are covered by numerous,

outward-projecting plates of gypsum.

No other sulfate phases were found; however, it

is possible others may be present. This is inferred

from the appreciable amounts of Na and Mg in

the water-soluble fraction determined in the bulk

chemical analytical results (see "Chemical Analysis

Discussion and Comparison").

FIGURE 7.—Assorted calcium aluminum silicate glass inclusions within olivine: a, largest inclusion found is 36 microns in diameter and contains a void bubble. Smaller inclusions are

present but are not in focus; b, 18-micron inclusion with void bubble and spinel crystal attached to outside surface of inclusion. Smaller inclusions (not in sharp focus) do not have

spinel crystals; c, elongated inclusion (11 by 29 microns) containing void bubble and euhedral

spinel crystal, d, olivine fragment (220 microns in diameter) containing numerous inclusions

elongated parallel to extinction directions.
NUMBER 10 15

GLASSES

Rare shards of glass that yielded no X-ray pattern

were observed in some polished sections. In addition, most true chondrules (type 3 inclusions)

contain small amounts of glass. The compositions

vary moderately and average around 77% SiO2,

14% AlaO3, 9% CaO, and less than 1% of Na2O

+ K2O. Of special interest is the occurrence of

ovate glass inclusions (up to 36 microns in diameter)

within single olivine crystals that are isolated in the

matrix (type 1 inclusions, Figure 7). Olivine grains

within the loosely consolidated multigrained aggregates (type 2 inclusions) also contain these inclusions. The latter occurrence has not been studied in

detail, so our description and discussion of the

inclusions apply only to those within the isolated

subhedral to euhedral olivines.

These inclusions are similar in appearance to

those noted in the Chainpur chondrite by Dodd

(1969) and to the melt inclusions in lunar and

terrestrial olivines described by Roedder and Weiblen (1971). An inclusion may or may not contain

void bubbles, spherules of metal, an iron sulfide, or

euhedral spinel crystals. Interior walls of some void

bubbles are lined with an iron sulfide (presumably

troilite), suggesting that a sulfur-containing vapor

occupied the bubble volume at elevated temperatures. The size of the bubbles varies considerably,

and there appears to be no correlation with the size

of the inclusion. For twelve inclusions measured, the

volume percentage of bubble to inclusion varies

from 1 to 14; some inclusions have no bubble. This

variation in bubble size cannot easily be accounted

for by a simple differential contraction mechanism

between inclusion and host during cooling. Alternatively, bubble occupancy by vapors under varying pressures may account for the observed variation. The smooth ovate shapes of the glass inclusions (most are spherical but some are elongated)

indicate that they formed from a liquid phase.

Aside from the occasional presence of spinel (Table

6), inclusions contain no other nonopaque crystalline phases; the glasses have not devitrified. The

persistence of a glass during cooling is in agreement

with the observations by Roedder and Weiblen on

lunar olivines where, with one exception, inclusions

less than 22 microns remained all glass. Our largest

glass inclusion is somewhat larger, 36 microns.

Microprobe analyses of these glasses (Table 8)

TABLE 8.—Electron microprobe analyses of glass inclusions

in olivine

Incl. No.

la

lb

2

3

4a

4b

4c

5

6

7

8

9

10

11

Av.

SiO,

48.2

48.1

45.4

63.1

45.4

43.6

54.7

44.9

53.1

49.4

74.2

57.3

47.7

53.7

52.1

CaO

17.0

21.3

21.6

10.7

22.9

23.8

17.3

20.4

17.4

21.1

9.0

17.4

20.9

12.8

18.1

A12O3

27.4

21.6

25.7

12.9

25.2

21.0

25.0

28.0

23.7

24.1

8.7

17.3

24.6

16.5

21.6

FeO

0.2

0.3

0.2

7.1

0.1

0.2

0.1

0.2

0.2

0.1

2.0

0.1

0.2

6.8

1.3

MgO

6.7

3.6

4.6

2.6

3.3

9.4

1.6

3.8

4.0

3.7

2.2

7.5

3.7

1 .7

4.2

MnO

0

0

0

0.1

0

0.03

0

0

0

0

0.1

0.03

0.03

0.1

0.03

K20

0

0

0

0

0

0

0

0

0

0

0.2

0.1

0

0.4

0.05

Na2O

0.01

0.01

0.01

0.3

0

0

0.2

0

0

0.03

1.4

0.5

0.03

1.8

0.3

TiO2

0.9

1.1

0.9

0.6

1.0

2.1

0.3

0.9

0.6

0.6

0.4

0.5

0.8

0.8

0.8

Cr2O3

0.2

0.1

0.2

0.2

0.2

0.1

0

0.2

0.3

0.1

0.2

0.3

0.3

0.03

0.2

Sura

100.6

96.1

98.6

97.6

98.1

100.2

99.2

98.4

99.3

99.1

98.4

101.0

98.3

94.6

98.7

Notes: (1) la and lb are 2 separated inclusions in one olivine grain; 4a is

a homogeneous inclusion which is isolated from the intergrowths

of 4b and 4c in the same olivine grain; remainder are single inclusions

in different olivine grains.

(2) The fayalite content (in mol. I) of host olivines is 0-1 except for

the following: No. 3 (25-45), No. 8 (3-8), No. 11 (23-35).

show wide variability in composition, though individually they are of uniform composition. One

bleb, however, contained two glass phases exhibiting distinctive reflectivites in the section. Their

compositions are given as 4b and 4c in Table 8.

Both phases are intergrown. Compositional features

common to most of the individual analyses are the

high Ca and Al and low alkali contents and thus

are very different from the alkali-rich glasses observed in unequilibrated ordinary chondrites

(Kurat, 1967; Fuchs, 1968; van Schmus, 1967). Ca

and Al rich inclusions are found in C3 chondrites,

but consist of several crystalline phases. The enrichment of Ca and Al within small areas in both

C2 and C3 meteorites suggests a common source

for this material in both types of meteorites, but

not necessarily a genetic relation between them.

Since the melt inclusions in Murchison olivines

differ in composition, it might appear that they did

not originate from a common source; this conclusion, however, may not be valid. The average

weight ratio of Ca/Al of all glasses is 1.13, which
16 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

is not too different from that of 1.09 for all chondrites and basaltic achondrites (Ahrens, 1970).

Thus these glasses may be primordial condensates

from a gas cloud that supplied all Ca and Al to

meteoritic matter. Further implications will be

discussed later under "Summary and Discussion of

Observations."

It should be pointed out, incidentally, that there

is a relationship between the FeO content of a

given glass bleb and its host olivine. Glasses containing less than 0.3 wt. % FeO occur in unzoned,

iron-poor olivines. The three relatively FeO-rich

glasses occur in zoned olivines, the average FeO

content of which increases with that in the glass.

This correlation probably reflects the FeO environment of the source material and does not result

from an in situ diffusion of iron between inclusion

and host. Microprobe traverses (1 micron beam

diameter) show that no compositional gradients

exist between host and inclusion. Abrupt changes

in composition are confined to bands 2 microns

wide. Zoning in host olivines is not influenced by

the presence of inclusions.

Melt inclusions in minerals from igneous rocks

may be formed by trapping fluid during fractional

crystallization, the composition of a melt inclusion

is then in equilibrium with its host at the temperature of the liquidus. Moreover, all inclusions within

a single host should have the same composition.

With regard to the latter condition, we have data

for two such olivines, both of which contain glasses

that differ in composition (glasses 1 and 4, Table

8). While it is possible that an olivine crystal growing in a magma could trap melt inclusions of

different compositions, we can find no other evidence

for a magmatic origin for these olivines.

A few preliminary heating experiments on

olivines with unanalyzed inclusions were performed

at 100°C intervals from 1200 to 1400°C for periods

of several hours followed by air-quenching to room

temperature. About six inclusions within each of

two crystals were observed microscopically and

photographed before and after each heating period.

In a few cases, crystals of unknown compositions

appeared in glass (which initially was all glass)

and then disappeared after heating to higher temperatures. Either solution of some olivine had

occurred to change the composition of the inclusion

(some inclusions did become larger), or some annealing occurred and was erased at the higher temperature. The lowest liquidus observed was between 1200 and 1300°C as indicated by a shift in

bubble position, but bubbles in other glasses in

the same olivine did not move even after 1400°C.

These observations support the compositional evidence above that different inclusions within an

olivine crystal have different compositions. Furthermore, their compositions in some cases would have

been altered if they coexisted with their host under

these heating conditions.

Phase diagrams can be examined to test for inclusion—host equilibria. The normative composition (wt. %) for the average for all glasses in

Table 8 is 60% anorthite, 27% diopside, and 13%

silica. But because the compositional range is

appreciable, each can be treated separately. For

simplicity FeO is added to MgO. The major component oxides then lie within the quaternary

system CaO-Al2O3-MgO-SiO2. The diagrams at one

atmosphere of Prince (1954) and Morey (1964)

are applicable for a few compositions, but for most

compositions the diagrams of Osborn et al. (1954)

are more appropriate as they present planes in the

tetrahedron for constant alumina contents in increments of 5% in the range from 5 to 35%. The

major conclusion deduced from these glass compositions is that they are not in equilibrium with

olivine at liquidus temperatures and therefore cannot represent compositions of melts from which

olivine crystallized. There is no olivine primary

phase field in planes with constant alumina equal

to or greater than 25%. Eight of the glasses lie

close to or within these planes. Three glasses (lb,

4b, 9) lie within the anorthite field; cristobalite or

tridymite are primary crystallates for glasses 3 and

8, and number 11 has too low a summation for

consideration.

Two melt inclusions (la and lb) contain euhedral spinel crystals. The question arises whether

spinel crystallized in situ from a melt higher in

MgO and A12O3 than the present melt compositions. If this be true, then the initial composition

of la (for example), adjusted to include the

amount of observed spinel (33 wt. percent), becomes in wt. percent: SiO2 32.1, CaO 11.8, A12O3

40.7, FeO 0.4, MgO 13.7, TiO2 0.7, and Cr2O3 1.1.

This composition has not been observed for any

spinel-free inclusion. Furthermore, euhedral spinels

(Fe- and Cr-free) are found within olivine not associated with a melt inclusion. This suggests that
NUMBER 10 17

euhedral spinel predated formation of melt inclusions and olivine. Early-formed spinel could have

nucleated later condensates.

As was mentioned earlier, in appearance these

glassy inclusions resemble the melt inclusions

found in olivines that crystallized from magmas.

Roedder (personal communication) in a preliminary review of our observations believes that both

host and inclusions can be explained as being derived from a magma. We suggest an alternate

hypothesis—that the glassy inclusions were frozen

liquid droplets incorporated into olivine, which itself did not crystallize from a magma. Following

are several reasons for this suggestion:

1. Single and relatively large olivine crystals in the

matrix are not associated with any other adhering

crystalline material. A meteorite type consisting of

only olivines (most of which are practically Fefree) and contain melt inclusions is unknown.

2. Aggregates of olivine grains that may contain

glassy inclusions are loosely consolidated. This state

of aggregation appears contrary to a magmatic

origin.

3. We have noted olivines with inclusions within

1-2 mm chondrules in the Allende C3 meteorite.

The inclusions are similar in appearance to those

in olivines from both igneous rocks and to those

in Murchison. Similarity in appearance, however,

does not necessarily signify a common mode of

origin. Clearly, chondrules solidified as discrete

systems of millimeter dimensions and did not

crystallize in a magma chamber.

4. The C2s, next to the Cls, contain elemental

abundances that approximate solar abundances.

Most, if not all, of the components of C2s must

have condensed from primordial matter. Thus,

their silicates and metal must have been closely

associated with a condensation process and not

with a fractionating magma. Further implications

of this condensation process will be discussed later

in the summary.

POORLY CHARACTERIZED PHASES

Two ubiquitous minor phases are present in all

polished sections studied. Both are soft and exhibit a dull beige color in reflected light, but they

differ considerably in form and mode of occurrence.

The first of these is massive in appearance, mottling is usually present, masses are optically isotropic though sometimes showing faint undulatory

extinction. Characteristic shapes observed vary:

(1) regular spheres resembling chondrules, (2)

angular to irregular pieces with serrated edges (Figure 8a), and (3) irregular rounded blebs (Figure

8b). The first two are most often found within

the matrix, while the blebs occur within or between

olivine grains in white inclusions. Based on shape

alone, the blebs might have replaced preexisting

metal where it was exposed to attack along fractures or grain boundaries. It is typical that metal

securely protected within olivine shows no alteration. On the other hand, isolated blebs of this

FIGURE 8.—Various shapes of massive Fe-S-O phase: a, irregular form (0.3 mm long) in Murchison matrix. Note the

variegated texture and what appear to be drying cracks; b,

oblate and oval forms in granular olivine inclusion. Smaller

bright spots are metal. Width of field is 0.5 mm.
18 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

massive phase show no channel fillings leading to

them. If metal within these inclusions were the

precursor, then the replacement must have occurred

prior to incorporation of the inclusions in Murchison, since unaltered metal coexists within the

matrix. As can be seen from the photographs, what

appear to be drying cracks are usually present.

Blebs of this phase can sometimes be removed easily

from white inclusions; they are highly magnetic

and give no X-ray powder pattern. The overall

weak magnetism of the matrix material of Murchison may be due to inclusions of this phase.

In occurrences (1) and (2) above, the edges of

these masses are slightly corroded and embayed.

This could represent either of two things: direct

reaction with the matrix material or reaction with

some liquid or gaseous phase that, at some time in

the preterrestrial history of the meteorite, passed

through the permeable, fine-grained matrix and

attacked this phase or some preexisting phase. Most

of the masses show diffuse edges which may represent more advanced stages of reaction. This massive

phase occasionally contains minute blebs of metal

or troilite and pentlandite.

In a few instances patches of a highly anisotropic

phase consisting of a criss-cross matting of fibers or

plates (5 to 10 microns long) are contained within

an isotropic groundmass resembling the massive

phase. This fibrous or sometimes platy phase is

the second poorly characterized phase seen in

Murchison. Some typical occurrences are shown in

Figure 9.

The anisotropy and reflectivity of these fibers in

polished sections approaches that of graphite and

may easily be mistaken for it. X-ray patterns show

one sharp line at 5.4 A and a weaker line at 2.72

A. The pattern could not be identified.

It is not clear if these two phases are related. It

is possible the massive material represents an alteration of the fibrous material, or the converse, that

the fibers represent a crystallization from the amorphous phase. On the other hand a cluster of fibers

do occur alone within the matrix in one instance,

and in several other instances clusters of fibers were

found rimming and projecting into large calcite

crystals (Figure 9c). The fibers are clearly much

lower in abundance than the massive, amorphous

phase.

Many of the properties we have noted for these

poorly characterized phases resemble those detv.

FIGURE 9.—Photographs of unidentified highly anisotropic

fibrous and platy phase. Oil immersion, reflected light: a,

fibers and plates embedded in matrix. Scale bar is 20 microns; b, interlocking plates within matrix. Scale bar is 20

microns; c, fibers within and bordering polysynthetically

twinned calcite crystal.
NUMBER 10 19

scribed for several types of an unknown phase (or

phases?) noted by Prof. Ramdohr (1963) in the

Mighei C2 meteorite. He suggested that it might

be a new Fe-C-S mineral with low Ni content and

that its low hardness indicated a layered structure.

Our X-ray results for the fibrous or platy phase

would appear to confirm a layered structure, but

we have not attempted to gather any compositional

data because of the narrow width (1-2/*) of the

fibers and platelets. Our probe results for the

massive phase indicates a more complicated composition.

Averaged microprobe results for the massive

phase are, in weight percent (with ranges, where

available, in parentheses): S 17.6 (16-19), Fe 42.0

(37-45), Ni 6.1 (5.9-8.2), Cr 1.6 (1.4-2.5), C 0.2,

P. 0.3, O 31.0, sum = 99.7. Approximately fifteen

areas of this phase on two separate probe sections

were analyzed. Wavelength scanning showed no

other elements present in detectable amounts (specifically no Cl, F, or Mg and only a faint trace of

Si). The fact that the sum is close to 100% is

fortuitous, as our accuracy for oxygen was low. The

result for oxygen may at best be semiquantitative,

but even this is significant. The stoichiometry does

not fit that of any known oxysalts of sulfur: the

atomic Fe+Ni + Cr to sulfur ratio is 1.6, whereas

most known compounds are unity or less. Some

hydrated oxysulfates exist with similar stoichiometries but none close enough to draw any conclusions. This massive phase was determined to be

water insoluble, hence it does not contribute to

the soluble sulfate content of the bulk chemical

analysis of Murchison.

Regardless of what kind of compound this represents, the association of Fe with both Ni and Cr

make it impossible to postulate a simple alteration of troilite or pentlandite.

In the heating experiments on the matrix material described earlier ("X-ray Evidence" and Table 4), we note that this fibrous phase appeared

to break down to troilite. The steps in the reaction

could not be followed; they could involve reaction

with the surrounding matrix rather than straight

thermal decomposition.

Textural Features

In the "General Description" we distinguished

four distinct inclusion types. Each of these types

exhibits features that bear upon the preterrestrial

history of the whole meteorite.

TYPE 1 INCLUSIONS

This type of inclusion consists of (1) fragmental

pieces and single crystals of individual minerals

contained directly within the black matrix, and (2)

individual mineral phases that appear to have

grown within the black matrix. In the first category

the minerals are clearly debris that was incorporated into the matrix. In all, these debris fragments comprise approximately 8 vol. % of the

meteorite.

The majority of type 1 inclusions are in the first

category above, and are represented by euhedral

and angular olivines, angular pyroxenes, angular

chromites, and angular pieces of glass. Minerals

in the second category are calcite, gypsum, magnetite, and the two poorly characterized phases noted

earlier.

The olivines and pyroxenes vary in composition

from grain to grain, and a small percentage of the

olivines are moderately to strongly zoned. A microprobe grain count of the homogeneous (i.e., unzoned) olivine and pyroxene fragments indicates a

ratio of olivine to pyroxene of approximately 2/1.

The olivine fragments average larger in size than

the pyroxenes so the actual volume ratio will be

larger than this. Histograms of these olivine and

pyroxene compositions are given in Figure 10. The

diagrams are closely similar to the ones determined

by Fredriksson and Keil (1964) for the Murray

meteorite. Wood (1967a) made an extensive survey of this kind for all inclusions in ten C2

chondrites. He discussed some subtleties in the distribution from one meteorite to another; however,

the overall patterns are the same as for Murchison.

Figure 11 illustrates a special grain to grain survey that was made on an unusually metal-rich

section. Grains of olivine not associated with grains

of metal show the same kind of histogram as just

discussed above. Olivines associated with metal,

however, show an absence of fayalitic compositions.

Fredriksson and Keil (1964) suggested for the Murray C2 meteorite that metal was formed by a Prior's

Rule—type of process by reduction of the fayalitic

component of olivine to form metal and the more

forsteritic olivine. As compelling as this argument
20 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

is, it meets with some serious mass balance problems. In Murchison, for example, a fayalitic olivine

of 30-40% Fa contains about 0.1% NiO (Figure

18, and "Nickel in Olivines"). Reduction of the

FeO and NiO from this olivine would yield associated metal containing only 0.4% Ni, which is

over an order of magnitude smaller than that observed in any C2 meteorite (Wood, 1967). Metal

in Murchison, for example, ranges from 4% to 7%

nickel. Thus, the nickel balance does not work

out. In addition, the ratio of masses of metal to

forsterite in associated grains shows wide variation

with, in extreme cases, grains consisting of up to

50% (by vol.) of metal. It appears that reduction

in situ does not account for the metal-olivine assoOLIVINES

o

o

E

3

5

0

10

0

20

10

0

30

20

10

0

0

ciations. It would appear more likely that they are

the result of the initial condensation process from

the solar nebula. As will be discussed in the summary, depending on the total (hydrogen) pressure,

metal condensation accompanies or slightly precedes the condensation of the first forsteritic olivine. Thus, metal grains would be associated with,

and possibly acting as nuclei for, the precipitation

of forsterite. As condensation continues metal

ceases to form, while small amounts of more fayalitic olivine, not associated with metal, condenses.

Fragments of zoned olivines were found that

showed zonal variations from as little as 5 mole

% Fa to as much as 40 mole % Fa. It should be

noted, however, these results are largely from fragPYROXENES

ISOLATED GRAINS in C3 INCLUSION

CLUSTERED GRAINS in C3 INCLUSION

GRAINS in MURCHISON CHONDRULES

ISOLATED GRAINS in MURCHISON MATRIX

10 20 30 40 50

 58 0 10 20

Mole % Fe2Si04 | Mole % FeSiO3

FIGURE 10.—Histograms of olivine and pyroxene compositions. A few more Fe-rich compositions

(up to Fags) are omitted for brevity.
NUMBER 10 21

ments so that it is impossible to determine what

is rim and what is core, or indeed if the full variation of the original crystal is represented in the

fragment that was encountered. In many cases

fayalite values did not show a concentric arrangement but a monotonic change from one Mg-rich

edge across the fragment to the opposite Fe-rich

edge. Such asymmetric changes show that Fe-rich

edges cannot be the result of interaction with the

high iron matrix material. In some instances, however, concentric symmetry was observed with a

Mg-rich center and Fe-rich rims. In a few rare cases

reverse zoning was observed, with cores more Ferich than the rims!

One of the striking features observed in this type

OLIVINES

of inclusion is the presence of rare whole single

crystals of olivine in the matrix (Figure 12). In

many instances these crystals are perfectly euhedral,

showing a full set of terminating faces. They range

in size from 0.3 mm to f mm and are either equant

in shape or somewhat flattened prisms. This is, as

far as we know, the first reported occurrence of this

phenomenon in any C2 chondrite. Specimens of

Murray and Cold Bokkeveld we examined, however, exhibited the same kinds of olivine crystals.

It may be this is a characteristic feature of other

C2 chondrites. In some instances, otherwise perfect

crystals are broken or chipped. The crystals are

never attached to other grains but are isolated in

the matrix such that their removal leaves behind a

PYROXENES

-O

30

20

10

0

40

30

20

10 -

0

GRAINS ASSOCIATED WITH METAL

GRAINS NOT ASSOCIATED WITH METAL

10 20 30 40

Mole % Fe2Si04

50 580 10 20

Mole % FeSiO3

FIGURE 11.—Histograms of olivine and pyroxene compositions in Murchison. These data were

obtained on a metal-rich section different from that used for Figure 10.
22 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

FIGURE 12.—Euhedral olivine crystal (0.5 mm) embedded in

matrix.

smooth-walled negative crystal cavity. An interesting feature of these crystals is that the faces always

appear slightly frosted.

Some of these crystals are zoned. Measurements

of four of them showed core to rim values from Fa

25 to Fa 45, 3 to 8, 22 to 31, and 23 to 35. Other

crystals, however, were unzoned and showed consistent compositions of less than Fa 1. Of the

crystals that were selected for microprobe work and

study a few contained internal blebs of glass (up

to 36 microns), spherules of metal, and euhedral

crystals of spinel. These glass inclusions were described in detail under "Glasses."

It is clear these euhedral crystals did not form

within the matrix. Olivine is not a mineral that

develops crystal faces against impeding matrix as

do minerals like staurolite and garnet. Euhedral

olivines are found in terrestrial rocks only in instances where they crystallize within a melt (e.g.,

magnesian olivines poikilitically contained in pyroxene or plagioclase in some basalts, troctolite, or

peridotites) or subhedral crystals projecting into

open cavities (as fayalitic olivines in some volcanic

obsidians and trachytes, or coarse gabbro pegmatites). Furthermore, some of the fragments of olivine within the Murchison matrix show several

crystal faces still present on them. These were

originally fully euhedral crystals that were broken

and then incorporated into the black matrix. We

believe it highly likely that all of the angular

olivine fragments (most of which show no crystal

faces) are pieces of larger, once euhedral, crystals.

Only a small percentage of the olivine crystals managed to be incorporated into the Murchison matrix

before being fragmented.

Single crystal X-ray patterns made of these

euhedral olivines are extremely sharp, indicative of

a high degree of order and, by inference, relatively

slow cooling. They are clearly not quench products.

TYPE 2 INCLUSIONS

The most prominent inclusions in Murchison are

these so-called "white inclusions." Because they

tend to be rounded in outline, they are frequently

called "chondrules" by casual observers. Closer

study, however, clearly distinguished them from

true chondrules, and the presence of true chondrules in Murchison (type 3 inclusions) further

accentuates the distinction.

"White" is somewhat of a misnomer. The great

majority of the inclusions are snow-white, however, a few are blue or spinach green. Type 2 inclusions range in size from approximately 0.5 mm

to 4.5 mm and are generally rounded to elliptical

in cross section, though a high proportion of them

have intricate, crenulated or lobate outlines (Figure 13). In a few hand specimens we observed a

large number of elongated lenslike shapes that

showed a slight lineation pattern suggestive of solid

flow.

The boundaries of type 2 inclusions are generally sharp, although on a fine scale grains at the

edges jut out into the black matrix. Often the

matrix rimming an inclusion is unusually black

and fine grained. In no case is it possible to work

loose one of these inclusions from the matrix and

remove it as a whole unit, as can be done with true

chondrules.

Most of the type 2 inclusions are quite granular

in texture, the grains being only loosely packed

together. A needle gently raked over the surface

of one easily produces a small pile of grains. Most

of these inclusions consist of clusters of anhedral to

subhedral grains of usually more than one phase.

The dominant phase is highly magnesian olivine

(Figure 10), and it is present in almost all of these

inclusions. In rare instances, however, inclusions

are found that contain no olivine at all.

The most common inclusion consists of sugary
NUMBER 10 23

FIGURE 13.—Typical white inclusions in matrix: a, inclusion

(1.7 mm wide) surrounded by a narrow band (0.2 mm wide)

of fine-grained, inclusion-free matrix; b, two white inclusions,

each is surrounded by a narrow band of fine-grained matrix.

Long dimension of oval-shaped inclusion is 1.7 mm; c, polished section showing granular white inclusion surrounded

by fine-grained matrix. Width of field is 1.5 mm.

textured, granular, white forsterite which may contain blebs of metal. Within a given inclusion the

forsterite shows some variations in composition

from grain to grain. The average variation we

have observed is from Fa 1 to Fa 5, although in a

few instances fayalite contents up to Fa 60 were

observed. Accessory spinel, calcite, diopside, troilite, pentlandite, whewellite, and chromite may be

present as intergranular phases in type 2 inclusions.

Some of these inclusions contain appreciable

amounts of low calcium pyroxene with the olivine,

and in some instances the pyroxene exceeds the

olivine. Other, less abundant, inclusions consist of

white forsterite laced through with flakes of the

spinach phase (layer-lattice silicate; see "Other

Layer-Lattice Silicate"). In a few cases such inclusions exhibited the peculiar, regular interleaved

olivine-spinach texture noted earlier, in which it is

possible to break the plates of olivine and spinach

from each other like separating pages of a book. A

small number of inclusions consisted entirely of

clusters of the spinach phase. We did not, however, observe a full range of proportions from all

olivine to all spinach. The spinach was, in all

cases, iron-rich (approximately 30% FeO), while

the coexisting olivine was generally iron-poor. It

is, therefore, not possible to derive the spinach* (a

mixture of polymorphs of chamosite ± serpentine)

from in situ hydration alteration of the olivine

without invoking an improbable sequence of cation additions and subtractions.

A very small number of white inclusions contained no olivine but consisted of spinel with calcite, or spinel with clinopyroxene. The former represented the largest sizes of white inclusions ever

seen in the meteorite, up to 4.5 mm across.

Finally, blue patches in white inclusions (approximately 0.15 mm), consisting mainly of hibonite, perovskite, and spinel with or without

diopside, were found in trace amounts. These high

temperature Ca-rich assemblages were described

and discussed in detail under "Hibonite" and

"Perovskite."

TYPE 3 INCLUSIONS (TRUE CHONDRULES)

True chondrules are in low abundance in Murchison. Because they do not break with the matrix,

it is relatively easy to distinguish them. They

stand out as spherical or ellipsoidal projections on
24 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

FIGURE 14.—Assorted true chondrules which were easily separated from matrix. Largest shown is 0.75 mm in diameter.

fresh fracture surfaces and can, with care, be

worked loose and removed (Figure 14). The majority of the chondrules are dark gray to black on

the outside, although in a few instances very small

(0.1 mm and smaller) pure white spheres occur in

the matrix.

The white spheres are mechanically weak and

break open at attempts to remove them from the

matrix. Internally they consist of very fine-grained,

silky white shreds of either clinoenstatite or orthoenstatite (almost iron-free) with minor olivine

and calcite sometimes present. X-ray patterns of

the orthoenstatites showed disordered or ordered

forms in individual instances (Pollack and Ruble,

1964).

The more common black chondrules ranged

from 0.05 to 0.8 mm in diameter. Separated individual ones were mounted and sectioned. These

consisted of a variety of internal textures and mineralogies. Mostly they contained olivine as granular aggregates of subhedral to anhedral grains

surrounded by streaks of glass, or stringers of the

spinach phase layer-lattice silicate. Small patches

of the poorly characterized (Fe-S-O) phase are peppered through some individual chondrules. Capoor pyroxene was found but is rare. A microprobe

survey of olivine and pyroxene compositions shows

most of the olivine to be close to pure forsterite

with a few more iron-rich compositions, and a small

peak at Fa 58—59 (Figure 10). This peak is due to

one single chondrule that contained this composition of olivine as scattered subhedral crystals within

a matrix of a pigeonitic pyroxene (approximately

Fs 50) that contains stringers of glass. Compositions

within individual chondrules were uniform.

Most chondrules contained some minor specks of

sulfide and metal, and few were quite rich in metal

with blebs of 50 to 150 microns. Individual metal

grains are uniform in composition, but the nickel

content did vary somewhat from grain to grain

within individual chondrules, from 4.5 to 5.7% Ni.

One chondrule contained a single metal grain that

ran 9.6% Ni.

Many of the chondrules contained from minor

to major amounts of irregular patches, blebs, and

streaks of glass that were quite variable in composition from point to point. Microprobe analyses

show it to be a high Ca-Al-silicate glass that is

alkali-poor. The compositions are all within the

range of values for the glass found in type 1 inclusions (Table 8).

Some unique chondrules were found. One consisted almost entirely of the poorly characterized

(Fe-S-O) phase discussed earlier. Another consisted of small subhedral to anhedral grains of

olivine (Fo 99) surrounded by massive spinach

layer-lattice phase (Table 2b). Once again it is

clear that the layer-lattice phase could not be derived by direct hydration alteration of virtually

Fe-free olivine because of the high iron content of

the layer-lattice mineral. Another chondrule was

seen that contained a fairly large, lobate void space

cavity. Small cavities were evident in several others; however, we could never be certain they had

not been created during the sectioning process by

the plucking out of small metal grains. The large

cavity, however, is an original feature by virtue of

its unique shape and size.

It is clear that the individual true chondrules

represent much of the same range of chemical conditions as observed in the types 1 and 2 inclusions

described earlier. One significant difference, however, is the smaller number of different mineral species found in the true chondrules in contrast to the

white inclusions, especially the very high temperature phases such as perovskite, hibonite, and spinel,

which were not observed in any true chondrule.
NUMBER 10 25

a

FIGURE 15.—C3 xenolithic inclusions in Murchison: a, largest fragment found is 1.3 cm in

diameter and is contained in an 18-cm piece of Murchison; b, close-up of same fragment (note

the thin separation of fragment from surrounding matrix); c, smaller (7 mm) xenolithic fragment of same C3 meteorite type found in another sample of Murchison.
26 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

FIGURE 16.—Polished section of C3 inclusion (type 4) shown

in Figure 156. All bright spots are troilite or pentlandite.

This unusually high-sulfide-containing inclusion is practically

metal free. Width of field is 1.5 mm.

It is significant that among the chondrules collected and studied from Murchison, not one is like

the common chondrules of the ordinary chondrites:

barred olivine, radiating pyroxene-plagioclase,

porphyritic olivine. Furthermore, the glass within

Murchison chondrules is very different in its range

of compositions from the sodium-rich glasses of the

chondrules in ordinary chondrites.

TYPE 4 INCLUSIONS (XENOLITHIC FRAGMENTS)

Within Murchison we encountered xenolithic

fragments of two other different meteorite types:

(1) six fragments of one meteorite type, ranging

from a few millimeters up to 13 mm (Figure 15);

and (2) a single fragment, 1.2 mm, of yet another

meteorite type (Figure 17).

C3 CHONDRITE INCLUSIONS.—Fragments of this

meteorite type are a distinctive light blue-gray

color. The largest fragment is slightly separated

from the surrounding matrix such that it could be

completely removed as a unit. Within these fragments we observed both distinct true chondrules

and inclusions, the latter with the same morphologies as the type 1 and type 2 inclusions found in

the body of Murchison proper.

The main matrix of these xenolithic pieces consists of finely comminuted, submicron size olivine

and pyroxene with numerous coarser irregular

patches of abundant troilite and pentlandite (Figure 16), and a trace of ilmenite and magnetite.

Nothing can be said about the matrix olivine and

pyroxene compositions; they are too fine-grained

for microprobe analyses.

Contained within this matrix were inclusions

that consisted of single phase angular fragments,

rounded pieces, anhedral, subhedral, and (rarely)

euhedral grains of mainly olivine, with lesser Capoor pyroxene. The only metal seen in any xenoFIGURE 17.—Second type of xenolithic inclusion in Murchison: a, inclusion shown in upper right is 1.2 mm in diameter

and contains large euhedral crystals of olivine (Fo100) in a

partially devitrified groundmass (note contrast in texture

with Murchison matrix) ; b, enlarged area of inclusion showing

devitrified glass groundmass. Large crystals are olivine, small

euhedral crystal is chromite (lighter gray), bright spots are

metal and sulfide. Scale bar is 100 microns.
NUMBER 10 27

lithic fragment occurred as two micron-size grains

in an olivine inclusion.

In addition, inclusions of multigrained aggregates of olivine, pyroxene, minor sulfide, and a

minor unidentified phase were found. All of these

inclusions appear analogous to the type 1 and type

2 inclusions seen in Murchison proper.

The olivines and pyroxenes in these xenolithic

fragments show wide compositional variations from

grain to grain with, however, a different distribution of compositions than in Murchison proper

(Figure 10). Many of the grains are zoned. Olivine

zones ranged from Fa 2-20 to Fa 51-57, with all

combinations of values between. Pyroxenes ranged

from Fs 2-8 to Fs 15-22, with other values in between.

Most of the inclusions in the xenolithic fragments were rimmed by nonopaque, ultra finegrained matrix (of submicron olivine and

pyroxene) that is virtually free of sulfides and

coarser grained silicate fragments.

True chondrules are present in the xenolithic

fragments; however, they are rare. Only a few

were observed on the largest fragment. No detailed

study was made of them.

It is worthwhile to highlight the complete absence of any layer-lattice silicate in the xenolithic

meteorite fragments. At the contacts of the fragments with the surrounding Murchison matrix

there is a complete break, with no interfingering of

layer-lattice material into xenolithic fragments.

Thus it is impossible that the hydrated layer-lattice

phases in Murchison proper are derived from the

alteration of olivine in situ. If that were the case

then the olivines in the xenolithic fragments

would have been pervasively altered also, or at least

attacked at their rims in contact with Murchison

proper. The very smallest xenolithic fragments

(approximately 1 mm) show just as sharp boundaries with the black matrix of Murchison as do

the larger ones.

In addition, the xenoliths contain no other low

temperature phases like those observed in the surrounding Murchison proper: calcite, whewellite,

gypsum, poorly characterized phases.

Macroscopically these appear to be xenoliths of

a C3 chondrite. Comparisons were made with specimens of a number of C3s, of both the Ornans and

Vigarano subtypes (Van Schmus, 1969). In general

appearance the fragments looked more like the

Ornans subtype; however, the very high ratio of

matrix to inclusions plus chondrules and the nonopacity of the matrix material contrast markedly

with the Ornans-subtype as examined by us directly

and as described and characterized by Van Schmus.

Furthermore the almost complete absence of

metal, and the abundance of sulfides adds to the

problem of comparison. Sulfides make up about 7

vol. %, half of which was troilite and the other

half pentlandite.

A partial wet chemical analysis was performed:

Mg = 14.5%, Fe = 25.2%, Ni = 1.55%. Mason

(1971) noted some chemical groupings of Vigarano

and Ornans subtypes on a plot of Mg against Fe.

A plot of the values given above lies exactly between the two groupings as illustrated in Mason's

paper. On this basis it is not possible to put it

distinctly into either group.

In the histograms of olivine compositional variations for C3 subtypes presented by Van Schmus

(1969), these xenolithic fragments (Figure 10)

show their main peak at 5-10 mole % Fa, which is

similar to the Kainsaz meteorite in the Ornans

subtype group.

We conclude that the xenolithic fragments in

Murchison are of a C3 chondrite that is similar to

the Ornans subtype in terms of olivine-pyroxene

compositional distribution, is intermediate between

the Ornans and Vigarano subtypes in terms of the

bulk composition, and is unlike either subtype in

terms of texture.

G. Mueller (1966) noted the presence of an angular xenolithic inclusion in Mighei C2 chondrite.

Megascopically it appeared similar to a C3 chondrite. It was, however, a darker colored fragment

and contrasted less markedly with the surrounding

Mighei matrix than the fragments in Murchison

(G. Mueller, pers. comm,). It is possible that C3

inclusions in C2 meteorites is more widespread

than heretofore imagined.

XENOLITH OF UNKNOWN METEORITE TYPE.—One

section of Murchison contains a single small (1.2

mm) xenolithic fragment of a second meteorite type

(Figure 17). It consists of blocky, jointed pieces

(some subhedral crystals) of pure forsterite set in

a matrix of glass, with traces of troilite, metal, and

euhedral chromite. The glass is partially devitrified

into a dendritic pattern of submicron needles.

In texture and mineralogy this fragment is identical to a unique chondrule observed and photo-
28 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

graphed by Ramdohr (1966) in the Adelie Land

ordinary chondrite (L5). He referred to it as an

"unknown (or nearly so) type" of chondrule. This

occurrence in Murchison may be a fragment of this

rare type of chondrule.

all zones regardless of fayalite content. As an example, CaO = 0.26% as fayalite goes from 36 to

48. Fredriksson and Keil (1964) observed no CaOfayalite correlation in olivines of the Murray C2

chondrite.

Mineralogical-Compositional Relationships

In studying the Murchison meteorite a number

of relationships were observed between mineral

phases and between compositional components of

individual mineral phases, which bear on the history of the meteorite.

CALCIUM IN OLIVINES

Weight percent CaO was obtained for a group

of 21 olivines, of which 17 were homogeneous and

4 were zoned. These were chosen at random and

included olivines in both type 1 and type 2 inclusions. Fayalite contents ranged from 0 to 85,

with a distribution like that shown in Figure 10.

CaO contents ranged from 0.08 to 0.77%. No correlation exists between CaO and fayalite contents

for the homogeneous olivine grains. For the zoned

olivines one crystal showed a positive correlation:

CaO increased from 0.15 to 0.48% as fayalite content increased from 54 to 85. The other zoned

crystals, however, show constant CaO contents in

CHROMIUM IN OLIVINES

Twelve random olivines (9 homogeneous, 3

zoned) were analyzed for Cr2O3 values. These

ranged from 0.06 to 0.3 wt. %. Homogeneous olivines showed no correlation between chromium

and fayalite contents. Similarly, chromium remained constant across all zones in zoned crystals

(e.g., Cr2O3 = 0.3% for fayalite from 25 to 35).

MANGANESE IN OLIVINES

Thirteen random olivines (9 homogeneous, 4

zoned) were analyzed for MnO. These ranged from

zero to 0.3 wt. %. Although there was a slight

tendency for MnO to increase with fayalite content, the data were too few to draw a definite conelusion. Such a correlation would be likely because

of the closely similar behavior of iron and manganese in most sets of conditions. Terrestrial (crustal)

and most meteoritic conditions would not be expected to show any substantial difference in this

trend (Simkin and Smith, 1970).

0.20-

0.1 5 -

0.10 -

0.05 -

20 30 40

Mo I. % Fayalite

50 60 70

FIGURE 18.—NiO vs fayalite content in olivine grains in Murchison.
NUMBER 10

29

NICKEL IN OLIVINES

Nickel analyses were performed on 31 olivines

randomly selected from one polished section o£

Murchison (Figure 18). A correlation exists: NiO

increases with the fayalite content. As fayalite goes

from essentially zero to 80 mole percent, NiO goes

from less than 50 ppm up to 2300 ppm. There is

some scatter to the data, part of which is analytical

error, and a smaller portion of which is due to errors in always returning to the same grain to analyze for both Fe and Ni, since both were done on

the same microprobe spectrometer channel, with all

the Fe counts obtained first. The correlation is,

nevertheless, quite evident and is exactly opposite

to the correlation observed in terrestrial rocks by

Simkin and Smith (1970).

The explanation of the opposite correlation is

clear from the calculations of R. Mueller (1965) in

the system Fe-MgO-SiO2-O2. In terrestrial rocks, olivines (and coexisting pyroxenes) coexist at equilibrium with ferrite phases such as magnetites or

chromites but not metal. With increasing oxidation state the fayalite content of the olivine decreases as iron is oxidized from the + 2 to the + 3

state into ferrite phases. Since the oxidation potential of nickel beyond the +2 state is extremely

high it becomes progressively enriched in the olivine in which it forms an ideal solid solution

(Campbell and Roeder, 1968). Thus, Mg-rich terrestrial olivines contain more NiO as observed by

Simkin and Smith (1970).

In a more reducing environment than the terrestrial crust, at oxygen partial pressures less than

those of the ferrite-metal boundary, just the reverse

happens. With decreasing oxidation state the fayalite content of the olivine (and pyroxene) decreases

as iron is reduced into the metallic state (or a reduced sulfide phase such as troilite). Because the

oxidation potential of nickel from the +2 state to

the neutral state is higher than that of iron (from

+2 to neutral), nickel is more readily reduced than

iron. Thus, for oxidation states that do reduce

iron, nickel is reduced along with it. As the oxidation state drops the olivine becomes more Mg-rich

and poorer simultaneously in nickel.

It is clear from studies on equilibrated chondrites that the fayalite content decreases with lower

oxidation state and that Mg-rich (Ni-poor) silicates,

such as olivines and pyroxenes in iron meteorites,

TABLE 9. Equilibrium condensation sequence of phases observed in Murchison (total pressure 10-* atm) *

Phase

Hibonite

Perovskite

Spinel

Metal

Diopsi de

Fors ten' te

Ertstati te

Intermediate compositions

of olivines and pyroxenes

Troilite (+ pentlandite)

Hagneti te

Layer-lattice phases

Poorly-characterized phases

Whewel1i te

Calci te

T°C (rounded values)

1500 (approx. )

1375

1240

1200

1180

1170

1075

700-250

425

130

<150

«1 00

<<100

<<1 00

Most data after Grossman, 1972. Temperatures of phases

condensing below 150°C (except magnetite) are estimated

by the authors.

olivines in pallasites, and pyroxenes (and rare

olivine) in enstatite chondrites and enstatite achondrites, represent reduced environments (and

generally higher temperature environments than

more oxidized meteorites). The olivine and pyroxene fragments found in the matrix of Murchison clearly did not originate there in equilibrium

with each other (because of the large grain to

grain variations in composition, and the clastic texture of these inclusions). They represent a variety

of oxidation conditions. By virtue of the correlation we observe (Figure 18) these conditions were

established in equilibrium with metal and not in

equilibrium with the ferrite phases which occur in

small amounts also in the matrix and inclusions of

Murchison. On the basis of the kind of condensation sequence which formed the minerals of Murchison, metal and olivine formed closely together

in temperature, while ferrites formed about 1000°C

lower. This condensation sequence will be discussed in detail in the summary (also cf. Table 9).

Figure 19 is a plot of the NiO content in olivines

from one of the xenolithic fragments of the C3

chondrite found in Murchison. It shows the same

trend as for Murchison proper. From our earlier

description (C3 Chondrite Inclusions) this meteorite is also disequilibrated and clastic-textured. The

almost complete absence of metal and the high

amounts of troilite and pentlandite indicates it is
30 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

0.20

O 0.15

0.10

0.05

• •••—•-

10 20 30 4 0 50 60

Mo I. % Foyolite

FIGURE 19.—NiO vs fayalite content in olivine grains in C3 xenolithic inclusion.

70

an agglomeration of grains from a higher sulfur

environment than for Murchison proper. Thus,

most of the iron and nickel reduced out of the silicate phases (for the Mg-rich reduced compositions,

which dominate the histogram, Figure 10) went

into iron and nickel-rich sulfide phases.

NICKEL IN PYROXENES

In doing the survey of NiO in olivines of Murchison, pyroxene grains were also examined. No detectable NiO was found in any of them. This is

logical in view of the histogram (Figure 10): virtually all the pyroxenes are very Mg-rich, hence

very reduced and thereby Ni-poor.

CHROMIUM AND PHOSPHORUS IN METAL

The high Cr and P contents of the metal grains

are different from all known meteoritic metal analyzed thus far. It is similar to some of the metal

grains from the lunar samples, though they never

reach the values observed in Murchison metal. Superficially it would appear that the metal represents

somewhat more reducing conditions than for other

meteorites, and that Cr and P were alloyed into

early-forming metal rather than coming out in

lower temperature Fe- and Cr-rich spinels and silicates, and phosphates, respectively. Certainly the fact

that almost all the metal occurs as included beads

within very iron-poor olivine would tend to bear

this out. On the other hand, the metal shows no

detectable Mn or Si. The latter would require extreme reduction such as observed in the Horse

Creek iron or in the enstatite chondrites. Mn, however, would be expected to be reduced into the

metal along with Cr and P. Its solar abundance

(Goles, 1969) relative to Fe is about the same as P

and is only a factor of two less than Cr. In this

regard, metal in enstatite chondrites (Keil, 1968),

though notably high in Si, shows no Cr or P of

unusual significance. We are currently investigating the metal in a large sampling of carbonaceous

chondrites and hope to be able to draw conclusions

in a later paper. For the time being we have no

solution to the unusual compositions of the metal

grains in Murchison.

MINERALS NOT PRESENT IN MURCHISON

Perhaps as significant as the minerals that have

been found is the absence, or only trace presence,

of minerals common to the ordinary chondrites:

plagioclase feldspar, chromite, ilmenite, or phosphates such as whitlockite. All sections of Murchison were searched carefully for these and only

chromite was found in traces. Ilmenite was found
NUMBER 10 31

as a trace within one of the C3 xenolithic inclusions, but not in Murchison proper.

Wet Chemical Analysis of Murchison

As in overall appearance, so too in bulk chemical

composition, Murchison is closely similar to Murray. The results obtained are shown in Table la

and compared with the published data of Jarosewich (1971). These data are also compared on a

volatile-free (C, H, N, O, S) basis in Table lb. On

this basis the agreement between the major constituents is better since the effect of our larger

H2O (-) value is eliminated. Jarosewich has kindly

supplied a sample of his analyzed material to allow

for a comparison of some of the analytical results

(especially Na and Fe) on the sample. These data

follow:

SiO2

Fe (total)

MgO

Na2O

H2O (total)

C (total)

Jarosewicli

29.07

22.15

22.29

19.94

0.23

10.05

2.12

this work

28.95

21.73

21.73

19.94

20.01

0.21 (flame emission)

0.21 (atomic-absorption)

9.66

1.96

Analysis by Jarosewich of two separate portions

of our sample confirmed our high Na value. We

have further investigated this point by determining

Na in five separate interior fragments from five different pieces of Murchison and found that the

Na2O content ranged from 0.19% to 0.71%. The

weighted average was 0.48%. Sodium in our analyzed sample is relatively high and variable. Such

a result could be due to contamination after fall

or to the fact that sodium is indeed heterogeneously

distributed in this meteorite.

We have not assigned values for FeS, FeO, and

Fe2O:{ in our analysis for the following reasons:

1. Sulfide sulfur is estimated by subtracting the

sum of elemental and sulfate sulfur from the total

sulfur content. There is a tendency for both the

elemental and sulfate sulfur values to be low due

to incomplete extraction of the elemental sulfur

by carbon tetrachloride or of sulfate sulfur by hot

water. This results in a high estimate of sulfide

sulfur.

2. As described earlier an appreciable amount of

sulfur is present as the so-called poorly characterized Fe-S-O phase, rather than as FeS. Also some

sulfur is present as pentlandite.

3. Mineralogical examination by point-counting

on polished sections shows that the total sulfide

content is much less than that calculated by subtracting elemental and sulfate sulfur from the total

sulfur. Point-counting of four sections gives troilite

+ pentlandite ranging from 0.07% to 0.23% by

weight (average 0.13%).

4. Earlier, in the discussion of the layer-lattice

matrix material, crystal-chemical considerations indicated an appreciable amount of ferric iron in the

matrix other than that due to the minute amount

of magnetite. These facts, along with the inherent

errors in the estimate of FeS make the assignment

of iron as FeO difficult.

Summary and Discussion of Observations

Many of the foregoing observations bear out

what has been described in C2 meteorites by others

(DuFresne and Anders, 1962; Wood, 1967; Mason,

1962-63 and 1971). Some of the observations, however, are new and raise questions regarding interpretation and how they fit into existing schemes of

carbonaceous chondrite genesis. Four of these will

be summarized and discussed in this section.

First, it has been recognized for some time that

C2 meteorites possess a high temperature fraction

contained in a matrix of low temperature material.

The high temperature fraction is generally considered to be forsterite with some enstatite and spinel.

In addition to this assemblage we have observed

two other high temperature fractions: the perovskite-hibonite-spinel-(±)diopside assemblage; and

blebs of Ca-Al-silicate glasses, of variable compositions, contained within olivine (and occasional

spinel) crystals.

The perovskite-hibonite-spinel-(±)diopside assemblage is closely similar to the assemblage observed in some C3 chondrites (Fuchs, 1971; Keil

and Fuchs, 1971); in contrast to them, however, no

gehlenite or anorthite was found. In Murchison

the assemblage is very rare and is not found with

the frequency it is in such C3s as Allende. The

fact that it is present at all in a C2 is significant,

and together with the glasses it provides a partial

answer to the question raised by Mason (1971) re-
32 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

garding the mineralogical form of Ca and Al in

C2 meteorites.

The sequence of direct condensation of crystalline solids from a solar nebula was originally computed by Lord (1965), later recomputed by Larimer

(1967), and most recently recalculated with a revised scheme by Grossman (1972). Because of the

lack of thermodynamic data on hibonite no calculation includes it in the crystallization sequence,

although an educated guess would place its stability in the 1350°-1450°C range (Grossman, 1972).

In Grossman's calculation, at a total gas (primarily

hydrogen) pressure of 10'3 atm, perovskite condenses out at 1374°C, followed by melilite and

spinel at 1352°C and 1240°C, respectively. Melilite

does not occur in Murchison; however, the association of diopside with spinel could represent the

breakdown products of melilite by later reaction

with gas at 1177°C, or the bypassing (metastably)

of the melilite field. Forsterite and enstatite do not

appear until 1171°C and 1076°C, respectively.

Thus, the perovskite-hibonite-spinel-(±) diopside

assemblage, though minor in quantity, clearly represents a higher temperature stage than heretofore

observed in any C2 meteorite. It may actually occur in other C2s, but not yet recognized.

Whether metal precedes, accompanies, or follows

the condensation of forsterite depends on variations

in the total (hydrogen) pressure, with less than an

order of magnitude controlling the sequence

(Grossman, 1972). In Murchison, most of the metal

occurs within olivine crystals, indicating pressures

above 104 atm where the metal condenses before

forsterite. The euhedral morphology (cf. Textural

Features) of many of the forsterite crystals suggests condensation from a vapor phase. Metal

grains must have acted as preferred nucleation sites

for some of the olivine because the high surface

tension of metal surfaces makes them ideal nuclei.

The few zoned olivines represent disequilibrium

with the gas with falling temperature.

The form of the metal grains within olivine

crystals is always spherical or subspherical blebs,

or lobate clusters of two or more blebs. The shapes

strongly suggest the metal was originally present

in liquid drops. This has also been noted by Wood

(1967b), who drew the same conclusion. The shapes

contrast sharply with the angular metal grains

and occasionally stringy metal veins of the ordinary

chondrites. In experimental systems iron condensed

from the gas phase usually forms elongate crystals

and needles. The textural suggestion of a liquid

phase for the metal in Murchison is further raised

by the Ca-Al-silicate glass inclusions that are relatively abundant within olivines (and some spinels).

As noted in "Glasses" under "Mineralogy," these

glass bleb inclusions vary in composition and occasionally contain void space bubbles (Table 8,

Figure 7). In one instance a single bleb was found

that consisted of two glasses of different compositions. Compositionally, the average glass computes

to normative anorthite and diopside with excess

silica. In a solar nebula condensation (at 103 atm

total pressure) crystalline anorthite should condense

out at 1089°C, after forsterite, but before enstatite.

The mineral anorthite readily crystalizes in experimental systems and does occur in the high temperature fraction of some C3 chondrites, as well as in

euhedral to subhedral crystals in some achondrites.

The presence of glasses of these compositions

within olivines and some spinels in Murchison

points to an early liquid stage. As discussed in the

section on glasses, one possibility is that the glass

inclusions represent trapped blebs of a coexisting

rest-magma from some magmatic stage in a planetary object. We noted there, however, four major

difficulties with postulating a magmatic state that

requires complicated, highly contrived conditions

that are contrary to the primitiveness of a meteoritic object such as Murchison. It appears more

reasonable to suggest that these glasses are part of

the normal formational processes that condensed

primitive solid matter in the solar system, as many

others have suggested (e.g., Anders, 1971), rather

than a magmatic stage on some early planetary

object.

The variability in the compositions of the glass

blebs clearly indicates that they were not formed

in a single event, or stage, sampling a homogeneous

solar nebular composition.

The distinct indication of a liquid phase raises

the question whether the spherical habit of the

metal grains in olivines might also represent original liquid drops. Since liquid metals cannot be

quenched to glasses, as can most silicate liquids,

there is no way to decide other than to point to

the morphology.

Wood (1963) raised the question of condensation
NUMBER 10 33

of solar nebular matter initially into a liquid stage.

The idea was generally discarded when it became

clear that unreasonably high total pressures would

be required for the solar nebular gas, of the order

of 10 to 103 atmospheres (Anders, 1971). Recently,

however, Turekian and Clark (1969) have invoked

total pressures in the range of 0.1 to 1 atm as a

means of accounting for density differences and

differences in accretion histories among the terrestrial planets, Mercury, Earth, and Mars. Toward

the center of the primitive solar nebula both pressure and temperature would increase (Cameron,

1962).

Although two of the glasses in Murchison reach

7.5% and 9.4% MgO, they are all much too depleted in it. Thus, they are fractionated relative to

nebular abundances. Formation of liquids of these

compositions at pressures of 1 atm or more would

require temperatures in the range of 1350-1450°C,

as noted under "Glasses." In a condensation of

these liquids from the solar nebular gas they may

be the compositions that liquefy first. With activity

data for the elements in liquids in these compositional ranges, a calculation of the first liquid

composition to condense is possible. Such calculations are currently in progress by M. Blander

(personal communication).

The most logical sequence to account for these

glasses, as well as the apparent initial liquid droplets of metal, would be for direct condensation of

liquids near the center of the solar nebula, at

pressures and temperatures commensurate with

the formation of silicate and metal liquids. Turbulent conditions and solar-flare activity could cause

variation in the compositions of small regions of

space as well as the necessary fluctuations in pressures to cause liquids to form. The majority of

these drops did not survive but, with falling pressure, were resorbed into the gas phase. Some very

small droplets did survive, however, and were

moved outward in the ecliptic plane. There, with

falling pressure and temperature, additional resorption into the gas phase would occur until the

droplets became cool enough to act essentially as

solids, or at least develop a surface skin that would

inhibit reevaporation. Hoyle (1960) described the

process of separation of an ecliptic plane disk of

matter from the proto-sun, and the transfer of

angular momentum to it. He calculated that early

condensed matter could easily migrate outward

away from the inner part of the disk, as long as the

condensed matter does not accrete into objects

above 100 cm in diameter.

Thus, these tiny quenched drops could move outward into less turbulent regions where, Hoyle estimates, the average pressure of matter in the gaseous

disk is 10"3 atm. Here the droplets that survive become incorporated into the dominant early condensing solids, forsterite and spinel.

Attractive as this scheme is, it still requires at

least transient pressures of above 100 atm, held

long enough to allow some droplets to condense. In

addition, as noted under "Glasses," some of the

liquid blebs are deformed from spherical shapes

and consist of elongated blebs that lie parallel to

crystallographic directions in the olivine crystals

in which they are contained. This would mean that

the glass drops would have to remain plastic and

deformable while the temperature fell 200°C (from

approximately 1350°C, where the glasses condense,

to 1170°C at which forsterite sublimes), and the

pressure fell five to six orders of magnitude (102 or

103 down to 10-3 atm).

An alternative scheme would be for the earliest

crystalline phases, like perovskite, melilite, spinel,

hibonite, diopside, to condense from the solar

nebula at equilibrium gas pressures of 103 atm,

and then suffer a high transient heat, such as suggested by Whipple (1966) and Cameron (1966).

This would melt the particles already condensed,

and they would quench to a metastable state as

glass droplets, later to be incorporated into olivine

once the normal sequence of equilibrium condensation resumed. The major problem with this scheme

is that no combination of solids that condense from

the solar gas at temperatures above that at which

forsterite condenses can form glasses of the compositions that were measured (Table 8). The silica

content is plainly too high.

This leads us to the interesting approach of

Blander and Katz (1967), in which they established

an argument that the kinetics of nucleation processes favor the metastable nucleation of liquid

drops initially, at pressures of 103 to 104 atm.

These would form by supersaturation of the nebular gas, component by component, as subcooling

took place below the temperatures where equilibrium solids should have crystallized out. Under such
34 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

a regime, variability in compositions among the

droplets of liquid would be a direct consequence.

Furthermore, droplets formed by such a nonequilibrium process could maintain their plasticity,

stiffening only when they survive to lower temperatures (i.e., below the glass transition temperature).

As such, they could become nuclei for forsterite and

spinel that later crystallized via equilibrium condensation from the gas, and in individual cases still

be plastic enough to become crystallographically

elongated within the forming olivine. Under conditions of supersaturation, metal would be expected to form spherical to subspherical grains

also; this would happen even if the metal condensed directly to a solid state. Blander (personal

communication) states that iron vapor can be subcooled as much as 300°C before condensation.

This treatment of Blander and Katz offers many

attractive advantages in explaining these glasses

in Murchison. The only disadvantage is the lack

of quantitative thermodynamic data for the liquids

at the present time. For the supersaturation condensation process to work for Murchison, about 100

to 200°C (at 103 atm) of subcooling would be required. Blander (personal communication) believes

this amount is probable in this process.

Second, details of the accretion process are, of

course, matters of interest and speculation. We

observed that the white (type 2) inclusions are

almost always surrounded by thin rims of exceptionally black matrix material (Figure 13). The

deep blackness is due to the complete absence of light-colored grains of olivine, pyroxene,

etc. These inclusions typically do not have a great

deal of mechanical integrity, as noted earlier. They

appear to have clumped together into commonly

ellipsoidal, but occasionally irregular, masses before incorporation into the accreting Murchison

parent body. The low temperature, submicron size

(smoke) layer-lattice material appears to have

coated the white masses forming the thin, black

rim. In a hard vacuum, surface-attractive forces of

newly formed layer-lattice phases, with high surface

area per unit mass, would be quite "sticky." The

formation of the adhering film of layer-lattice material would act to seal each clump of coarser

grained silicates and allow each of them to act

as a unit until incorporation into the accreting

body. Even at that the low mechanical integrity of

the white (type 2) inclusions shows that the accretion process for the parent body of Murchison must

have been an exceedingly gentle process; clumps

of silicates, smoke-size layer-lattice particles, true

chondrules, single crystal grains and grain fragments, and fragments of at least one other body

(type 4 xenolithic inclusions) must have^been moving with near zero relative velocities, otherwise the

white inclusions would never have survived. Indeed, the single grains of silicates in the matrix

(type 1 inclusions) may be, in part, the remains of

white clusters that were disaggregated in the accretion process.

Third, it is worthwhile to reemphasize our observation of the peculiar form of green (spinach)

layer-lattice silicate that occurs as regular interleaved plates within forsterite grains (described

under "Other Layer-Lattice Silicate" and "Type 3

inclusions") (Figure 3). It should be noted that these

easily separable green plates are not connected to

the exterior black matrix material. DuFresne and

Anders (1962) observed this spinach phase within

olivine in Murray and from it concluded that olivine was pervasively altered by hydration, and these

represented the process caught short of completion.

As we have shown in great detail earlier the

layer-lattice phase (or phases) is not a simple

chemically hydrated equivalent of olivine. In addition, we wish to emphasize here the importance of

the type 4 inclusions (xenolithic fragments). These

fragments were clearly derived from other accreted

objects that were fragmented, dispersed, and later

incorporated into the Murchison body. If pervasive

hydration-alteration then attacked almost all of the

Murchison olivine to form the layer-lattice material,

these olivine-rich xenolithic inclusions should have

been altered also; they are not. In addition, Onuma

et al. (1972) on the basis of his oxygen isotope

work found "no direct genetic relationship between

any pair of the three fractions: matrix [i.e., layerlattice material], high-iron olivine, and low-iron

olivine." Clearly, the layer-lattice material formed

in space as a low temperature condensate at under

150°C (Anders, 1971; Onuma et al., 197,2) and

accreted into a body, accompanied by high temperature mineral fragments and xenolithic fragments.

The development of the green plates of spinach

within olivine may be related to strings of elongated glass blebs arranged in parallel rows within
NUMBER 10 35

condensed olivine crystals. It these glasses were

considerably more Mg- and Fe-rich, and Ca- and Alpoor, than the glasses discussed earlier they could

have been attacked at low temperatures (below

150°C) when the fine, smoke-size particles of layerlattice matrix material were condensing. Water

was the major oxygen-bearing, gas-phase component, and it preferentially attacked these glass

layers within olivine. Such Mg- and Fe-rich, Caand Al-poor glasses would have formed at somewhat

lower temperatures than the other glasses that did

survive within olivine crystals. It is, in our opinion,

highly unsatisfactory to postulate the existence of

a glass that is now completely destroyed in order

to account for the peculiar olivine-spinach texture

shown in Figure 3. Nevertheless, it is clear that the

textural relation between high temperature olivine

and the low temperature, layer-lattice spinach

phase, together within single grains, must precede

the accretion of the host olivine into the parent

body. We have shown earlier that the alteration

could not have taken place after accretion, otherwise other olivines, both in the matrix and in the

xenolithic inclusions, would have been altered

also.

Fourth, by whatever process the mineral

components of Murchison condensed (i.e., by

equilibrium condensation or by nonequilibrium

subcooling-supersaturation-condensation), there was

a more or less continuous fractionation of mineral

phases as the nebular gas temperature fell. If we

use the equilibrium condensation model (as computed by Grossman, 1972) plus estimates from

other sources (e.g., Onuma et al., 1972) as bases

for comparison only, then the estimated range of

temperatures for the entire mineral assemblage

observed in Murchison would be as shown in Table

9. Clearly, a range is represented from very high to

very low temperatures, and statements made in the

literature in the past that C2 meteorites consist of

a high temperature fraction and a low temperature

fraction are somewhat misleading. What is meant,

obviously, is that the most abundant minerals are

the forsterites and the layer-lattice material; all

others are relatively minor in quantity. This frequency distribution might be interpreted as a rapid

drop in temperature from the 1000°C range to the

150°C range, but is more likely a function of bulk

composition of the nebular gas and its state of oxidation with falling temperature. Clearly the cooling

was rapid enough that early formed higher temperature phases did not adjust their solid solution compositions continuously with falling temperature; a

small percentage developed zoned overgrowths instead. The puzzling feature of the sequence of

minerals in Murchison is the complete absence of

feldspar phases, which should appear (under the

perfect equilibrium situation) in the 1100°C-700°C

interval. Their absence may be due to the same

kinetic factor that kept olivine and pyroxene from

adjusting compositions at lower temperatures. Most

of the original Ca and Al are tied up in

the early glasses and spinel. The metastable persistence of these with falling temperatures would

not allow the gas to resorb enough of these elements

to establish the correct composition for condensation of feldspars.

In summary, we consider that early-formed glass

and metal condensed directly by a process like that

described by Blander and Katz (1967), at pressures

of approximately 10"3 atm and temperatures around

1200°C. Hibonite, perovskite, spinel, additional

metal, forsterite, and enstatite formed by approximatedly equilibrium condensation shortly after,

from 1200°C down, so as to poikilitically include

the glass blebs and most of the metal within mainly

forsterite crystals. All lower temperature phases

formed by condensation that may or may not have

been in strict equilibrium with the cooling gas, but

might have involved subcooling, there is no way

to tell. The most puzzling mineralogical aspects

are the very low temperature phases. The spinach

layer-lattice silicate and the poorly characterized

Fe-S-O phase, together exhibit unusual textural

relations with the high temperature phases, including low temperature partial replacement of them.

Restrictions on the thermal history of Murchison

after final consolidation can be deduced from the

stepwise heating experiments of the matrix material as reported in "X-ray Evidence." The maximum temperature at which no changes were

detectable is 245°C. This compares favorably with

thermometers proposed by others for different C2s.

Mueller (1953) found this temperature to be 100°-

350°C for Cold Bokkeveld based on the thermal

decomposition of organic extracts. DuFresne and

Anders (1961) give temperatures between 200° and

300°C for Mighei based on still other considera-
36 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

tions. Thus, reasonable agreement has been

obtained for three C2s from different lines of

evidence.

C2 meteorites represent very early, and very primitive, accreted matter. They may be less primitive

than Cl meteorites. No sequence in time, C1-C2-

C3, however, can be implied since Murchison contains well constituted xenolithic fragments of C3

meteorites. Clearly the formation of at least one

C3 object preceded the formation of at least one

C2 object in the time sense. This suggests that, although a time sequence between the carbonaceous

chondrites does not apply, a spatial sequence must

be the important factor. This would, in turn, indicate spatial fractionation and inhomogeneity with

respect at least to volatiles (C, H, O, N) in the cooling solar nebula.

Note: As this manuscript was being typed, a

paper, "Calcium Variations in Olivines of the

Murchison and Vigarano Meteorites," by R. Hutchison and R. F. Symes, appeared in Meteoritics, 7:

23-29 (1972). Their results for the Ca contents in

Murchison olivines are in accord with those reported here.

Appendix: Description of Wet Chemical Analytical Procedure

A 24-gram piece of the meteorite, free of crust,

was ground in an agate mortar to pass 50 mesh.

Portions of this material were taken for the several

determinations.

H2O- and SiO2

These oxides were determined on one gram samples. The weight loss at 105°C was measured, after

which the material was ignited, fused with sodium

carbonate and silica determined by double dehydration with HC1, ignition to SiO2 and volatization with HF. Silica in the combined filtrates was

determined colorimetrically.

Total Fe, Ti, Mg, Al, Ni, Ca, Na, K, Cr,

Mn, Co, and Cu Determinations

These elements were determined on aliquots of

a solution of 6 grams of the ground sample. The

sample was dissolved in a HF-HC1-HNO3-HC1O4

acid mixture and evaporated to dryness. Repeated

additions of perchloric acid and evaporation to

near dryness with the final addition of a small

amount of hydrochloric acid yielded a water-soluble residue that was diluted to volume. Aliquots of

this "master solution" were used for the various

determinations.

Total Fe, including Ti, was determined gravimetrically by preliminary precipitation with excess

ammonia followed by precipitation of a HC1

solution of the ammonia precipitate with cupferron.

This precipitate was ignited to constant weight at

1100°C and weighed as Fe2O3+TiO2. It was then

dissolved in HC1, iron was separated from titanium

by electrodeposition into a mercury cathode, and

Ti was determined colometrically with peroxide.

Al, Mg, and Ca were determined on a second

aliquot of the master solution. Aluminum was separated from iron by electrodeposition of the iron

into a mercury cathode. It was separated from calcium and magnesium by a double ammonium hydroxide precipitation at pH 7. The hydroxide

was dissolved in acid, evaporated to dryness,

and heated to volatilize ammonium salts. Aluminum was then determined by the method of

Watts (1958). Manganese was removed by the procedure of Peck (1964) prior to the calcium determination. Calcium was separated from magnesium by precipitation as calcium oxalate. The

oxalate was ignited to the oxide, and this residue

was dissolved and then titrated at pH 12.5 with

0.01 molar EDTA, using Acid Alizarin Black SN

indicator (Belcher et al., 1958). Magnesium was

determined by titration with 0.1 molar EDTA at

pH 10 using Calmagite indicator in the filtrate

from the calcium separation.

Cr, Mn, Cu, Co, and Ni were determined colormetrically on separate aliquots of the master solution. Chromium was oxidized to chromate and

reacted with diphenylcarbazide. Manganese was

oxidized to permanganate using periodate. Copper

was reacted with Neo-cuproine (2,9 dimethyl-1,10

phenanthroline). Cobalt was reacted with Nitroso

R salt and nickel with dimethylglyoxime after oxidation with bromine.

Na and K were determined in the master solution by atomic absorption spectroscopy (AAS).
NUMBER 10 37

Total Sulfur, Soluble Sulfur (SO3), and

Elemental Sulfur

Each of these was determined in a separate portion of the sample. For total sulfur approximately

1 gram of sample was sealed in a modified Carius

tube with approximately 10 ml HC1 and 0.5 ml

HC1O4 and heated at 300°C overnight to disintegrate the sample and oxidize all sulfur to sulfate.

The disintegrated sample was transferred to a

Teflon beaker, HNO3, HF, and HC1 added, and

the mixture evaporated to dryness to volatilize

silica. After removal of iron by electrodeposition

into a mercury cathode and a separation of aluminum by double precipitation at pH 7 with NH4OH,

sulfur was determined by precipitation as barium

sulfate.

To determine soluble sulfur a 1 gm sample was

leached for about 20 minutes with 150 ml of boiling

water and then filtered and washed with about 100

ml of water. The filtrate was diluted to volume and

sulfur determined gravimetrically as barium sulfate in a large fraction of the diluted filtrate. The

remaining solution was shown by spectrographic

analysis to contain Ca, Mg, Na, K, and Al. These

elements (except K) were estimated more accurately

by AAS and shown to be present in the molar ratios

(with Na normalized to unity), 7.0 Mg: 2.2 Ca: 1.0

Na: 0.2 Al: 0.1 K*. These cations were equivalent

to 87 percent of the sulfate found.

Elemental sulfur was extracted from the meteorite in a small Soxhlet-like extractor. After evaporation of the solvent the sulfur was oxidized to

sulfate and determined gravimetrically as BaSO4.

About one gram of the material was extracted

for about 1.5 hours with 100 ml carbon tetrachloride. The solvent was then evaporated to dryness,

oxidized with bromine, and sulfur determined. A

blank was run on the carbon tetrachloride. The

sample was then dried at 100°C and reextracted

* K determined by spectrograph only.

with 100 ml of carbon disulfide and sulfur determined in the residue after evaporation of the

carbon disulfide. Most of the extracted sulfur

found, 0.46%, was in the carbon tetrachloride extract while 0.025% was found in the carbon disulfide extract.

Phosphorous Determined Colorimetrically as

Molybdi-vanadophosphoric Acid

About 0.2 grams of the powdered material in a

Teflon beaker was dissolved in a HNO3-HF-HC1O4

mixture and taken to dryness. The residue, free of

silica, was taken up in 6 M hydrochloric acid in

0.001 M sodium bromate, diluted to volume, and an

appropriately sized aliquot passed through a small

anion exchange column to adsorb iron. After rinsing sample from the column the eluate was evaporated to dryness, taken up in water, and phosphorous determined colorimetrically.

C, H, Total H2O, and N

These were determined using a Perkin-Elmer

carbon, hydrogen, nitrogen analyzer, Model 240.

Relatively small samples, 10-15 mg., were taken

for analyses. Ignition at 900°C was employed. An

independent carbon determination was made on a

125 mg sample by ignition at 1100°C in oxygen and

manometric measurement of the evolved carbon

dioxide. This latter determination yielded a carbon

content (1.91%) slightly higher than the value

(1.85%) found using the analyzer at 900°C.

Estimation of Metallic Iron

About 0.75 gram of the sample was extracted

with 3 grams of mercuric chloride in 150 ml of

boiling water in a flask stoppered with a Bunsen

valve for about 2 hours while magnetically stirred.

The solution was then filtered through glass and

iron determined colorimetrically in the filtrate.

Literature Cited

Ahrens, L. H.

1970. The Composition of Stony Meteorites (IX) Abundance Trends of the Refractory Elements in Chondrites, Basaltic Achondrites and Apollo 11 Fines.

Earth and Planetary Science Letters, 10:1-6.

Anders, E.

1971. Meteorites and the Early Solar System. Annual Review of Astronomy and Astrophysics, 9:1-34.

Bass, M. N.

1971. Montmorillonite and Serpentine in Orgueil Me-
SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

teoritc. Geochimica el Cosmochimica Ada, 35:

139-148.

Relcher, R., R. A. Close, and T. S. West

1958. The Complexometric Titration of Calcium in the

Presence of Magnesium: A Critical Study. Talanta,

1:238.

Blander, M., and J. L. Katz

1967. Condensation of Primordial Dust. Geochimica et

Cosmochimica Ada, 31:1025-1034.

Bostrom, K., and K. Fredriksson

1966. Surface Conditions of the Orgueil Meteorite Parent

Body as Indicated by Mineral Associations. Smithsonian Miscellaneous Collections, 151 (3) : 1-39.

Brindley, G. W.

1951. Crystal Structures of Chamosites. Mineralogical

Magazine 29:502-525.

Bunch, T. E., and K. Keil

1971. Chromite and Ilmenite in Non-chondritic Meteorites. American Mineralogist, 56:146-157.

Bunch, T. E., K. Keil, and E. Olsen

1970. Mineralogy and Petrology of Silicate Inclusions in

Iron Meteorites. Contributions to Mineralogy and

Petrology, 25:297-340.

Bunch, T. E., K. Keil, and K. G. Snetsinger

1967. Chromite Composition in Relation to Chemistry

and Texture of Ordinary Chondrites. Geochimica

et Cosmochimica Ada, 31:1569-1582.

Cameron, A. G. W.

1962. The Formation of the Sun and the Planets. Icarus,

1:13-69.

1966. The Accumulation of Chondritic Material. Earth

and Planetary Science Letters, 1:93-96.

Campbell, F.E., and P. Roeder

1968. The Stability of Olivine and Pyroxene in the NiMg-Si-O System. American Mineralogist, 53:257-

268.

Carroll, D.

1970. Clay Minerals: A Guide to Their X-ray Identification. Geological Society of America Special Paper,

126: 80 pages.

Dodd, R. T.

1969. Metamorphism of the Ordinary Chondrites: A Review. Geochimica et Cosmochimica Ada, 33:161-

203.

DuFresne, E. R., and E. Anders

1961. The Record in the Meteorites, V: A Thermometer

Mineral in the Mighei Carbonaceous Chondrite.

Geochimica et Cosmochimica Ada, 23:200-208.

1962. On the Chemical Evolution of the Carbonaceous

Chondrites. Geochimica et Cosmochimica Ada,

26:1085-1114.

Ehmann, W. D., D. E. Gillum, J. W. Morgan, R. A. Nadkarni, T. Rabagay, P. M. Santoliquido, and D. L.

Showalter

1970. Chemical Analyses of the Murchison and Lost City

Meteorites. Meteoritics, 5:131-136.

Fredriksson, K., and K. Keil

1964. The Iron, Magnesium, Calcium, and Nickel Distribution in the Murray Carbonaceous Chondrite.

Meteoritics, 2:201-217.

Freeman, E. S., and B. Carroll

1958. The Application of Thermoanalytical Techniques

to Reaction Kinetics: The Thermogravimetric

Evaluation of the Kinetics of the Decomposition of

Calcium Oxalate Monohydrate. Journal of Physical

Chemistry, 62:394-397.

Frondel, C.

1962. Ferroan Antigorite (Jenkinsite). American Mineralogist, 47:783-785.

Fuchs, L. H.

1968. X-ray Crystallographic Evidence for the Meteoritic

Occurrence of Nepheline. Earth and Planetary

Science Letters, 5:187-190.

1971. Occurrence of Wollastonite, Rhonite, and Andradite in the Allende Meteorite. American Mineralogist, 56:2053-2068.

Fuchs, L. H., K. J. Jensen, and E. Olsen

1970. Mineralogy and Composition of the Murchison

Meteorite. Meteoritics, 5:198 [Abstract].

Goldstein, J. I., and A. S. Doan

1972. The Effect of Phosphorus on the Formation of the

Widmanstatten Pattern in Iron Meteorites. Geochimica et Cosmochimica Ada, 36:51-70.

Goles, G. G.

1969. Cosmic Abundances. In Wedepohl, editor, Handbook of Geochemistry, 1:116-133, Berlin: SpringerVerlag.

Grossman, L.

1972. Condensation in the Primitive Solar Nebula. Geochimica et Cosmochimica Ada, 36:597-620.

Hoyle, F.

1960. On the Origin of the Solar Nebula. Quarterly

Journal of the Royal Astronomical Society, 1:28-55.

Jarosewich, E.

1971. Chemical Analysis of the Murchison Meteorite.

Meteoritics, 6:49-52.

Keil, K.

1968. Mineralogical and Chemical Relationships Among

Enstatite Chondrites. Journal of Geophysical Research, 73:6945-6976.

Keil, K., and L. H. Fuchs

1971. Hibonite [Ca2 (Al, Ti) 24O:W] from the Leoville and

Allende Chondritic Meteorites. Earth and Planetary Science Letters, 12:184-190.

Kerridge, J. F.

1969. The Use of Selected-Area Electron Diffraction in

Meteorite Mineralogy. Pages 500-504 in Millman,

editor, Meteorite Research. Dordrecht, Holland:

D. Reidel Publishing Company.

Kurat, G.

1967. Einige Chondren aus dem Meteoriten von MezoMadaras. Geochimica et Cosmochimica Ada, 31:

1843-1857.

Larimer, J. W.

1967. Chemical Fractionations in Meteorites. I: Con-
NUMBER 10 39

densation of the Elements. Geochimica et Cosmochimica A eta, 31:1215-1238.

Lord, H. C.

1965. Molecular Equilibria and Condensation in a Solar

Nebula and Cool Stellar Atmospheres. Icarus,

4:279-288.

Lovering, J. F., R. W. LeMaitre, and B. W. Chappell

1971. Murchison C2 Carbonaceous Chondrite and Its

Inorganic Composition. Nature, 230:18-20.

Mason, B.

1962-1963. The Carbonaceous Chondrites. Space Science

Reviews, 1:621-646.

1971. The Carbonaceous Chondrites-A Selective Review.

Meteoritics, 6:59-70.

Miller, C. C.

1953. Anhydrous Calcium Oxalate as a Weighing Form

for Calcium. The Analyst, 78:186.

Morey, G. W.

1964. Phase Equilibrium Relations of the Common RockForming Oxides Except Water. U. S. Geological

Survey Professional Paper, 440-L:L70.

Mueller, G.

1953. The Properties and Theory of Genesis of the Carbonaceous Complex Within the Cold Bokevelt Meteorite. Geochimica et Cosmochimica Ada, 4:1-10.

1966. Significance of Inclusions in Carbonaceous Meteorites. Nature, 210:151-155.

Mueller, R. F.

1965. System Fe-MgO-SiO2-O2 with Applications to Terrestrial Rocks and Meteorites. Geochimica et Cosmochimica Ada, 29:967-976.

Onuma, N., R. N. Clayton, and T. K. Mayeda

1972. Oxygen Isotope Cosmothermometer. Geochimica

et Cosmochimica Acta, 36:169-188.

Osborn, E. F., R. C. DeVries, K. H. Gee, and H. M. Kraner

1954. Optimum Composition of Blast Furnace Slag as

Deduced from Liquidus Data for the Quaternary

System CaO-MgO-ALO3-SiO,. Transactions of the

American Institute of Mining and Metallurgical

Engineers, 200:33-45.

Peck, L. C.

1964. Systematic Analysis of Silicates. U. S. Geological

Survey Bulletin, 1170:66.

Pollack, S. S., and W. D Ruble

1964 X-ray Identification of Ordered and Disordered

Ortho-Enstatite. American Mineralogist, 49:983-

992.

Prince, A. T.

1954. Liquidus Relationships on 10 Percent MgO Plane

of the System Lime-Magnesia-Alumina-Silica.

American Ceramic Society Journal, 37:402-408.

Ramdohr, P.

1963. The Opaque Minerals in Stony Meteorites. Journal

of Geophysical Research, 68:2011-2036.

1966. Observations on the Opaque Ore Content of some

Meteorites, Especially from New South Wales.

Journal and Proceedings of the Royal Society of

New South Wales, 99:45-55.

Roedder, E., and P. W. Weiblen

1971. Petrology of Silicate Melt Inclusions, Apollo 11

and Apollo 12 and Terrestrial Equivalents. Geochimica et Cosmochimica Acta, Supplement, 2:

507-528.

Simkin, T., and J. V. Smith

1970. Minor Element Distribution in Olivine. Journal

of Geology, 78:304-325.

Snetsinger, K. G., K. Keil, and T. E. Bunch

1967. Chromite from "Equilibrated" Chondrites. American Mineralogist, 52:1322-1331.

Steadman, R., and P. M. Nuttall

1963. Polymorphism in Cronstedite. Acta Crystallographica, 16:1-8.

Taylor, L. A., G. Kullerud, and W. B. Bryan

1971. Opaque Mineralogy and Textural Features of

Apollo 12 Samples and Comparison with Apollo 11

Rocks. Geochimica et Cosmochimica Acta, Supplement, 2:855-871.

Turekian, K. K., and S. P. Clark

1969. Inhomogeneous Accumulation of the Earth from

the Primitive Solar Nebula. Earth and Planetary

Science Letters, 6:346-348.

Van Schmus, W. R.

1967. Polymict Structure of the Mezo-Madaras Chondrite.

Geochimica et Cosmochimica Acta, 31:2027-2042.

1969. Mineralogy, Petrology, and Classification of Types

3 and 4 Carbonaceous Chondrites. Pages 480 to 491

in Millman, editor, Meteorite Research. Dordrecht,

Holland: D. Reidel Publishing Company.

Watts, H. L.

1958. Volumetric Determination of Aluminum in Presence of Iron, Titanium, Calcium, Silicon and Other

Impurities. Analytical Chemistry, 30:967.

Whipple, F. L.

1966. Chondrules: Suggestion Concerning the Origin.

Science, 153:54-56.

Wood, J. A.

1963. On the Origin of Chondrules and Chondrites.

Icarus, 2:152-180.

1967a. Olivine and Pyroxene Compositions in Type II

Carbonaceous Chondrites. Geochimica et Cosmochimica Acta, 31:2095-2108.

1967b. Chondrites: Their Metallic Minerals, Thermal Histories, and Parent Planets. Icarus, 6:1-49.

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