SMITHSONIAN CONTRIBUTIONS TO THE

EARTH SCIENCES

NUMBER 5

Roy s.ciarke, jr., The Allende, Mexico,

Eugene larosewich, Brian Mason. ^«- , • o i

JosephNelen.ManuelGomez, Meteorite Shower

and Jack R. Hyde

SMITHSONIAN INSTITUTION PRESS

CITY OF WASHINGTON

I97O
ABSTRACT

Clarke, Roy S., Jr., Eugene Jarosewich, Brian Mason, Joseph Nelen, Manuel

G6mez, and Jack R. Hyde. The Allende, Mexico, Meteorite Shower. Smithsonian

Contributions to the Earth Sciences 5:1-53. 1970.—The Allende meteorite fell near

Parral, Chihuahua, Mexico, between 0105 and 0110 Central Standard Time on

Saturday, 8 February 1969. The fireball approached from the south-southwest

(S37°W), and broke up in the atmosphere, producing thousands of fusion-crusted

meteoritic stones. The smallest individuals were recovered 4 km east of Rancho

Polanco (26°43'N, 105°28/W), and the largest near Rancho El Cairo (27°06/N,

105°12/W), some 50 km to the north-northeast across the Parral-Jimin^z highway.

Specimen size increases generally as one moves to the north-northeast within the

field, and many large specimens (5-15 kg) were recovered in and around the area

enclosed by Pueblito de Allende, San Juan, Rancho Blanco, and Santa Ana. At

least two tons of meteoritic stones have been recovered, with crusted individuals

ranging in weight from approximately 1 g to one individual of 110 kg. Specimen

shapes are mainly fragmental, due to one major disruption of the parent body,

followed by minor subsequent fragmentation. Individual stones have primary and

secondary fusion crust, and some fresh fracture surfaces due to late-stage breaking.

A small percentage of stones shows strong ablative shaping due to oriented flight.

The elongate strewnfield possibly exceeds 300 km2 in area, making Allende the

largest recorded stony meteorite fall both in its areal extent and in total weight

of recovered meteorites. Allende fell near the sites of find of two major iron

meteorites, Morito and Chupaderos.

Chemical and mineralogical compositions establish that Allende is a Type III

carbonaceous chondrite. Three distinct components can be recognized: finegrained black matrix (~60%), chondrules (~30%), and irregular white aggregates (^10%). The matrix consists almost entirely of iron-rich olivine

(average 50% Fe2SiO4), with minor amounts of troilite, pentlandite, and taenite,

rendered opaque by dispersed carbonaceous material. Most of the chondrules are

magnesium-rich, and consist of olivine (average 9% Fe2SiO4) with minor amounts

of clinoenstatite and some glass; a few chondrules are rich in calcium and aluminum, and are made up largely of anorthite, gehlenite, augite, and spinel. The

irregular aggregates are also rich in calcium and aluminum, and contain anorthite,

gehlenite, augite, spinel, nepheline, grossular, and sodalite (the last two minerals

have not previously been recorded from meteorites). Complete chemical analyses

have been made of the bulk meteorite, a dark inclusion, the matrix, a chondrule

concentrate, two individual chondrules, and a single aggregate.

Official publication date is handstamped in a limited number of initial copies and is recorded

in the Institution's annual report, Smithsonian Year.

UNITED STATES GOVERNMENT PRINTING OFFICE

WASHINGTON : 1970

For sale by the Superintendent of Documents, U.S. Government Printing Office

Washington, D. C. 20402 - Price $1.25
Contents .

Page

Abstract • • "

Acknowledgments 1

Introduction -. 1

Specimen recovery and distribution for study 2

Published reports • 2

Proposed name : 2

Strewnfield '. • 2

' Distribution of specimens 6

Recovery of individual stones 9

Other meteorites from the Parral-Jim£nez area. 15

Morphology ... ; 1?

Mineralogy and petrography 32

Fusion crust ' 42

Chemical composition 44

Comparative chemical data 47

Discussion 47

Literature cited 52

Tables

Page

1. Minerals in the Allende meteorite 33

2. Microprobe analysis of gehlenite, fassaite, and anorthite in a large chondrule 39

3. Analytical data on the Allende meteorite 45

4. Trace element data on the Allende meteorite 47

5. Comparison of chemical data on the Allende meteorite 50

6. The Type III carbonaceous chondrites 51

Illustrations

Page

1. Location of Allende meteorite strewnfield 3

2. Plan of the Allende meteorite strewnfield 4

3. Field recovery by Brian Mason of a 12-kg Allende specimen (NMNH 3527) near

San Juan 8

4. An Allende individual (NMNH 3491) found in place near Rancho Santa Ana 10

5. An Allende individual found by Manuel G6mez near Rancho Santa Ana

(NMNH 3493) 11

6. An Allende stone found partially embedded at base of cactus plant (NMNH 3494) 12

7. An Allende individual (NMNH 3502) found by local boy near Rancho Blanco 13

8. An Allende individual found near schoolhouse in San Juan (NMNH 3517) 14

9. Location of meteorites of the Parral-Jim6nez area 16

10. A blocky, crusted Allende individual (NMNH 3523) found between Pueblito de

Allende and San Juan 18

11. An Allende individual (NMNH 3500) found near Rancho Blanco 19

12. An Allende individual (NMNH 3501) found near Rancho Blanco 20

13. An Allende stone (NMNH 3494) found at base of cactus near Rancho Santa Ana 20

14. An unusually large, oriented Allende individual (NMNH 3527) found near San Juan.. 21

15. An aerodynamically shaped Allende individual found near Torreon de Mata

(NMNH 3522) 22

iii
iv

Page

16. An aerodynamically shaped Allende stone (NMNH 4018) found near the Ceniceroses.. 23

17. An aerodynamically shaped Allende individual found near Cienega de Ceniceros

de Arriba (NMNH 4083) 24

18. An aerodynamically shaped Allende individual found near Cienega de

Abajo (NMNH 4084) 25

19. An aerodynamically shaped Allende individual found near the Ceniceroses

(NMNH 4157) 26

20. An unusually large Allende stone (NMNH 4006) found near Cienega de

Ceniceros de Abajo 27

21. Lustrous fusion crust on an Allende stone (NMNH 3812) found near the Ceniceroses.. 28

22. Lustrous fusion crust on an Allende stone (NMNH 3813) found near the Ceniceroses.. 29

23. Lustrous fusion crust on an Allende stone (NMNH 3814) found near the Ceniceroses.. 30

24. Broken surfaces of an Allende fragment (NMNH 3529) 31

25. Polished surface of an Allende slice (NMNH 3529) 32

26. Electron micrographs of Allende meteorite matrix 34

27. Composition of individual olivine grains in Allende chondrules 35

28. Irregular aggregates and chondrules in black matrix 36

29. Allende meteorite chondrule of prismatic olivine crystals 37

30. Allende meteorite barred olivine chondrule 37

31. Three juxtaposed barred olivine chondrules 38

32. Allende meteorite granular olivine chondrule 39

33. Gehlenite-anorthite-fassaite-spinel chondrule 40

34. Anorthite-forsterite-spinel chondrule 41

35. A mosaic of photomicrographs of lustrous fusion crust (NMNH 3811) 43

36. SiOa plotted against MgO for chemical analyses of chondrites 48
Roy S.Clarke, Jr.,

Eugene Jarosewich, Brian Mason,

Joseph Nelen, Manuel Gomez,

and Jack R. Hyde

The Allende, Mexico,

Meteorite Shower

Introduction

In the early morning of Saturday, 8 February 1969

(between 0105 and 0110 Central Standard Time), a

brilliant fireball was observed over much of northern Mexico and adjacent areas of Texas and New

Mexico. The most spectacular phenomena were

centered around the city of Hidalgo del Parral in

the south-central part of the state of Chihuahua.

The fireball approached from the south-southwest,

and as it neared its terminal point the brilliant

light was accompanied by tremendous detonations

and a strong air blast. Thousands of individual

meteoritic stones rained down over a large area of

rural Mexico. One weighing 15 kg fell within four

meters of a house in the town of Pueblito de Allende, 35 km east of Parral. This stone was broken

up, and pieces taken to the office of the newspaper

"El Correo de Parral" the same day; the news of an

important meteorite fall was published that evening. Dr. E. A. King of the NASA Manned Spacecraft Center in Houston, Texas, heard of these

events on the morning of 10 February 1969 and departed promptly for the scene. He returned with

meteoritic material on the morning of 12 February,

and he and his colleagues have published a preliminary report on their findings (King et al., 1969).

Our initial field investigation was undertaken

after conferring by telephone with Ing. Diego

Cordoba, Director del Instituto de Geologia, Mexico

City. Roy S. Clarke and Brian Mason arrived in

Parral on Wednesday, 12 February and spent the

next five days investigating the fall and collecting

Roy S. Clarke, Jr., Eugene Jarosewich, Brian Mason, and

Joseph Nelen, Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20560. Manuel Gdmez, ASARCO Mexicana SA.,

Parral, Chihuahua, Mexico, and Jack R. Hyde, Smithsonian

Institution Meteorite Recovery Project, Lincoln, Nebraska

68508.

material for research and preservation. Ing. Manuel

G6mez of ASARCO Mexicana S. A., Parral, and Ing.

Ce'sar Gallardo of the University of Chihuahua

joined the field party and contributed importantly

to its success. Clarke returned to the field 24-27 May

with Jack R. Hyde of the Smithsonian Institution's

Meteorite Recovery Project, Lincoln, Nebraska.

Hyde remained in the area for several weeks conAcknowledgments

We are indebted to Ing. Diego Cordoba, Director del Instituto de Geologia, Mexico City,

for permission to investigate the fall area and

to collect material for scientific investigation;

to R. C. Byrd, Superintendent, ASARCO Mexicana, Parral, for providing facilities for our

work; to R. E. McCrosky and Gunther Schwartz of the Smithsonian Institution Astrophysical Observatory for field assistance and

informative discussion and interpretation of

phenomena of fall observations. Our co-workers within the Department of Mineral Sciences,

National Museum of Natural History, have

contributed to this work in various ways: John

S. White, Jr. prepared many X-ray powder

photographs; E. P. Henderson prepared photomicrographs and provided helpful discussion;

Grover C. Moreland prepared critical sections

for study; Sarah W. Scott cataloged field collections and assisted in preparation of the manuscript; and William G. Melson critically reviewed the manuscript and provided helpful

discussion. We are indebted to the National

Aeronautics and Space Administration for

grants that covered part of the costs of this

investigation.
SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

ducting studies of specimen distribution, and he

returned to the field for an additional three weeks

in late October and November.

SPECIMEN RECOVERY AND DISTRIBUTION FOR STUDY.—

Information related to the fall and recovery of the

Allende meteorite was disseminated rapidly to interested scientists throughout the world by the

Smithsonian Institution's Center for Short-Lived

Phenomena, Cambridge, Massachusetts. Specimen

material reached the Division of Meteorites, National Museum of Natural History, Washington, on

19 February, and its distribution to interested scientists began immediately. All reasonable requests

were granted; scientists in thirty-seven laboratories

in thirteen countries were sent material within a

few weeks of the date of fall. Dr. E. A. King's group

in Houston had also distributed material to other

research laboratories.

Many individual meteorite specimens have been

recovered from the strewnfield, and Allende material is now widely distributed in collections and

research laboratories. We obtained about 150 kg of

meteorites on our first trip into the field and smaller

amounts on the second and third trips, and we were

shown many large specimens that we were unable

to acquire. Several other scientific groups from institutions in Mexico and the United States are

known to have visited the area and acquired material, as has one Canadian group. Commercial and

private collectors have been active in the area and

have removed indeterminate amounts of specimen

material. One dealer reported handling approximately 500 kg of Allende meteorites on a wholesale

basis by early November 1969. An aggressive amateur collector visited the field in late February and

obtained 110 kg of excellent material for his collection. Information of this type leads us to conclude

that during the first five months after the fall two

tons of meteorite specimens were removed from the

strewnfield. The recovery of this large quantity of

specimen material establishes the Allende meteorite

as the largest stony meteorite shower on record.

PUBLISHED REPORTS.—The immediate and broad

distribution of Allende meteorite specimens has resulted in the prompt publication of several studies

that are not referred to directly in this paper. Fireman (1969) published a preliminary account on the

field recovery and laboratory study of Allende. A

report on the atmospheric collection of meteoritic

debris associated with the Allende fireball has been

prepared by Carr (1970). The study of a number

of radionuclides in Allende by gamma-ray spectrometry has been reported by Rancitelli et al. (1969).

Fireman et al. (1970) have reported several types of

ages for Allende based on determination of rare

gases^ K, U and Th, and Durrani and Christodoulides (1969) have used thermoluminescence as a

means of estimating an exposure age for Allende.

PROPOSED NAME.—We propose the name "Allende"

for this meteorite, although "Pueblito de Allende"

was used in the preliminary report of King et al.

(1969), because this town was the location of the

first stone known to have been recovered. The extent of the strewnfield was not fully realized at that

early date, and it is now clear that the name Allende

has an association with a large area in the heart of

the strewnfield. Specimens have been recovered

within a kilometer of the historic and beautiful

town of Valle de Allende, from along a 15-km segment of the valley of the Rio del Valle de Allende,

as well as in the environs of Pueblito de Allende.

Hey (1966) comments in the introduction to his

standard Catalogue of Meteorites that "meteorite

names are essentially labels, of no intrinsic significance." Labels should be simple and concise, and

the name Allende satisfies these criteria admirably.

The name honors Ignacio Jose* Allende (1779-1811),

a Mexican army officer and patriot of the uprising of

1810-1811.

Strewnfield

The Allende fireball approached from the southsouthwest, the azimuth of the radiant (direction of

approach) being approximately 215° and its altitude 13° (preliminary values, McCrosky et al.,

1969). The resulting meteorite strewnfield is located

540 km (340 statute miles) south (S10°E) of El

Paso, Texas, and 200 km south (S20°E) of the city

of Chihuahua, to the east of the Sierra Madre Occidental (Figure 1). Its head lies within and somewhat to the east of a small group of hills, the Sierra

de Almoloya, just north of the Interamerican Highway (Route 45), halfway between the cities of

Parral and Jimenez. Small individual meteorite

specimens from the tail of the field have been recovered as far south as 4 km east of Rancho Polanco,

26°43'N and 105°28/W (Figure 2). Approximately

50 km to the north-northeast a large individual
NUMBER 5

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SAN ANTONIO

TORREON

ALLENDE MEXICO METEORITE STREWNFIELD

» . DIRECTION of FIREBALL

KILOMETERS

FIGURE 1.—Location of the Allende meteorite strewnfield, with direction of fireball approach indicated.

stone of approximately 110 kg, broken into many

fragments on impact, was discovered at 27°O6'N and

105°12'W, just to the east of the Sierra de Almoloya.

The specimen-rich Allende meteorite recovery

area, 50 km in length and possibly exceeding 300

km2 in area, is the largest stony meteorite strewnfield that has been studied in any detail.1

 The map

1

 The recent fall of the Belfast (Bovedy), Northern Ireland,

meteorite resulted in the recovery of two stones separated by

a distance of 62 km (Meighan and Doughty, 1969), and the

suggestion that the main mass continued on for 150 km into

the Atlantic Ocean (Hindley and Miles, 1970). Kulik (1922)

reported that stones from the Saratov, Russia, meteorite fall

were found over a distance of 130 km, but details are lacking.

Nininger (1936) reported that specimens of the Pasamonte,

New Mexico, meteorite shower were separated by a distance

of 28 miles (45 km).

presented here (Figure 2)

 2 is based largely on our

own field investigations and may not indicate the

full extent of the field. We feel, however, that the

general shape of the field and the nature of the

distribution of samples within it are fairly well

understood at this time. Large individual specimens

may still be found, extending the field to the northeast and perhaps modifying the shape of that end

2

 The maps presented here (Figures 2 and 9) are based on

1:250,000 sheets compiled in 1964. They were prepared as a

collaborative effort of the Departmento Cartografico Militar

de Mexico, the Inter-American Geodetic Survey, and the Army

Map Service of the United States, based on aerial photographs

taken in 1957-1958. They are available from the Mexican

Government. The two sheets used were:

Hidalgo del Parral, Chihuahua. NG13-5, series F501.

Ciudad Camargo, Chihuahua. NG13-2, series F501.
105-30' 105° 15'

ALLENDE METEORITE STREWNFIELD

CHIHUAHUA, MEXICO

0 1 2 3 4 5

A METEORITE SPECIMEN

SCALE Kilometers

• RANCHO SAN AGUSTIN

HACIENDA OJODE LA SIERRA DEALMOLOYA /

ESTACION TROYA

RANCHO SAN ISIDRO

/RANCHO EL CAIRO

PORVENIR

RANCHO. LAS CAMELIAS

E JIDO LA PORRENA

• SAN JUAN /

/

 l2llfl

 .RANCHO BLANCO

UEBLITO DE ALLENDE

V

SANTA ANA

RANCHO SANTA ISABEL

pRANCHO SAN ANTONIO

ALLE DE ALLENDE

EJ.DOLA PALMA. ^.^NCH O f 8 DEUCIA 8

LA MAGDALENA.V\. "RANCH O SAN JOSE

CIENEGA DE CENICEROS DE ARRIBA. . ,

^ ^ Jf .v/'-^»CIENEGA DE CENICEROS DE ABA JO

•RANCHO LOS OJUELOS

wEJIDO VALSEQUILLO

N37°E N35°E N32°E

IO5°3O'

FIGURE 2.—Plan of the Allende meteorite strewnfield.

of the field somewhat. We do not expect subsequent

work to require major changes in the shape of the

field south of the Rio del Valle de Allende.

The map (Figure 2) shows the outline of the

strewnfield and its relation to major geographic

features and habitations. The strewnfield boundaries were arrived at largely on the basis of interviews with many local residents who had searched
NUMBER 5

for specimens or who had knowledge of where they

were recovered. Specimen collecting by the local

people started immediately after the fall and continued with more or less enthusiasm for months.

The intensity of this activity depended somewhat on

the interest stimulated at a given period by outsiders and by the varying labor requirements of an

agrarian economy. Meteorite collecting proved to

be an interesting and profitable leisure-time activity

for a few individuals in each community, and these

collectors were a particularly reliable source of information needed to reconstruct the specimen distribution pattern. All of the habitations indicated

on the map (Figure 2) were visited; the important

ones on many occasions, and most at least several

times over a period of weeks or months.

There is an unavoidable vagueness in much of the

information obtained from local residents. Individuals were mainly open and frank in their reports

to us, but their meteorite finds had not been documented with scientific precision. Specimens were

collected over a period and kept together at home in

a box, bag, or sack. Plastic bags which had previously been used for candy or meal and had not been

well cleaned were a favorite storage method for collections of small specimens. Normally, a given individual collected from a relatively small area within the strewnfield. Collectors generally had sharp

recollections of the location where unusual specimens or particularly large ones were found, but it

was impossible to revisit each site. Distances and

directions are also subject to question, our practice

being to record reports as we received them. Landmarks are scarce in the chaparral country, possibly

introducing another uncertainty. Occasionally,

claftns were made that seemed to be at variance with

the developing pattern, and these reports were rejected unless corroborative evidence could be found.

Generally speaking, we would receive numerous reports of meteorites being found in a given area, and

equally numerous reports of their absence from

other areas. In particularly critical areas, we conducted limited searches, normally with the assistance

of local residents.

The degree of confidence we have in the boundaries developed is indicated on the map (Figure 2)

by use of either a solid or broken line. The area of

most uncertainty is north of the highway, where the

two largest specimens have been found. Does the

strewnfield really extend further to the northeast,

perhaps even beyond the railroad? The area south of

the highway between Rancho Las Camelias and the

town of Salaices seems also to be in question, specimens so far not having been reported from there.

An axis of the strewnfield based on specimen recovery was drawn by joining the point where small

specimens were found in the extreme southwest

with the locations of the largest specimen (Figure

2). This line, N32°E, is in good agreement with the

azimuth of 215° (N35°E) calculated by McCrosky

et al. (1969) from fireball observations. The N35°E

line is also indicated on the map, assuming the location of the largest specimen to be most representative of the fireball trajectory. It is interesting to note

that the three specimens found north of the highway, separated by a maximum distance of 7 km, plot

closely to both of these lines. The shape of the

strewnfield and the distribution of specimens within

it (discussed below) suggest that the N35°E line approximates the axis of the strewnfield corrected for

preferential scattering of lighter specimens due to

high-altitude winds. McCrosky et al. (1969) reported that data for the time of fall supplied by the

United States Air Force indicated winds "predominantly from the west up to an altitude of 30 km

except for the immediate surface layer where northeast winds may have been occurring." These west

winds would be consistent with an eastward skewing

of the tail of the strewnfield, a situation that seems

to be borne out by the observed distribution of

specimens.

The outline of the strewnfield might be somewhat easier to understand if one assumed that the

actual trajectory of the fireball was from a slightly

more westerly direction than the N35°E bearing of

McCrosky et al. (1969) . Justification for such an

assumption can be derived from considerations of

three key specimens from accurately known locations within the strewnfield. The 110 kg specimen

from the head of the field has been mentioned above

and its location is indicated in Figure 2. A 40-50

kg individual was found within the Sierra de Almoloya 5 km to the southwest of the largest specimen (Figure 2, and discussed below). The third

specimen was found 12 km to the southwest of the

110 kg individual (NMNH 3527, discussed below),

near San Juan (Figure 2). This specimen is a 12 kg

aerodynamically oriented individual, and it seems

reasonable to assume that a specimen of this type

would fall with relatively little deflection during
SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

passage through the atmosphere, falling close to

the fireball's actual trajectory. Similar assumptions

for the other two specimens based on their size also

seem reasonable. These three specimens lie on a

straight line with a bearing of N37°E, a bearing that

fits well the configuration of the strewnfield. The

asymmetry of the field along this line can be reasonably explained as due to high-altitude winds. The

light material that fell in the tail of the field may

have been moved to the east by 4 km or more, while

the eastern border of the main body of the field

may have been skewed eastward by approximately

2 km. This picture seems reasonable to us on the

basis of our field observations and study of specimen

distribution (discussed below).

The character and use of the land within the

strewnfield is largely controlled by elevation and

drainage patterns. The area is traversed by the

drainage systems of the Rio del Valle de Allende

in the north and the Rio Primero in the south. The

Rio Primero is an intermittent stream, dry for most

of the year. Habitation is concentrated along these

streams at the borders of areas of intense agricultural use. Agriculture and habitation account for

10-15 percent of the land use within the strewnfield,

and there is some mining in the area. With only a

slight rise in elevation away from these streams,

the land changes to brush-covered range country

known as chaparral. Much of the chaparral is relatively open, but it does include areas of dense brush,

penetrable only with difficulty. To the southwest

from the Rio del Valle de Allende, the country

generally becomes more open and drier.

Changes of elevation within the strewnfield are

generally gradual with the marked exception of the

Sierra de Almoloya (2,044 meters maximum elevation) . Elevations tend to increase to the southwest and range from 1,500 to 1,750 meters. The Rio

del Valle de Allende meanders across the upper

part of the field for a distance of almost 20 km, elevations along the river ranging from 1,550 meters

east of San Juan and Rancho Blanco to near 1,600

meters just east of Valle de Allende. The elevation

of the Rio Primero where it crosses the tail of the

field near the twin villages of Ceniceros is 1,650

meters. From here elevations increase gradually to

the southwest, reaching 1,750 meters just east of

Rancho Polanco.

DISTRIBUTION OF SPECIMENS.—The weight distribution of individual, crusted Allende meteorite specimens within the strewnfield approximates the pattern that would be expected, assuming one major

disruption of the parent meteorite followed by limited further breakup of smaller fragments during

high-velocity flight. Atmospheric drag combined

with the low angle of entry produced unusually effective size sorting over a long strewnfield. This is

clearly demonstrated by the observed distribution of

specimens on the ground and is further supported

by morphological observations that will be discussed

in a following section. Several of the largest individual pieces were apparently relatively undeflected

in their flight through the atmosphere and traveled

the greatest distance to the northeast after initial

breakup, well beyond the bulk of specimens. Largeto medium-size fragments traveled less far and were

apparently deflected by the atmosphere to an extent

depending largely upon their individual shapes.

This resulted in a broadening of the strewnfield in

the area that produced most of the large specimens.

Smaller specimens were retarded more promptly by

atmospheric drag—falling many kilometers behind

the largest individuals—and were not deflected far

from the fireball's trajectory. This summary is, of

course, an oversimplification, but it furnishes a

useful framework for discussion of our field observations.

The largest specimen known to us is a 100-110 kg

fragmented individual which was discovered eight

months after the fall. It was found approximately

1.5 km N15°E of Rancho El Cairo (Figure 2), in

and around a small hole. The second largest stone

was found in early April in the Sierra de Almoloya

4 km north of Route 45 at a point north of Rancho

Las Camelias. This was a 40-50-kg individual that

also fragmented on impact. We know of only one

other stone recovered north of the highway, a 6-kg

individual. Two large stones were recovered south

of the highway and within a few hundred meters of

it, a 35-kg individual recovered northeast of San

Juan (NMNH 3529, broken on impact) and a 17-kg

individual recovered directly north of San Juan

(NMNH 3509, broken on impact). A number of

specimens in the 5-20-kg size range have been recovered around San Juan and Rancho Blanco and

in the area extending southeast from Rancho Blanco

for several kilometers. A somewhat isolated 18 kg

individual was recovered in range country 7 km

south of Rancho Blanco (Donald P. Elston, personal communication, 1969), and several other large
NUMBER 5

individuals (5 to 11 kg) have been recovered 2 to 3

km to the north and northwest of this 18 kg individual. Many other large individuals have been

found in the agricultural area enclosed by the four

locations Pueblito de Allende, San Juan, Rancho

Blanco, and Santa Ana. The largest individual

that we know of that landed without damage was

recovered at the edge of the river between Pueblito

de Allende and Santa Ana (NMNH 3528, 18.5 kg).

A 12-kg individual (Figures 3 and 14) was recovered

in a freshly plowed field less than one kilometer

south of San Juan (NMNH 3527, found by B.

Mason on 17 February 1969) . Small specimens have

been found interspersed among the large specimens

at the north end of the field, but in very limited

numbers. An example is a 26 g completely crusted

individual that was found within 2 to 3 km of

Rancho Blanco (NMNH 4651). The range country

south from Rancho Blanco and Santa Ana and extending west toward Rancho San Antonio produced

many medium-size specimens (1 to 5 kg) and occasional larger ones. Specimens in this size range

were also found as far south as several kilometers

southeast from Valle de Allende, and 1-kg specimens have been found as far south as "Rancho

(ruinas)."

South from Rancho (ruinas) and 10 km south

of Valle de Allende is the comparatively isolated

village of Torre6n de Mata (population, approximately 50). This village has served as an important

collecting point for the south-central region of the

strewnfield. Specimens were recovered here immediately after the fall, but the local people do not appear to have been greatly impressed by the abundance of valuable meteorite material close at hand.

Specimens were found within the village and on

the farmland nearby, and in the range country to

both the north and south. Some of the more enthusiastic residents of villages to the north walked

or rode horseback from the vicinities of Pueblito de

Allende and Valle de Allende to Torre6n de Mata

searching for specimens. This activity undoubtedly

attracted attention, but the local people seem to

have felt that the small specimens found in their

area were of little value compared to the commercially attractive large specimens found to the

northeast. Five kilometers farther to the southwest

are the twin villages of Cienega de Ceniceros de

Arriba and Cienega de Ceniceros de Abajo (combined population, approximately 500). They served

as collecting centers for hundreds of small specimens recovered from the tail of the strewnfield.

Little collecting was done in this area prior to

the visits of Jack R. Hyde in June 1969. These

visits stimulated searches that led to the recovery

of an important research collection and to extending the strewnfield as far south as several kilometers

east of Rancho Polanco.

The general trend of decreasing specimen size

that was observed for the head and center of the

strewnfield holds for the tail. This is demonstrated

by calculating average specimen size for collections

made (1) around Torre6n de Mata, (2) the Ceniceroses, and (3) in the extreme tail of the field.

Collections made around Torre6n de Mata naturally include material collected toward the Ceniceroses, and the converse is true for collections

obtained in the Ceniceroses. Torre6n de Mata material, however, has a strong bias for areas to the

north and northeast, while material from the Ceniceroses would not normally have been collected as

far north as Torre6n de Mata. The specimens from

the tail of the strewnfield were collected at least

5 km south of the Ceniceroses and on to the end

of the field. The approximately 200 specimens

known to have been collected in the Torre6n de

Mata area range in weight from 6 to 537 g, with an

average weight of 87 g. A somewhat larger collection of specimens known to have been collected

around the Ceniceroses range in weight from 2 to

540 g, with an average weight of 32 g. The small

group of specimens (17) from the tail of the field

ranged in weight from 3.1 g (completely crusted

individual) to 43 g, with an average weight of 12 g.

Individual specimen weight on the average decreases

as one moves to the southwest within the strewnfield.

It is tempting to try and estimate the amount of

Allende meteorite material that reached the ground.

We pointed out above that an estimated two tons

of material was removed from the strewnfield during

the first few months after its fall. What fraction of

the material that actually landed does this represent? An important factor to consider is the effectiveness of search and recovery operations within

the strewnfield. The areas of maximum concentration of large specimens fortuitously and fortunately

coincided with or were contiguous to areas of maxi-
FIGURE 3.—The field recovery by Brian Mason of a 12-kg Allende specimen (NMNH 3527) 17

February 1969, approximately 0.7 km south of San Juan: a, specimen in front of notebook,

nearly buried in recently plowed field; b, close-up of specimen in place, with pocketknife handle

for scale. Two large pieces and several small fragments recovered. See Figure 14.
NUMBER 5

mum population density. These areas have been

searched extensively by the local people, although

little in the way of systematic searching has been

undertaken. Large areas of the strewnfield have been

given only cursory attention, while remote and

impenetrable areas of the field remain essentially

unexamined. An indication of the nature of the

problem is the fact that the 110-kg specimen mentioned above was not discovered until eight months

after the fall, and specimens as large as 5 kg were

still being found in the intensively searched area

around Rancho Blanco (NMNH 4646) and San

Juan (NMNH 4655) in early June, four months

after the fall. A 14-kg specimen was reported to

have been found near Rancho Blanco in midNovember. Probably only 40 to 60 percent of the

meteorite material that hit the ground has been

recovered to date, leading us to suggest that the

minimum amount of material that comprises the

Allende shower was of the order of four tons. The

possibility exists, of course, that this estimate is

too conservative. Field investigation should be continued in the Allende strewnfield as long as significant amounts of meteorite material are recoverable.

RECOVERY OF INDIVIDUAL STONES.—In this section

notes are given on the circumstances of recovery of

specific stones. The stones selected are from those

for which we have particularly reliable information,

and those that are of unusual interest in developing

the distribution pattern within the strewnfield.

The largest specimen that has been recovered to

date was not found until 8 October 1969, eight

months after it fell. Guadalupe Juarez of Rancho

El Cairo was working in a bean field when he noticed a rabbit run into an adjacent uncultivated

area. He got his gun and pursued the rabbit some

150 yards into the chaparral where he discovered

the 110-kg fragmented meteorite. The soil was hard

and consisted of compacted clay containing approximately 70 percent small stones. The meteorite had

produced a spoon-shaped hole with a one- to threeinch raised rim at the north end. It was 13 inches

deep at the north end, the bottom sloping smoothly

to ground level at the south end. The hole was 32

inches wide, 52 inches long, and had an apparent

axis of N21°E, The largest individual piece recovered was about 6 kg, and the larger pieces were

mainly distributed 12 to 15 feet from the hole,

around its north end. At least 20 kg of dust and

pieces in the 1- to 3-g size range were recovered,

mainly from within the hole.

Comments on individual specimens are given

below:

NMNH 3491, 1.8 kg, approximately 3 km south to

southeast of Rancho Santa Ana.

A completely crusted individual found in place by

schoolboys in our party just prior to a brief but

heavy rainstorm about noon on 13 February 1969

(Figure 4). It was embedded in hard ground, penetrating perhaps 5 cm at maximum. Figure 4c is a

photograph of this specimen oriented similarly to

the position shown in the ground. Thin fusioncrust development on the flat surface to the upper

right in both photographs establishes that this was

a posterior surface during high-velocity atmospheric

flight. This specimen seems to have hit the ground

at a high angle, falling close to the trace of the

fireball's trajectory (Figure 2) . A small amount of

dirt adhered to the specimen as it was removed

from the hole. It is one of many specimens found in

contact with dry grass that showed no signs of

charring.

NMNH 3492, 22 g, approximately 3 km south-southeast of Rancho Santa Ana, within a few hundred

meters of NMNH 3491.

This specimen is a small fragment free of any obvious fusion crust. A cursory search of the immediate surroundings produced no additional material.

It was found by a member of our party on the

morning of 13 February 1969.

NMNH 3493, 7.5 kg, approximately 3 km south of

Rancho Santa Ana.

This specimen was found by Manuel G6mez while

running for shelter during the rainstorm about

noon on 13 February 1969. It is a large, flatironshaped individual that landed on hard ground,

making a shallow abrasion (Figure 5). The specimen broke into two large pieces (4.8 and 2.5 kg),

a small piece (115 g), and several small fragments.

The largest piece was found about 1.5 m from

the impact point and the other large piece was

an additional meter away. Some of the smallest

fragments were found yet farther away and are

being pointed out in the photograph (Figure 5b).

The alignment of the pieces with the point of im-
10 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

FIGURE 4.—A 1.8-kg Allende individual (NMNH 3491) found in place approximately 3 km south to southeast of Rancho

Santa Ana, 13 February 1969; a, in place, pocketknife for scale; b, rolled out of hole; c, enlarged view oriented as in a.

Scale bar in c, 2 cm.
NUMBER 5 11

FIGURE 5.—A 7.5-kg Allende individual found by Manuel G6mez on 13 February 1969 approximately 3 km south of Rancho Santa Ana (NMNH 3493). Specimen hit abraded area to right of

boy's foot, a, Largest piece marked by sunglasses, a second large piece farther away and in line

with impact point. Small fragments are being pointed to in b.
12

SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

FIGURE 6.—A 7.0-kg Allende individual found partially embedded at base of cactus plant on 13

February 1969 (NMNH 3494). Sunglasses for scale. Found 3 to 4 km south of Rancho Santa Ana.

See Figure 13.

pact was in the direction N40°E, in good agreement with the suggested strewnfield axis.

NMNH 3494, 7.0 kg, 3 to 4 km south of Rancho

Santa Ana.

This specimen was found by a Mexican helper during the rainstorm on the morning of 13 February

1969 embedded at the base of a cactus plant. It is

possible that the upper part of the plant was damaged by the essentially vertical descent of the specimen, but the damage may also have been caused by

cattle (Figure 6). The specimen was buried approximately one-third its depth in the relatively

soft earth at the base of the cactus.

NMNH 3495, 4.0 kg, approximately 2 km southeast

of Rancho Santa Ana.

This specimen was sighted in a plowed field by a

Mexican helper from a truck moving slowly along

an adjacent road. The specimen was about 25 m

from the road and had buried itself to about half

its depth. It was found in the early afternoon of

13 February 1969.

NMNH 3502, 2.0 kg, approximately 200 m west of

Rancho Blanco.

This completely crusted individual was found undisturbed on the afternoon of 14 February 1969

by a boy in our field party. It landed on hard,

pebbly ground in a chaparral area and made virtually no impression (Figure 7). Only minor damage

was done to the under side of the specimen.

NMNH 3509, 17 kg, approximately 1 km north of

San Juan.

This large, completely crusted individual had been

found north of San Juan within a few hundred
NUMBER 5 13

FIGURE 7.-A 2.0-kg Allende individual (NMNH 3502) found

by local boy at edge of Rancho Blanco on 14 February 1969:

a, in place, b, enlarged view; scale bar, 2 cm.

meters of the main road (Route 45). It was reported to have made a small depression in the

ground and was recovered in three large fragments

and three small ones. The fragments fit together

neatly, reconstructing the original morphology.

Surprisingly little damage was done other than the

clean fractures through the body of the specimen.

It is an eight-sided polyhedron, five sides of which

were abraded by the soil. The fusion crust, however,

is essentially intact.

NMNH 3513, 138 g, approximately 200 m southwest of Rancho Blanco.

This is a completely crusted individual that is

unusually small for this area of the strewnfield.

It was purchased 15 February 1969.

NMNH 3514, 202 g, approximately 200 m southwest of Rancho Blanco.

A nearly complete individual that is small for this

area of the strewnfield. Probably less than 10 percent of the specimen is missing. It was purchased

15 February 1969.

NMNH 3511, 8.2 kg, approximately 200 m southwest of schoolhouse in San Juan.

The specimen was found in a plowed field near the

school in San Juan (Figure 8). It has a large broken

surface that is free of fusion crust, suggesting it

separated into two major portions after the terminal

point of its high-velocity flight. It was purchased

from the finder 16 February 1969.

NMNH 3527, 12.0 kg, approximately 0.7 km south

of San Juan.

This completely crusted individual was found undisturbed by Brian Mason about noon on 17 February 1969 (Figures 3 and 14). It was in a plowed

field, having penetrated the ground to approximately its own depth. One large piece (11.0 kg),

one small piece (1.0 kg), and several small fragments were removed from the hole.

NMNH 3528, 18.5 kg, approximately 0.5 km southsoutheast of Pueblito de Allende.

This specimen was found at the edge of the Rio del

Valle de Allende between Pueblito de Allende and

Santa Ana in late February 1969. It is a completely

crusted individual that landed undamaged in the

stream bed. It is the largest sample that we know

of that landed without breaking.

NMNH 3529, 33 kg, approximately 2 km northeast

of San Juan.

This specimen was found fragmented near the

main highway 2 km northeast of San Juan during

February 1969. The fragments were collected by

Manuel Gomez by purchase from residents of San

Juan. The largest fragment weighed 14 kg and five

other fragments were in the 1- to 5-kg range.

NMNH 3531, 9.3 kg, near Santa Ana.

An excellent, completely crusted individual found

near Santa Ana. It was presented to the Smithsonian

Institution 16 February 1969 by Mr. and Mrs. R. C.

Byrd of Parral.

NMNH 3681, 281 g, near Porvenir.

A fragment purchased in late May 1969 near Porvenir. The owner reported that it was part of the

50-kg individual found earlier in the Sierra

Almoloya.

NMNH 3682, 617 g of fragments, near El Cairo.

This collection of small fragments was purchased
14 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

FIGURE 8.—An 8.2-kg Allende individual (NMNH 8517) found approximately 200 m southwest

of schoolhouse (white building) in San Juan: a, finder with Manuel G6mez, kneeling, and Cesar

Gallardo, right, examining hole from which specimen had been recovered earlier, b, photograph

of specimen; scale bar, 2 cm.
NUMBER 5 15

near El Cairo in late May 1969. The owner reported they were part of the 50 kg individual found

earlier in the Sierra Almoloya.

NMNH 3935, 1.8 g, Torre6n de Mata-Rancho

(ruinas) area.

An unusually small, completely crusted individual.

One surface of the specimen is a late break covered

with light fusion crust. Purchased in June 1969.

NMNH 4006, 540 g, in riverbed directly north of

Cienega de Ceniceros de Abajo.

This platy specimen is unusually large for this area

of the strewnfield (Figure 20). Purchased in June

1969.

NMNH 4015, 41 g and 39 g, in Cienega de Ceniceros de Abajo.

These two specimens were both recovered within

the town, one on a rooftop and one from a patio.

They were purchased in June 1969.

NMNH 4289, 2 g, near Cienega de Ceniceros de

Arriba.

A completely crusted individual found in zone 1 to 2

km north to 1 to 4 km south and southwest of

Cienega de Arriba. Purchased during June 1969.

NMNH 4646, 4.36 kg, approximately 1.5 km east

of Rancho Blanco.

This completely crusted large individual was found

near Rancho Blanco—an area that had been intensively searched from the date of fall—in mid-June

1969. It was purchased within a day or two of the

date it was found.

NMNH 4651, 26 g, from an area 1 to 3 km south of

Rancho Blanco.

This completely crusted individual is an unusually

small specimen for this part of the strewnfield. It

was purchased in early June 1969.

NMNH 4655, 4.7 kg, at south edge of San Juan.

This completely crusted individual was found in

the stream at the south edge of San Juan on Sunday,

8 June 1969. It was purchased shortly thereafter.

NMNH 4789 to 4799, 11 small specimens, tail of

strewnfield.

These specimens were found in 1.5 km2 area southwest of airstrip at tail of strewnfield. Eight of the

specimens were completely crusted individuals,

ranging in weight from 7.2 to 16 g. They were collected by Jack R. Hyde and local helpers in June

1969.

NMNH 4801 to 4809, 8 small specimens, tail of

strewnfield.

These specimens were found in a 3 km2 area to the

southwest of the group above, at the extreme end of

the strewnfield. Seven of the specimens can be considered complete individuals, and they range in

weight from 3.1 to 43 g, with an average weight of

10 g. If the 43 g specimen is rejected, the average

weight is 5 g. These specimens were collected by

Jack R. Hyde and helpers in June 1969.

NMNH 5183, 1.1 g, near the Ceniceroses.

This is the smallest completely crusted individual in

our collection. It is from a large group of specimens

collected by a single person within an area 4 km

to the northeast of Cienega de Ceniceros de Arriba

and Abajo extending 4 km to the south. This specimen was among a group purchased in November

1969.

NMNH 5240, 697 g, 4 km south of Valle de

Allende.

This specimen was found during the first week of

November 1969 partially buried in a field. It is a

major part of an individual with one large fracture

surface and fairly large areas where the fusion crust

had spalled. Areas of the specimen that were unprotected by fusion crust and protruding from the

ground were covered with a fine-grained white material tinged with blue and green. X-ray powder

diffraction analysis showed that this material was

largely hexahydrite (MgSO4*6H2O). This specimen

was purchased from its finder in November 1969.

NMNH 5268, 1.5 kg, south edge of Pueblito de

Allende.

This specimen was found on 15 November 1969 on

the south edge of Pueblito de Allende in the mud

at the side of an irrigation ditch. It has large areas

that were unprotected by fusion crust and apparently not buried completely in the mud. These

areas are heavily covered with a coating of finegrained white material tinged with blue and green.

X-ray powder diffraction analysis showed this material may be mainly hexahydrite (MgSO4'6H2O).

This specimen was purchased in mid-November

1969.

OTHER METEORITES FROM THE PARRAL—JIMENEZ

AREA.—Mexico is a country well-known for its many

meteorite finds (Fletcher, 1890; Farrington, 1915;
16 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

TO CAMARGO

and CHIHUAHUA

METEORITES OF THE

PARRAL-JIMENEZ AREA, CHIHUAHUA

MEXICO

A LOCATION OF METEORITES

0 3 10 15 20 25 30

FIGURE 9—Location of meteorites of the Parral-Jimenez area of Chihuahua, Mexico. The Allende meteorite fell between

two of the largest iron meteorites known, Morito and Chupaderos.

Buchwald, 1968). Three out of the ten largest

individual meteorite masses known are from Northern Mexico, and two of these, the Morito and Chupaderos irons, are from the Parral-Jim£nez area of

southern Chihuahua. The Allende meteorite, the

largest stony meteorite yet observed, fell in between

these two ancient falls, seemingly attesting to the

"peculiar property, difficult of explanation which

the Mexican soil has in attracting meteoritic" material (Barcena, 1876).

Morito is a single 11-ton conical mass of iron, a

medium octahedrite (IIIA), known as early as

1600. It was found on Rancho El Morito (approximate location of find, latitude 27°OO/N, longitude

105°28/W) and at an early date moved to Hacienda

San Gregorio (Figure 9). It has since been moved
NUMBER 5 17

to Mexico City and is preserved there in the School

of Mines. The three Chupaderos irons are medium

octahedrites (HIB) that have been known for centuries (Figure 9). The two largest masses, 14 and

6.5 tons, were found on the east slope of the Sierra

de Chupaderos (approximate location of find, latitude 27°10/N, longitude 104°4(KW). The probable

site of find of the Morito meteorite and the site

of the two Chupaderos masses are separated by approximately 85 km. A third mass of the Chupaderos

meteorite is the "Adargas" specimen (Buchwald,

1968). "Adargas" is a 3.4 ton mass that was moved

at an early date to La Concepci6n (Figure 9),

possibly coming originally from the area of the

Sierra Las Adargas.

The Parral—Jimenez area is undoubtedly among

the richest meteorite-producing areas in the world.

Within the relatively small area of approximately

4,000 km2, three of the world's major meteorites

have been recovered: the 11-ton Morito iron, the 24

tons of Chupaderos irons, and several tons of the

Allende stony meteorite. The area per meteorite

find for North America as a whole is 30,000 km2,

many times the area of recovery of the MoritoAllende-Chupaderos meteorites.

The place-names used in our map (Figure 9)

are all taken from the modern base maps described

above. Important names relating to the history of

the Morito and Chupaderos irons have changed in

a number of instances since the early reports and

maps were prepared. Jimenez or Ciudad Jime'nez

was known earlier as Huejuquilla (an Indian name,

pronounced Wa-hu-ke-yah), and a number of variations on this spelling have been used. Valle de Allende was previously known as El Valle de San

Bartolome", and simply as El Valle. The Rio del

Valle de Allende has been known as Rio de Allende

and Rio de San Bartolome". The Rio la Chona has

been referred to as the Rio de la Concepcidn.

Three other meteorites are listed in the literature as coming from the Parral-Jime*nez area:

Parral, Tule, and Sierra Blanca (Hey, 1966). All

three of these meteorites have recently been examined by V. F. Buchwald (personal communication, 1969) as part of his comprehensive examination of iron meteorites. Buchwald reports that Parral appears to be a fragment of Morito, Tule is a

pseudometeorite, and Sierra Blanca may be a transported fragment of the Toluca shower.

Morphology

The individual Allende meteorite specimens preserve in their ablation crusts and gross morphology

a partial record of the meteoroid's passage through

the atmosphere. This information, combined with

the observed specimen distribution pattern (discussed above), allows us to derive a probable sequence of events. The meteoroid entered the atmosphere at a low angle as a single large body with

cosmic velocity (greater than 11 km/sec, and probably less than 18 km/sec, McCrosky et al., 1969).

Friction between it and the increasingly dense atmosphere produced ablation and initiated the luminous fireball stage. Continued penetration into the

atmosphere was followed by a major disruption—

an explosion of the parent body—at a relatively

great altitude. Many large blocky fragments were

produced, as were smaller pieces and a quantity

of rubble. Each individual fragment continued in

luminous, ablative flight until reaching its point

of atmospheric retardation, the point at which its

cosmic velocity was completely dissipated. During

this part of the flight, fragments were subjected to

differential atmospheric drag depending on their

shape and orientation, resulting in size sorting along

the trajectory and lateral broadening of the cluster.

It was during this interval between initial disruption and retardation that fragments became individual crusted meteorite specimens. The recovery of

numerous specimens with areas of secondary fusion

crust indicates at least minor fragmentation and

spallation subsequent to initial breakup. Specimens

reached their individual retardation points and

then continued to the ground in free fall. It was

undoubtedly during the free-fall portion of their

descent that wind became a significant factor in

distorting the symmetry of the field (Figure 2) . The

largest specimens traveled the farthest and shattered

on impact, making small holes in the ground, while

small specimens generally fell far behind, producing

no damage and being recovered unscathed. Largeto medium-size specimens were recovered between

the two extremes, their condition on recovery depending on such factors as preexisting weakness in

the specimen and whether it landed on hard or soft

ground. Many remarkably fragile features ablated

on Allende meteorite fusion crust survived descent.

Individual stones are typically ablation-modified
18 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

fragmental shapes; blocky, pyramidal, and occasionally lenticular. They are covered with a dull

black fusion crust that tends to be chipped or

spalled awav at edges, revealing either fresh fracture surfaces or fracture surfaces covered with a

light secondary fusion crust that is frequently reddish in hue. The fusion crust contains occasional

lustrous spots above the calcium and aluminum-rich

aggregates which are characteristic of the meteorite,

and infrequent sooty areas above fine-grained black

inclusions. The amount of aerodynamic shaping of

FIGURE 10.—A 11.4-kg blocky, crusted Allende individual

(NMNH 3523) found between Pueblito de Allende and San

Juan. Scale bar, 5 cm.

an individual fragment is related to the stability of

its orientation during ablative flight. A small percentage of the individuals shows evidence of oriented

flight and heavy ablation both in the gross shape

of the specimen and in the character of fusion-crust

development on anterior and posterior surfaces. A

particularly curious feature of Allende specimen

morphology is the presence on five specimens of

hollow filaments of fusion crust encapsulating an

as yet unidentified material, apparently a colorless

hydrocarbon. In the following section individual

specimens that illustrate many of these features will

be described.

NMNH 3523, 11.4 kg, found between Pueblito de

Allende and San Juan.

This large, blocky specimen was purchased in Pueblito de Allende on 16 February 1969. Its fragmental

shape appears to be relatively unmodified by ablation, but its surfaces are essentially covered with a

well-developed fusion crust (Figure 10). Spalling

has occurred along edges, and many of these spalled

areas are partially or completely covered with a

thin reddish secondary fusion crust that does not

show clearly on the photographs. One fairly large

fragment appears to have broken off at a late stage,

leaving a fresh fracture surface (Figure 10c). Inclusions in the matrix revealed on this fracture

surface appear to have a parallel alignment, an
NUMBER 5 19

FIGURE 11.—A 6.2-kg Allende individual (NMNH 3500) found approximately 700 m southwest of

Rancho Blanco. Scale bar, 5 cm.

alignment that is also parallel to the top and bottom

exterior surfaces in this photograph (Figure 10c).

This suggests that the fracture pattern of the rock

may well be related to its internal fabric. The

lower part of Figure 106 shows the effect of colliding with the ground. Light-colored clay soil is embedded in the fusion crust, but the crust survived

essentially intact. At the upper part of the lightcolored area a well-developed polygonal craze pattern is emphasized by soil filling small cracks. This

surface craze is observed on specimens recovered

very soon after they fell, but is much more pronounced on some specimens that have been exposed

to the elements for a few months.

NMNH 3500, 6.2 kg, found approximately 700 m

southwest of Rancho Blanco.

This large specimen was purchased in Rancho

Blanco on 14 February 1969. It is a fragmental shape

only slightly modified by atmospheric ablation; a

rectangular base, two trapezoidal sides, and triangular ends (Figure 11). The rectangular surface is

indicated in profile in Figure \\b. Several of the

surfaces are slightly convex, and they are all covered with a well-developed fusion crust. Spalling

of fusion crust at edges, a common feature in

Allende specimens in general, is particularly pronounced on this stone.

NMNH 3501, 4.3 kg, found approximately 2 km

southwest of Rancho Blanco.

This complete individual was purchased in Rancho

Blanco on 14 February 1969. It is a nine-sided figure,

comprising three triangular and six trapezoidal

surfaces (Figure 12), suggestive from certain aspects

of a distorted octahedron (Figure 12a). Its flat surfaces are all heavily crusted, but there are relatively numerous areas of spalled crust at edges.

Most of these spalled areas are covered with a thin

reddish secondary fusion crust. The apex area in

Figure 12a is covered with this very thin crust that
20

is obvious to the unaided eye, but does not show

at all on these black and white photographs.

NMNH 3494, 7.0 kg, found 3 to 4 km south of

Rancho Santa Ana.

SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

This specimen (Figure 13) was found at the base

of a cactus plant on 13 February 1969 (Figure 6).

It is an essentially completely crusted individual, a

fragmental shape relatively unmodified by ablation.

FIGURE 12.—A 4.5-kg Allende individual (NMNH 3501) found approximately 2 km southwest of

Rancho Blanco. Scale bar, 5 cm.

FIGURE 13.—A 7.0-kg Allende individual (NMNH 3494) found at base of cactus 3 to 4 km

south of Rancho Santa Ana. See Figure 6. Scale bar, 5 cm.
NUMBER 5

There are three large trapezoidal surfaces and a

small one at the specimen's apex. A section perpendicular to these surfaces would be essentially

triangular. The corner and bottom surface in Fig21

ure ISa shows the part of the specimen that penetrated the ground on landing. Only slight damage

to the specimen seems to have resulted. Fusion

crust appears to have spalled off of most of the

FIGURE 14.—An unusually large oriented Allende individual (NMNH 3527). Found in place approximately 0.7 km south

of San Juan (see Figure 3), broken into 1.0-kg and 11.0-kg pieces: a, anterior surface to right, zone of fusion-crust accumulation diagonally from left to right, and posterior surface to left; b, anterior surface; c, posterior surface and zone of fusioncrust accumulation; d, posterior surface and zone of fusion-crust accumulation. Scale bar, 5 cm.
22 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

edges of the specimen, and most of the spalled areas

have a thin coating of secondary fusion crust. One

surface (Figure 13b) has a large area of spalled

fusion crust, the edges of which have this secondary

coating. The large surfaces in Figure 13a have welldeveloped flow lines in thick crust.

NMNH 3527, 12.0 kg, approximately 0.7 km south

of San Juan.

This large individual was recovered in two pieces

from a plowed field, buried to its own depth, by

Brian Mason on 17 February 1969 (Figures 3 and

14) . It is of particular interest because it is an unusually large oriented individual with spectacular

fusion-crust development. The specimen's basic

shape is a distorted pyramid with one domed surface. All of the photographs in Figure 14 show the

specimen sitting on the same surface. Figure 14a

was taken looking down on the specimen, showing

the edge of the anterior (upper right) and posterior

(lower left) surfaces. Figure \4b is of the complete

anterior surface, while Figure \Ad shows much of

the posterior area. Figure 14c shows one side of the

posterior surface, a portion of the zone of fusioncrust accumulation, and an edge of the anterior

surface. The surface not shown is a posterior surface

also containing a zone of fusion-crust accumulation.

This specimen is essentially completely crusted, but

it does have a number of small areas where crust

spalled late in flight or where small fragments have

been removed. The 1-kg apex fragment fits securely

in place, leaving no doubt about the preimpact

shape of the specimen. The black anterior surface

(Figure 14fr) contains a number of small spalled

areas, most of which are covered with a thin coating

of reddish fusion crust. This anterior surface is

somewhat irregular, and thick vesicular fusion crust

has accumulated in depressions. A zone of the posterior surface along the edge of the anterior surface

is covered with a thick vesicular accumulation of

fusion crust (Figure \Aa,c,d). This zone has a

width of 6 cm in some areas and shows a distinct

flow pattern. The posterior surface (Figure 14c,d)

has a much thinner fusion crust that is lighter in

color than that on the anterior surface, having a

decided brownish hue. A polygonal craze pattern is

pronounced on this thinner crust.

NMNH 3522, 188 g, found approximately 2 km

north of Torreon de Mata.

This unusually fine aerodynamically shaped specimen was purchased in Torre6n de Mata on 16 FebFIGURE 15.—An aerodynamically shaped Allende individual

found near Torre6n de Mata (NMNH 3522): a, side view of

anterior surface showing cone shape; b, looking down on

anterior surface; c, posterior surface with vesicular fusion

crust. Natural size, ammonium-chloride smoked to enhance

detail.
NUMBER 5

ruary 1969. It appears to have entered upon independent flight in the atmosphere as a plate-shaped

fragment. Orientation was maintained and aerodynamic sculpturing smoothed forward edges and

produced a cone-shaped specimen with pronounced

anterior and posterior sides (Figure 15, ammoniumchloride smoked). Flow lines in the fusion crust

fan out from the apex of the cone, and inclusions

within the meteorite produced a patchy appearance

due to varying crust composition (Figure 15 a,b).

The outline of chondrules produced a pronounced

pattern on the anterior surface, and small depressions in this surface developed areas of vesicularity.

A sharp boundary marks the edge of the anterior

and posterior surfaces, with fusion crust accumulating preferentially on the posterior surface near its

* --:-. •

FIGURE 16.—An aerodynamically shaped Allende individual from the area of the Ceniceroses (NMNH 4018): a, looking down

on anterior surface; c, posterior surface with fusion-crust accumulation at edges; b and d, side views showing flow of fusion

crust. Scale bar, 2 cm.
24 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

edge. The posterior surface is uneven, undoubtedly

a result of initial fragmentation. It is completely

covered with a highly vesicular fusion crust that is

somewhat thinner toward the center of the surface.

Fusion crust in general on the posterior surface is

considerably thicker than on the anterior surface.

NMNH 4018, 121 g, found in an area extending 4

km south and southeast of the Ceniceroses.

This specimen resulted from aerodynamic shaping

of a blocky fragment (Figure 16). It has a domed

anterior surface, four lateral surfaces, and a flat

posterior surface. Two of the corners of the back

surface are nearly right angles, the other two being

less regular. A fairly large area of fusion crust at

the apex of the dome has spalled, as have several

smaller areas of crust at edges. One small spalled

area on the anterior surface has been partially

covered with a light coating of reddish secondary

fusion crust. Most of the white material on the

anterior surface is foreign matter due to contact

with the ground (Figure 16a). The fusion crust

on the forward surface is black with a slight suggestion of red in limited areas. The crust on the

posterior surface is well developed and markedly

different in appearance (Figure 16c). It is pockmarked and dark reddish-brown in color, not particularly vesicular. The pockmarks appear to be

remnants of large vesicles that have been distorted

by collapse and surface flow. On the lateral surfaces

there are two types of crust flowing over the posterior crust (Figure I6b,d). The reddish-brown

crust of the posterior surface served as an undercoat

for streamers of vesicular black crust flowing from

the anterior surface. There is a particularly marked

buildup of fusion crust at the edge of the posterior

surface (Figure 16c), resulting from flow along the

lateral surfaces. Small beads of black glass were

carried on to the posterior surface by airflow and

can be seen with moderate magnification near the

edge.

NMNH 4083, 165 g, found near cemetery 300 m

south of Cie"nega de Ceniceros de Arriba.

This specimen appears to have initially been a rectangular parallelepiped that has been modified by

oriented flight and one major late-stage fracture. It

has four distinct surface types; anterior, lateral,

posterior, and fracture. Figure 17 gives views of

FIGURE 17.—An aerodynamically shaped Allende individual

found near Cienega de Ceniceros de Arriba (NMNH 4083):

a, anterior surface; b, side view, showing streamers of fusion

crust at the edge of the anterior surface. Natural size, ammonium-chloride smoked to enhance detail.

ammonium-chloride smoked surfaces; (a) the anterior surface, and (b) the edge of the anterior

surface and a lateral surface. The anterior surface

is predominantly black in color with a suggestion

of red that is pronounced in the few small areas

where fusion crust has spalled. Aerodynamic flow

along the surface is recorded as stringers of glass

in the fusion crust (Figure 17a). A surface pattern

due to differential melting of chondrules and matrix

is evident. Figure 176 is of an edge of the anterior
NUMBER 5 25

FIGURE 18.—An aerodynamically shaped Allende individual found southwest of Cienega de Ceniceros de Abajo (NMNH 4084):

a, Anterior surface with spalled apex; b, vesicular posterior fusion crust. Ammonium-chloride smoked to enhance detail.

Scale bar, 2 cm.

surface and a lateral surface. The accumulation of

fusion crust marked by stringers of glass in the

photograph marks the edge of the lateral surface.

The fusion crust on the lateral surface below the

zone of accumulation is thinner and noticeably

redder in color. The posterior surface has a thin

fusion crust covering a relatively unmodified rough

fracture surface. The area in the lower left of Figure 17a is a late fracture surface, free of fusion

crust. There are areas on the posterior surface and

at edges where fusion crust has spalled late in highvelocity flight, and some of these are covered partially or completely with a light, reddish coating of

secondary fusion crust.

NMNH 4084, 87 g, found H/2 km southwest of

Cienega de Ceniceros de Abajo.

The basic shape of this specimen seems to have been

a somewhat irregular tetrahedron (Figure 18, ammonium-chloride smoked). One set of three surfaces

has been smoothed into an anterior surface of an

aerodynamically oriented individual (Figure 18a).

Its anterior and posterior surfaces are clearly defined by the character of their fusion-crust development. The anterior surface has fusion crust over

about half of its area, spalling late in flight having

removed fusion crust at the apex. Part of this area

is covered with a light, reddish secondary fusion

crust that is not revealed in the photograph. There

are several fresh fracture surfaces along the edge

joining the anterior and posterior surfaces (Figure

186). The posterior surface is highly vesicular and

has three unusual protruding bodies that appear

to be fusion-crust-covered large chondrules standing out in relief.

NMNH 4157, 15 g, found in area 1 to 4 km southwest to south of Cienega de Ceniceros de Arriba.

This initially small fragment was markedly shaped

by aerodynamic ablation (Figure 19). It is typical

of a number of small individuals recovered from

the strewnfield, generally south of the Torre6n de

Mata area and frequently south of the Ceniceroses.

It has a domed anterior surface (Figure 19a) and

irregular posterior surfaces (Figure 19b,c) reflecting the original fragmental shape of the specimen.

It is completely crusted with the exception of one

small area on a posterior edge. The fusion crust

on the anterior surface is comparatively thin, with

a number of fine cracks. Fusion-crust accumulations

developed at edges of the posterior surface due to

flow from the anterior surface. Accumulations of
26 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

FIGURE 19.—A small aerodynamically shaped Allende individual (NMNH 4157) found southwest of the Ceniceroses: a,

anterior surface; b, side view; c, posterior surface. Twice actual size.

vesicular glass are also marked in depressions in

the posterior surfaces (Figure 19b,c). The white

areas in Figure 19b and c are adhering foreign

matter.

NMNH 4006, 540 g, found in the riverbed directly

north of Cie*nega de Ceniceros de Aba jo.

This specimen is remarkably heavy compared to

others found so far south in the strewnfield. The

explanation is undoubtedly atmospheric drag, and

evidence from the specimen itself supports this suggestion. The specimen was undoubtedly initially

a platy fragment that presented to the atmosphere

an exceptionally large surface area in relation to its

mass (Figure 20). Fusion-crust development indicates clearly an anterior (Figure 20fr) and posterior

(Figure 20a) surface. Fairly large areas on two opposite lateral surfaces are recent breaks, completely

free of fusion crust (Figure 20c). These surfaces

demonstrate that the area presented to the atmosphere during high-velocity flight was certainly

somewhat greater than the area of the present

anterior surface. The edges of the anterior surface

that do not join recent fracture surfaces are rounded

(Figure 206), and flow lines within the fusion crust

on lateral surfaces indicate flow toward the posterior

surface. In several areas where lateral surfaces join

the posterior surface there are accumulations of

vesicular crust (Figure 20a) on the posterior surface. Fusion crust on the anterior surface is relatively thin and noticeably reddish in color. The

posterior-surface fusion crust is similar, but it is

spattered in streaks with a black lustrous glass, suggestive of snail tracks, undoubtedly derived from

areas of fusion-crust accumulation. The result is

that the posterior surface has a sheen that is not

noticeable on the anterior surface.

Of the specimens available to us from the area of

the Ceniceroses, less than 6 percent weigh more than

100 g, less than one percent more than 200 g, and

less than 0.1 percent more than 300 g. The four

heaviest specimens are: NMNH 4006, 540 g, discussed above, NMNH 4007, 272 g; NMNH 4533,

257 g; NMNH 4575, 232 g. Three of these (NMNH

4006, 4533, 4575) are aerodynamically shaped specimens with a large ratio of anterior surface area to

weight of specimen. This would appear to be a

clear demonstration of atmospheric sorting on the

basis of shape as well as on the basis of mass.
NUMBER 5 27

FIGURE 20.—An unusually large Allende individual (NMNH 4006) found near Cienega de Ceniceros de Abajo. The flat shape resulted in high drag and retardation: a, posterior surface;

b, anterior surface; c, broken surface on bottom side of b. Scale bar, 5 cm.
28 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

NMNH 3812, 46 g, found in zone 1 to 4 km southeast to north of the Ceniceroses.

This specimen is one of a group of five displaying an

unusual type of lustrous fusion-crust development

(Figure 21). The specimen has areas of normal

fusion crust (^30%), spalled areas that are partially covered with secondary fusion crust (~50%),

and areas of a black, lustrous, blistery appearing

crust. This lustrous crust appears in part to have

flowed over areas of regular fusion crust on to

spalled areas. At the edges of these areas of flow the

crust seems to have accumulated to a greater than

normal thickness, and it has a resinous appearance.

From areas such as this, crust material appears to

have been drawn out, forming straps that adhere to

or bridge across areas of spalled matrix surface,

jumping gaps from a few millimeters to a centimeter

in length (upper left in Figure 21a and right side of

Figure 216). These ropy straps are suggestive of

drawn taffy, and they frequently follow the edges

of concave spalled areas. Extending from these

straps are spines that are drawn out to delicate

filaments, frequently with nobby ends. Filaments

on this specimen are translucent and amber in color

when very thin, and apparently encapsulate a colorless hydrocarbon material.

NMNH 3813, 34 g, found in zone 1 to 4 km southeast to north of the Ceniceroses.

This is the most dramatic of the five specimens with

the type of lustrous fusion-crust development described above (NMNH 3812). In most respects, this

specimen is a typical small individual, much of its

surface being covered with ordinary and secondary

fusion crust or spalled areas (Figure 226). One end

of the specimen, however, is capped with lustrous

fusion crust (Figure 22a). Protruding from this

area is a spine reminiscent of an antler, extending

a full centimeter. It is amber in reflected light, but

light yellow and translucent when backlighted (Figure 22c). It is remarkable that features of this

delicacy survived landing, recovery by a local resident, and shipment to Washington.

NMNH 3814, 77 g, found in zone 1 to 4 km southeast to north of the Ceniceroses.

A large part of the surface of this specimen is free

of fusion crust (Figure 236), while other areas are

covered with a normal thick, and in part vesicular,

FIGURE 21.—One of a small group of Allende specimens with

an unusual, lustrous fusion-crust development. Found near

the Ceniceroses (NMNH 3812). Twice actual size.

fusion crust. About half of the surface of the specimen, overlying both spalled and crusted areas, is a

network of ropy straps of lustrous fusion crust (Figure 23d,e). In several places the ropy material has

lifted from the surface of the sample and can be

seen in silhouette. Figure 23a is an enlargement of

the area in the upper left of Figure 23b, and Figure

23c is an enlargement of an area in the upper right

of Figure 236.

Broken surfaces and surfaces with thin fusion

crust show abundant chondrules, usually about 1

mm in diameter, but sometimes much larger.

Broken surfaces of a single large fragment from a

33 kg individual are illustrated in Figure 24
NUMBER 5 29

FIGURE 22.-An Allende individual from the area of the Ceniceroses (NMNH 3813) with a horn

of lustrous, translucent fusion crust: a, b, twice actual size; c, horn at four times actual size.
30 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

FIGURE 23.—An Allende individual from the area of the Ceniceroses (NMNH 3814) with a network of ropy, lustrous fusion

crust over spalled and crusted areas. Scale bar 2 cm for b, d. e; 1 cm for a, c.

(NMNH 3529, found 2 km northeast of San Juan).

Irregular aggregates, white to pink in color and

sometimes lensoid in shape, up to several millimeters long, are common in the black matrix. Figure 24a illustrates a normal distribution of aggregates, while the reverse side of the same piece

(Figure 246) show a preferential accumulation of

aggregates and large chondrules. A large polished

surface from this same individual is shown in

Figure 25. Chondrules, aggregates, and a single large

dark inclusion (see below) are shown. This surface

would be considered representative if the dark inclusion were excluded. Present in both Figures 24

and 25 are indications of a vague oriented fabric

suggested by subparallel elongation of aggregates.

These elongations may represent an original flattening, or a secondary flattening produced by later

deformation.
NUMBER 5 31

FIGURE 24.—TWO views of broken fragment from a large Allende specimen (NMNH 3529): a, normal distribution of aggregates and chondrules. b, preferential accumulation of aggregates and large chondrules, and a vague oriented fabric. Actual

size.
32 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

FIGURE 25.—A polished surface of slice of a large Allende individual (NMNH 3529). Note large

dark inclusion at bottom of photograph. Actual size.

Mineralogy and Petrography

Allende is an unusually heterogeneous meteorite,

and a comprehensive description of its composition

and structure is thus a complex task. We propose to

treat it in terms of its major components, as follows:

(a) matrix; (b) chondrules; (c) irregular aggregates; (d) dark inclusions. It has a remarkably diversified mineralogy; a list of the minerals so far identified is given in Table 1.

Under the microscope, sections of normal thickness (0.03 mm) show numerous chondrules, mostly

0.5 to 2 mm in diameter, and less numerous irregular translucent aggregates of variable size, usually

a few millimeters in maximum dimension, in a

black opaque matrix. Point-counting on one section

gave the following results: chondrules, 34 volume

percent; aggregates, 9 percent; matrix, 57 percent.

As a section is reduced in thickness, the matrix
NUMBER 5

Name

Kamacite

Awaruite

CoDDer

Troilite

Pentlandite

Chromite

Spinel

Hercynite

Perovskite

Olivine

Enstatite

Clinoenstatite

Clinohypersthene ,

Diopside

Augite (fassaite) . .

Ferroaugite

Anorthite

Gehlenite

Grossular

Nepheline

Sodalite

Cordierite

TABLE 1.—Minerals in the Allende meteorite

Mineral location

Formula Matrix Chondrules Aggregates

(Fe,Ni) x

Ni8Fe x x

Cu x

FeS x x

(Fe,Ni)9S8 x x

FeCr2O4 x

MgAl2O« x

FeAl2O4

CaTiOa

(Mg,Fe)2SiO4 x x

MgSiO8

MgSiOs x

(Mg,Fe)SiO8 x

CaMgSi2O8

Ca(Mg,Al,Ti)(Al,Si)2O6 x

Ca(Fe,Mg,Al)(Al,Si)2Oa

CaAlaSi2O8 x

CaaAlaSiOr X

CaaAlaSisOoa

NaAlSiO* x

NaiAlgSiaOuCl x

Mg^USiBOw

X

X

X

X

X

X

X

X

X

X

X

X

X

33

becomes progressively more translucent, and at a

thickness of about 0.01 mm is seen to consist of

minute transparent equant crystals, interspersed

with a moderate amount of opaque material. X-ray

diffraction shows that the matrix consists largely

of iron-rich olivine (~50 mole percent Fe2SiO4).

Electron micrographs (courtesy Dr. K. M. Towe)

show that many of the minute olivine crystals are

idiomorphic, one to a few microns in greatest dimension (Figure 26).

Dispersed throughout the matrix is several percent of sulfides, present as pentlandite with occasional coarser grains of troilite. Localized sulfide

concentrations are frequently found at chondrule

edges, as are the larger grains of both pentlandite

and troilite. Areas of pentlandite and grains of

troilite sufficiently large for microprobe analysis

were examined. The nickel content of the pentlandite ranges between 16.5 and 21 percent, with an

average value around 19 percent, and about 0.7 percent cobalt is present. The troilite appears to be pure

FeS, without detectable nickel and cobalt. The rare

grains of metal are generally rich in nickel (67—68%

Ni and 1.6% Co by microprobe), although an occasional grain of low nickel kamacite was observed

within chondrules. These nickel-rich grains would

normally be described as taenite, but Dr. E. P. Henderson (personal communication) has noted that

the microhardness of these grains is notably and consistently less than that of taenite, and points out

that the composition is similar to that of awaruite.

Awaruite approximates the formula Ni3Fe and is

an ordered structure in contrast to taenite. Kullerud

and El Goresy (1969) note that awaruite is stable

below 503°C in the condensed Fe-Ni-S system, but

cannot coexist stably with troilite. Electron microprobe investigation established, however, that in the

Allende meteorite metal of awaruite composition
34 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

FIGURE 26.—Electron micrographs of Allende meteorite matrix, courtesy of Dr. K. M. Towe: a, transmission micrograph of

idiomorphic olivine crystal (x 68,000), with electron diffraction pattern (inset), b, c, platinum-carbon replica micrographs of

representative matrix grains, probably olivine ( x 30,000).
NUMBER 5 35

exists in intimate association with both pentlandite

and troilite. Other minerals included in the matrix

are minute amounts of chromite, native copper, and

possibly mackinawite (Dr. G. Kullerud, personal

communication). The carbonaceous matter cannot

be recognized as such except by the uniform black

coloring of the matrix; it probably exists as a thin

film coating the individual crystallites of olivine

and other minerals.

A remarkable variety of chondrules has been observed in this meteorite (Figures 28-34). They can

be divided into two groups (I and II) on the basis

of chemical and mineralogical composition, and

into many different textural types. The chemical

groups are:

I. Magnesium-rich chondrules. These consist of

magnesium-rich olivine, sometimes with clinoenstatite and interstitial glass (which may be partly

devitrified). Individual olivine crystals are frequently zoned, with cores of almost pure Mg2SiO4

and increasing iron content towards the surface.

An X-ray diffractometer trace shows a sharp peak

corresponding to a composition of Fa9, with a broadened base indicating some variation in composition.

The average of the microprobe analyses (100

points) is Fa6 (Figure 27), the commonest value

being Fao_i. The clinoenstatite is close to MgSiO3

in composition. Microprobe analyses of the glass

show that it is rich in calcium and aluminum; a

typical analysis is (weight percent) : SiO2, 47.8;

A12O3, 24.7; CaO, 17.5; MgO, 6.3; FeO, 0.7; Na2O,

2.0; K2O, 0.2. The chondrules usually consist entirely of silicate minerals. A few contain small

amounts of sulfides, which occasionally are present

as spherical aggregates. Some chondrules are rimmed

with small grains of sulfides.

A great variety of textures has been observed in

these chondrules. The commoner types can be

grouped as follows, in approximate order of

abundance:

1. Granular olivine (Figure 28). A tightly

packed aggregate of euhedral olivine crystals.

Within a single chondrule the individual crystals

are fairly uniform in size, but this size varies from

chondrule to chondrule; the range measured is

15 20 25

Mole Percent FeoSi0,,

30 35 4 0 45

FIGURE 27.—The composition of individual olivine grains in Allende chondrules, determine by

electron microprobe analysis.
36 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

from 0.02 to 0.5 mm in different chondrules. Some

chondrules have a core of coarse crystals and a

mantle of much smaller grains.

2. Granular olivine plus clinoenstatite. Like 1,

but containing minor amounts of clinoenstatite.

Frequently, the grains of clinoenstatite are concentrated near the surface of the chondrule and then

show a "snowball" effect, the clinoenstatite prisms

being arranged tangentially to the surface. Clinoenstatite crystals within the chondrules may be comparatively large and poikilitically enclose grains of

olivine.

3. Barred olivine chondrules (Figures 29, 30).

Long prisms of olivine are interspersed with bars

of glass or devitrified glass. The olivine prisms may

be parallel throughout the chondrule, may show a

fan-shaped arrangement, or may form two or more

nonparallel sets. Frequently, a barred chondrule

will have a mantle of olivine, which may be in

optical continuity with the core olivine.

4. Monosomatic olivine chondrules. These chondrules consist of a rounded single crystal of olivine,

usually about 0.5 mm in diameter; sometimes this

rounded single crystal is surrounded by an aggregate of small olivine grains.

5. Pyroxene-rich chondrules. These are rare in

Allende; this is reflected in the low content of

normative pyroxene, as shown by the chemical

analysis of a chondrule concentrate (Table 3, column 6, on page 45).

II. Calcium- and aluminum-rich chondrules. These

are comparatively rare, making up less than five

percent of the total chondrules, but show unusual

chemical and mineralogical compositions. Three

distinct types have been recognized, and probably

others remain to be discovered. The mineralogy

of the three types is as follows:

a. Gehlenite-fassaite-anorthite-spinel.

b. Anorthite-forsterite-spinel.

c. Nepheline-sodalite-fassaite-olivine.

FIGURE 28.—Irregular aggregates and chondrules in black matrix of the Allende meteorite;

diameter of the largest chondrule (granular olivine) is 1.4 mm. Transmitted light.
NUMBER 5 37

FIGURE 29.—Allende chondrule (0.7-mm diameter) of prismatic olivine crystals in dark glass,

with a halo of small olivine crystals. Transmitted light.

FIGURE 30.—Barred olivine chondrule with a narrow continuous rim of olivine in Allende

meteorite; diameter 1.2 mm. Transmitted light.
SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

FIGURE 31.—Three juxtaposed barred chondrules in the Allende meteorite, in transmitted (upper)

and reflected (lower) light; the reflected light photograph shows tiny sulfide grains (white) on the

surface of the chrondrules (largest chrondrule is 1.7-mm diameter).
NUMBER 5 39

FIGURE 32.—Allende meteorite granular olivine chondrule (1.3

mm diameter) in reflected light, showing two spherical sulfide inclusions.

Type a form prominent chondrules, being unusually large, one (Figure 33) measuring 24 mm in

diameter. This provided material for both bulk

chemical analysis (Table 3, column 7) and for

microprobe analyses of the individual minerals

(Table 2). Gehlenite is the most abundant mineral

(~40 percent), and is present as large prismatic

crystals; its refractive indices are « — 1.660,

€ = 1.655. The microprobe analysis shows that it

is close to pure gehlenite in composition, with a

moderate amount of the akermanite component

(Ca2MgSi2O7). Pyroxene forms about 30 percent of

the chondrule, and is an unusual type, being highly

aluminous and also titanium-rich; in terms of components, it contains about 59 percent CaMgSi2O6 by

weight, 24 percent CaAl2SiO6, and 17 percent

CaTiAl2O6. Its refractive indices are a = 1.705,

/? = 1.713, y = 1.735; it is colorless and nonpleochroic, in marked contrast to the purple titaniferous

clinopyroxene in the Angra dos Reis meteorite, and

in terrestrial igneous rocks. Dr. Joan Clark of the

United States Geological Survey has determined its

cell dimensions, with the following results (in A) :

a = 9.725±0.004; b = 8.828±0.003; c = 5.306

±0.003; p = 105°55'±10'; V = 438.1A3. Pyroxene

with a considerable content of the CaAl2SiO6 comTABLE 2.—Microprobe analyses of gehlenite, fassaite,

and anorthite in a large chondrule (type a, Figure

33) from the Allende meteorite (J. Nelen, analyst).

Values given in weight percent

SiO,

TiOa

Al,Oa

MgO

CaO

Gehlenite

27.0

0.1

27.7

3.1

41.0

Fassaite

39.8

5.5

18.2

9.7

25.4

Anorthite

43.4

0.1

35.8

0.0

20.2

98.9 98.6 99.5

Iron and sodium were looked for but not detected above the

trace level.

ponent is termed fassaite. Other minerals in the

chondrule are anorthite (about 10 percent), and

spinel (about 20 percent).

The composition of this type a chondrule is

closely similar to the compositions studied by Prince

(1954) in the CaO-MgO-Al2O3-SiO2 system. Using

his diagram for the 10 percent MgO plane in this

system, a melt of approximately the composition of

this chondrule would begin to crystallize spinel at

about 1550°C, followed by gehlenite at about

1400°C, anorthite at 1250°C, pyroxene at 1235°C.

The textural relations of these minerals in the chondrule are consistent with this sequence of crystallization. Small euhedral crystals of spinel are included

within all the other minerals. Gehlenite is present

as large prismatic crystals, suggesting crystallization

over a considerable temperature interval, whereas

the anorthite and fassaite occur as smaller xenomorphic grains in the interstices of the gehlenite crystals, and are evidently a late crystallization product.

A type b chondrule is illustrated in Figure 34.

This chondrule, 2 mm in diameter, consists largely

of prismatic crystals of anorthite, notably larger in

the outer part than in the core. Tiny crystals of

colorless spinel are included within the anorthite

crystals. A little forsterite, interstitial to the anorthite prisms, is present. The anorthite contains

about 0.5 percent Na2O, corresponding to about

5 percent of the NaAlSi3O8 component.

A single chondrule of type c has been found. It

was observed on a broken fragment of the meteorite,
40 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

FIGURE 33.—Gehlenite-anorthite-fassaite-spinel chondrule (type a) in the Allende meteorite, 24 mm in diameter; gehlenite is

the major phase and is present as large prismatic crystals, fassaite and anorthite occur as equant grains interstitial to the

gehlenite, and the spinel is disseminated as small crystals throughout the other minerals. Transmitted light.
NUMBER 5 41

FIGURE 34.—Anorthite-forsterite-spinel chondrule type b in the Allende meteorite (2.1-mm diameter); white prismatic crystals are anorthite, the spinel is finely dispersed throughout the chondrule,

and the forsterite is interstitial to the anorthite crystals. Transmitted light.

being unusually large (8 mm in diameter) and a

uniform chalky-white color. It is so fine-grained

that the individual minerals could not be identified

in grain mounts in immersion oils. X-ray powder

photographs provided positive identifications for

sodalite, nepheline, clinopyroxene (probably fassaite), and olivine, and this mineralogy is consistent

with the bulk chemical composition of the chondrule (Table 3, column 8). By the X-ray procedure

of Yoder and Sahama (1957) the composition of the

olivine was found to be Fa2e, in good agreement

with the FeO/FeO+MgO ratio in the chemical

analysis. This occurrence of sodalite (Na8Al6Si6-

O24C12, with 7.3 percent Cl), the first recorded from

a meteorite, is particularly intriguing, since the

chlorine content of stony meteorites is usually low

(of the order of 100 ppm) and combined as chlorapatite. Microprobe analyses have confirmed the

presence of nepheline and sodalite, and have provided some significant compositional data; in particular, potassium is notably fractionated between

the two minerals, the nepheline containing 1.5 percent K and the sodalite less than 0.1 percent. The

extremely fine-grained texture of this chondrule

suggests that it solidified as a glass and subsequently

devi trifled.

The calcium- and aluminum-rich chondrules frequently show narrow reaction rims against the

matrix, whereas the magnesium-rich chondrules do

not. This can probably be ascribed to the contrast

in composition between the calcium-rich chondrules

and matrix, whereas the magnesium-rich chondrules

are compositionally similar to the matrix. The occurrence of reaction rims implies that either the

chondrules or the matrix, or both, were quite hot

when the material aggregated.

A prominent feature of the Allende meteorite,

and one seen in few other chondrites, is the pres-
42 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

ence of irregular aggregates, white, pale gray, or

pale pink, usually up to a few millimeters in maximum dimension. Many of the aggregates are somewhat elongated or lensoid, and on large surfaces

there is a suggestion of subparallel arrangement of

the individual aggregates. Frequently the as^resrates

show narrow but distinct rims against the matrix;

these rims probably represent reaction zones with

the matrix.

Under the microscope these aggregates are seen

to be very fine-grained, the only prominent mineral

being rounded grains of pinkish spinel, which are

set in a microgranular aggregate of isotropic or

weakly birefringent material. X-ray diffraction, supplemented by chemical analysis, has elucidated the

mineralogy. A bulk analysis of one 250-mg aggregate

(Table 3, column 9) shows that it is composed essentially of calcium and magnesium alumino-silicates, the composition being comparable with the

gehlenite-anorthite-fassaite-spinel chondrules. These

minerals are also prominent constituents of the

aggregates. In addition, some of them contain nepheline and sodalite, their occurrence evidently being

conditioned by the presence of appreciable amounts

of sodium in these aggregates. Some aggregates contain considerable amounts of grossular, this mineral

also previously unrecorded in meteorites. The identification of grossular rests on its X-ray powder

photograph, giving a cell dimension of 11.85A,

identical with that of pure Ca3Al2Si3O12; it is

evidently too fine-grained to be recognized either

optically or with the microprobe, although it is certainly abundant in some aggregates. Fuchs (1969)

has described one aggregate consisting largely of

cordierite, with associated aluminous enstatite, anorthite, spinel, and sodalite. Marvin et al. (1970) have

identified spinel, hercynite, gehlenite, anorthite,

nepheline, diopside, fassaite, ferroaugite, and perovskite from these aggregates.

The presence of grossular has considerable significance in the interpretation of these aggregates.

Grossular is not known to crystallize from a melt;

it decomposes above 800°C into a mixture of wollastonite, gehlenite, and anorthite. Yoder (1954)

crystallized it from a glass of the requisite composition at 800°C. The extremely fine-grained nature

of the aggregates suggest devitrification of a glass,

and the presence of grossular indicates that this

devitrification took place in some of them at or

below 800°C.

On broken surfaces of the Allende meteorite one

occasionally sees small areas somewhat darker than

the enclosing matrix; these areas are fine-grained

and have no visible chondrules, in contrast to the

highly chondritic matrix (Figure 25). They are

usually angular in outline, and range in size up to

about 3 cm across. In thin section under the microscope these inclusions are seen to differ from the

surrounding material only in chondrule size; they

are essentially the same as the main mass of the

meteorite except that the chondrules are much

smaller, ranging up to 0.5-mm diameter, and are

somewhat sparser; the same irregular aggregates

are also present. The overall similarity is confirmed

by a chemical analysis (Table 3, column 4), which

is not significantly different from that of the bulk

meteorite. An X-ray diffractogram shows good olivine peaks indicating a composition of Fa48, the

peaks however being somewhat skewed towards

lower Fa values.

FUSION CRUST.—A unique feature of the Allende

meteorite is the lustrous fusion crust discussed above

in the section on morphology (Figures 21-23). This

type of crust covers both spalled surfaces and areas

of normal fusion crust, indicating that it developed

late in the individual stone's passage through the

atmosphere. Its translucency and amber color led

us to assume first that it was a silicate glass of unusual eomposition. One of our specimens (NMNH

3811) was sectioned on this basis for microscopic

and electron microprobe investigation. It was a

great surprise to learn from preliminary examination of these sections that this strange crust actually

consisted of a thin film of silicate fusion crust encapsulating comparatively large volumes of a material tentatively identified as a hydrocarbon. Our

main supporting evidence for this identification is

semiquantitative electron microprobe analysis indicating that this "hydrocarbon" contains approximately 85 percent carbon and no other elements detectable by the microprobe. It contains less carbon

than graphite and considerably more carbon than

the plastic mounting medium used in preparation

of the section. The material is essentially colorless

and is very soft, suggestive of paraffin. Until definitive work can be done, we will refer to this material

as a hydrocarbon.
NUMBER 5 43

FIGURE 35.—A mosaic of photomicrographs of a polished thin section through

lustrous fusion crust, NMNH 3811. A 5-mm length of sample edge is revealed;

transmitted and reflected light.

Figure 35 is a mosaic of low-magnification photomicrographs of one of the polished thin sections

through lustrous fusion crust, revealing a 5-mm

length of sample surface. Lustrous fusion crust

overlies all but the extreme right edge of the area

shown. The area of fusion crust at the right of the

photomicrograph is lustrous material extending out

from the meteorite matrix approximately 0.2 mm

and bridging it for a distance of 1 mm. Smaller

areas are seen to the left, and in places this lustrous

crust thins to the point where it cannot be distinguished from the edge of the matrix. It is, however, continuous under higher magnification. The

outer edge of this crust assemblage is a thin film

of silicate glass containing a few matrix fragments

and heat-precipitated magnetite. The glass is too

thin to be seen in the photomicrograph, ranging in

thickness from 10 to 30 microns. Underneath the

outer glass layer is a region of hydrocarbon material

that may be continuous with the matrix, or may

adhere to the glass crust, but be separated from the

matrix by voids. The rim seen in the photograph

consists largely of hydrocarbon material colored by

a thin film of dark glass lying mainly below the surface of the section.

The lustrous fusion crust spine protruding at the

left side of Figure 21a detached itself from specimen

NMNH 3812 during the course of this preliminary

investigation, providing material from a second

stone for examination. A longitudinal section was

prepared that yielded a trough-shaped volume of

sample with a surface 4 mm long and from 0.5 to 1

mm wide, ranging from 0.2 to 0.5 mm in depth,

with a total volume of hydrocarbon material of

approximately 0.8 mm3. The total volume of hydrocarbon in this one spine prior to loss of material

during section preparation was certainly greater
44 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

than 1 mm3. The glass crust surrounding this volume was similar in thickness to that noted above,

from 10 to 30 microns, accounting for probably

less than 10 percent of the total volume. If this

small fragment and the sections from specimen

NMNH 3811 are representative of lustrous fusion

crust in general, a large concentration of apparently

indigenous hydrocarbon material is present.

The source of the hydrocarbon material concentrated under the crust of specific Allende stones is

an intriguing problem. Bulk carbon analyses

(Table 3) indicate that essentially all of the carbon

in Allende is associated with matrix material and

dark inclusions, average values of several analyses

being 0.36 and 0.37 percent respectively. Work in

other laboratories has yielded some indirect information on the nature of the carbon-containing compounds in the Allende meteorite (Han et al. 1969;

Or6 and Gelpi, 1969; Ponnamperuma et al., 1970;

Levy et al., 1970). These workers agree that Allende

contains negligible quantities of solvent-extractable

organic substances. Oro and Gelpi (1969) have reported, however, that direct volatilization or pyrolysis, or both, of Allende meteorite produces 10 to 20

ppm of a complex mixture of predominantly aromatic hydrocarbons with smaller amounts of aliphatics

and other compounds. This result is confirmed by

Ponnamperuma et al. (1970). The conclusion of

Han et al. (1969) that an upper limit of 0.1 parts

per billion of possible indigenous organic matter in

Allende seems unwarranted, and our observation

of organic matter concentration within fusion crust

suggests a possible alternative to terrestrial contamination as a source of some of the organic material

they found in surface samples.

The mechanism by which large quantities of organic material are concentrated under the fusion

crust of specific Allende stones presents a second

intriguing problem. The work on pyrolysis of Allende material suggests that volatile organic compounds may have been formed by pyrolysis during

ablation. A portion of this material would be expected to be lost to the atmosphere, while a part

of it would be driven into the porous meteorite. A

steep temperature gradient with depth into the

stone would account for condensation and accumulation of volatiles slightly below the molten surface. This zone of accumulation would move into

the meteorite as ablation progressed, concentrating

volatiles from large volumes of pyrolized (ablated)

meteorite. When ablation stopped and the interior

of the sample warmed, the organic accumulation

would expand and flow under the hardening crust,

producing features similar to the observed morphology (Figures 21-23). If 10 to 20 ppm organic

product is realistic for this natural pyrolysis process,

one would expect something of the order of 100 g

of meteorite to be consumed or heated by the ablation process for each milligram of organic material

accumulated. This seems excessive in terms of the

observed accumulations of several milligrams on a

small surface and leads us to wonder if these particular stones were not associated with inclusions richer

in volatile-producing compounds than normal

Allende material.

Chemical Composition

Chemical analyses have been made of two samples

of the bulk meteorite, a dark inclusion, the matrix,

a concentrate of chondrules, two individual chondrules, and a single aggregate. These results are

reported in Table 3.

Two different pieces were selected for the bulk

analysis. The first, 81 g (NMNH 3509), contained

several white aggregates; the second, 45 g (NMNH

3511), appeared more homogeneous. The samples

were ground in a tungsten-carbide mortar to pass

100 mesh. Several metallic grains larger than 100

mesh—totaling, however, less than 0.01 percent of

the sample—remained on the sieve. A split of each

sample was then analyzed for major and minor

constituents, following the general procedure outlined in an earlier paper (Jarosewich, 1966). The

two analyses are in excellent agreement with the one

exception that the first sample has somewhat more

A12O3, undoubtedly due to the presence of white

aggregates.

Noteworthy features of the bulk composition of

the Allende meteorite are the minute amount of

free metal, the presence of most of the nickel as

sulfide (a microprobe test of sulfide-free matrix

showed no detectable nickel in the silicates), the

high content of A12O3 and CaO (about 50 percent

greater than in the common chondrites), and the

low values for Na2O and K2O (about half that in

the common chondrites). The analysis is very similar
NUMBER 5 45

TABLE 3.—Analytical data on the Allende meteorite (E. Jarosewich, analyst). Values in weight percent

unless otherwise indicated

1

Bulk Analyses

Average Dark

of 1 & 2 Inclusion Matrix

6 7 8 9

Chon- Chon- Single

Chon- drule drule Aggredrules (Type a)* (Type c)5

 gate9

NMNH Cat. Nos. 3509 3511 3509 3510 3510 3529 3509 3510

SiOa

TiOs

A12O8

CrsO8

FeO

MnO

MgO

CaO

NasO

K8O

P,O6

HSO(+)

HaO(_)

C

Cl

FeS1

NiS1

CoS1

Fe

Ni 1

Co1

Total

D(g/cm8)

Total Fe

1 0 0 Fe O

FeO + MgO

34.20

0.16

3.36

0.51

27.22

0.18

24.50

2.65

0.44

0.03

0.23

0.00

0.29

n.d.a

3.98

1.64

0.08

0.15

0.32

0.01

99.95

23.85

34.26

0.14

3.18

0.53

27.09

0.18

24.75

2.57

0.45

0.03

0.23

<0.1

0.00

0.29

n.d.

4.08

1.56

0.08

0.19

0.40

0.01

100.02

23.84

34.23

0.15

3.27

0.52

27.15

0.18

24.62

2.61

0.45

0.03

0.23

0.00

0.29

4.03

1.60

0.08

0.17

0.36

0.01

99.98

3.65

23.85

38

33.42

0.13

2.56

0.56

31.48

0.26

23.91

3.00

0.34

<0.01

0.31

n.d.

0.00

0.37

n.d.

1.95

2.26

0.06

n.d.

n.d.

n.d.

100.61

n.d.

25.71

42

33.11

0.13

3.07

0.55

29.68

0.22

21.42

2.67

0.44

0.03

0.25

n.d.

0.00

0.36

n.d.

5.49

1.05

0.09

0.40

0.85

0.02

99.83

n.d.

26.56

44

41.87

0.26

5.57

0.47

9.44

0.14

34.34

4.06

0.82

0.06

0.11

n.d.

0.00

0.00

n.d.

1.78

0.87

0.03

n.d.

n.d.

n.d.

99.82

n.d.

8.47

13

29.79

0.99

31.61

0.06

0.37

0.02

10.82

26.76

0.11

0.00

0.00

n.d.

0.00

0.06

n.d.

0.00

0.00

n.d.

n.d.

0.03

n.d.

100.62

3.25

0.29

40.2

0.12

17.8

0.2

8.8

0.1

15.2

5.3

10.6

0.6

n.d.

n.d.

n.d.

0.02

2.0*

n.d.

n.d.

n.d.

n.d.

0.05

n.d.

100.6

 s

2.80

6.82

25

33.7

1.3

26.6

0.1

2.3

0.0

13.1

21.6

1.1

0.05

0.0

n.d.

n.d.

n.d.

n.d.

n.d.

n.d.

n.d.

n.d.

0.06

n.d.

99.9

3.18

1.76

n.d. = not determined

1

 Calculated on basis of microprobe data for metallic phase: 68% Ni, 31% Fe and 1.6% Co. Metallic Fe was determined

chemically and metallic Ni and Co assigned on basis of analysis given above. Remainder of Ni and Co were calculated as

sulfides. The remaining S was calculated as FeS.

2

 M. Quijano-Rico, Max-Planck-Institut, Mainz, determined Cl by neutron activation, obtaining 224 ppm in bulk sample

and 1.5% in chondrule type c. The difference between the 1.5 and 2.0% value is undoubtedly due to our use of a gravimetric

method with a very small sample (33 mg).

'Total of 100.99 corrected by 0.45, the Cl = 0.

4

 1.5 g sample weight.

6

 0.31 g sample weight.

6Gast et al. (1970) reported the following results on a similar inclusion (all in ppm): K 96.4, Rb 3.5, Sr 180, Ba 47.3,

La 4.63, Ce 11.5, Nd 8.40, Sm 2.82, Eu 1.30, Gd 3.87, Dy 4.90, Er 3.44, Yb 3.96.
46 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

to that of the Efremovka meteorite (Jarosewich

and Mason, 1969), except that Efremovka has about

7 percent nickel-iron and correspondingly less iron

combined in the silicates.

The analysis of the dark inclusion was performed

on a 1.3 g sample. As pointed out above, it is

closely comparable with that of the bulk material

of Allende, and it is very similar to the analysis

of Mokoia (Wiik, 1956), which is another Type III

carbonaceous chondrite.

The analyzed material of the matrix, and the

chondrule concentrate, were prepared by carefully

crushing and sieving a number of fragments of the

meteorite. Gentle crushing releases a large amount

of the matrix in the form of fine dust which passes

through a 325-mesh screen, and a sample of this

was used for the analysis (2.9 g). The chondrules

were concentrated in the —10 —|— 30 mesh fraction

(approximately 0.6-2.0 mm diameter), a 1.5 g sample being obtained. The analyzed chondrules were

not entirely free from matrix; the FeO/FeO-f-MgO

molecular percentage in the analysis is 13, so the

average for the chondrules themselves will be considerably less.

The composition of the matrix is not markedly

different from that of the bulk meteorite, which is

reasonable, since matrix forms about 60 percent by

volume of the meteorite and somewhat more by

weight. The matrix clearly contains most of the

metal and sulfide phases. The FeO/FeO-|-MgO

molecular percentage of 44 is consistent with the

average fayalite percentage (50) in matrix olivine,

since the matrix fraction contains other minerals

(calcium aluminum silicates and spinel) with low

FeO/FeO-f-MgO ratios.

The composition of the chondrule concentrate

shows marked contrasts with that of the matrix,

particularly in total Fe content, MgO content, and

in FeO/FeO-j-MgO molecular percentage. This of

course reflects the fact that most of the chondrules

are made up largely of forsteritic olivine, with minor

amounts of clinoenstatite. The calcium-rich chondrules account for the somewhat higher CaO and

A12O3 contents. Sulfides are notably lower in the

chondrule concentrate; they usually occur on the

surfaces of the chondrules, but are sometimes enclosed within them. Metallic nickel-iron was observed both in matrix and in chondrules.

The aggregates and the calcium-rich chondrules

present the most marked chemical contrasts to the

rest of the meteorite. They contain up to ten times

the amount of calcium and aluminum (and titanium) as in the meteorite as a whole. They are quite

unlike any composition that has yet been recorded

from stony meteorites. The composition is also

quite unlike any terrestrial rocks, except for some

rare calcsilicate hornfels, such as that described by

Knopf and Lee (1957). The nearest analogy is to

some blast-furnace slags. The composition given by

the analysis of the type a chondrule corresponds

to the low-melting region in the CaO-MgO-Al2O3-

SiO2 system, and the association anorthite-gehlenite-fassaite-spinel is consistent with crystallization

of a melt of this composition. The origin of such a

melt from meteoritic matter, however, presents

certain problems. Both calcium and aluminum are

minor elements in average chondritic matter, being

present at about the 1 percent level. One procedure

for enriching them is the removal of large amounts

of magnesium as olivine and clinoenstatite; neither

of these minerals incorporates appreciable amounts

of calcium and aluminum. This can be seen from

the composition of the glass in the magnesium-rich

chondrules, quoted earlier, although this glass is

somewhat richer in SiO2 than the calcium-rich chondrules and aggregates. The composition of the single aggregate analyzed is rather similar to the type a

chondrule, except for a much higher sodium content, expressed in its mineralogy by the presence

of nepheline and sodalite. The type c chondrule has

a very distinctive composition, marked by high

sodium and potassium (about twenty times that

in the bulk meteorite), and a remarkable chlorine

content, more than fifty times that in the bulk meteorite. These extreme fractionations pose some intriguing questions regarding the processes involved

in the formation of such chondrules, presuming the

parent material was essentially undifferentiated. In

this connection it is probably significant that anorthite, gehlenite, and spinel are among the first

solids to condense from a gas of cosmic composition.

Larimer and Anders (1970) have convincingly

argued for chemical fractionations in meteorites by

addition or removal of early formed phases. They

find that under the probable conditions within the

cooling solar nebula MgAl2O4 condenses first at

1470°K, followed by Ca, Ti, and Al minerals. At
NUMBER 5 47

1350°K Mg2SiO4 begins to condense, followed by

MgSiO3 and nickel-iron at 1300°K. The presence of

spinel, anorthite, gehlenite, and fassaite as chondrules and aggregates in Allende and other Type III

carbonaceous chondrites indicates that this class of

meteorites owes some of its unique characteristics

to the incorporation of this early formed condensate.

COMPARATIVE CHEMICAL DATA.—Additional chemical

data on the Allende meteorite are given in Tables

4 and 5. Table 4 lists concentrations for a number

of trace elements determined by spark source mass

spectrometry. In Table 5 our chemical data are

compared with the published data of King (1969);

Emery et al. (1969), Morgan et al. (1969), and

Wakita and Schmitt (1970). In general, agreement

between workers and the various techniques represented is excellent. The work reported by Emery

et al. contains several discrepancies, however, perhaps due either to unrepresentative sampling or

inadequate methods. Table 5 also contains data on

elements that we have not determined.

TABLE 4.—Trace element data on the Allende

meteorite1

Values in parts per million

B 1 Y ..

Sc 11 Zr .

V 70 Nb

Cu 100 Mo

Zn ...... . 25 Sn .

Ga 7 Sb .

Ge 15 Ba .

As 2 La .

Br 0.5 Ce .

Rb 0.9 Pr .

Sr 13

2 Nd 0.9

9 Sm 0.5

0.9 Eu 0.1

2 Gd 0.6

0.7 Tb 0.09

0.2 Dy 0.6

5 Ho 0.1

0.7 Er 0.3

1 Yb 0.4

0.2 Pb 1

Elements detected but not of suitable intensity for measurement, or suitable standards were lacking.

Se, Ru, Rh, Pd, Ag, Cd, In, I, Te, Cs, Tm, Hf, W,

Re, Os, Ir, Pt, Au, Tl, Bi, Th, U.

Hg was not detected.

Ta could not be confirmed because of possible contamination from spark stand.

Lu could not be determined because it was used as an

internal standard.

1B. Mason and A. L. Graham, analysts. Determinations

made by spark-source mass spectrometer while B. Mason

was a Visiting Research Fellow in the Department of Geochemistry, Australian National University, Canberra, 1969.

Gast et al. (1970) have reported on several trace

elements in a calcium-rich inclusion in Allende.

Their values are given in a footnote to our bulk

analysis of one of these inclusions (Table 3).

Discussion

The classification of the Allende meteorite presents

some interesting problems. Visual inspection immediately suggests that it is a carbonaceous chondrite, specifically a Type III as defined by Wiik

(1956) —it is closely similar to others of this type

such as Vigarano and Mokoia. Chemical and mineralogical examination confirms this similarity. It

has the Si/Mg ratio characteristic of the carbonaceous chondrites, and it falls within the range of other

Type III meteorites (Figure 36). The conjunction

of iron-poor olivine in chondrules with iron-rich

olivine in matrix is also distinctive for these meteorites. Yet the carbon content (0.3 percent) is low

for a carbonaceous chondrite, lower in fact than

in a number of chondrites whose Si/Mg ratio places

them in the ordinary (bronzite and hypersthene)

classes.

Recently Van Schmus and Wood (1967) have

provided a revised classification for the chondrites,

based on a two-dimension grid combining chemical

composition and textural and mineralogical features. They divide the carbonaceous chondrites into

four types, designated Cl, C2, C3, and C4. Types

Cl, C2, C3 include the same meteorites as Wiik's

Types I, II, III, except that Kaba and Mokoia are

considered C2 rather than Type III. This produces

some ambiguity in the classification of Allende,

since it is very similar to Mokoia in chemical and

mineralogical composition; however, separating Mokoia and Kaba from the other C3 chondrites seems

poorly based, since both these meteorites belong

with the other Type III carbonaceous chondrites in

terms of bulk chemical composition. Their matrix

consists largely of iron-rich olivine, whereas in

Type II-C2 chondrites the matrix is hydrated magnesium-iron silicate (serpentine or chlorite). Wiik's

classification appears more suited to the carbonaceous chondrites than that of Van Schmus and Wood.

Whereas the latter classification seems well adapted

for the other classes of chondrites, its application to

the carbonaceous chondrites presents certain inconsistencies—probably because the sequence Cl to C4
48 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

for the carbonaceous chondrites reflects different

conditions of genesis than the E3-E6, H3-H6,

L3-L6, and LL3-LL6 sequences for the other classes

Van Schmus-Wood classification are known only

in the carbonaceous chondrites; their absence in

the other chondrite classes suggests a fundamental

of chondrites. Significantly, types 1 and 2 in the genetic difference.

16 18 20 22 24

Mg 0, weight per cent

26 28
NUMBER 5 49

Van Schmus (1969) has recognized two distinct

subtypes of the C3 chondrites, provisionally called

the Vigarano and the Ornans subtypes. He writes:

"The most obvious distinction between the subtypes is textural. The chondrites belonging to the

Vigarano subtype may be characterized as having

large (1-2 mm diameter) 'spongy' chondrules embedded in an abundant, fine-grained, opaque matrix; 'spongy' chondrules contain numerous spheroidal droplets of nickel-iron or sulfide dispersed

through the silicate chondrule. The chondrites

belonging to the Ornans subtype may be characterized as a close-packed aggregate of small (0.2-0.5

mm diameter) metal-poor chondrules with finegrained, opaque matrix packed between the chondrules."

The distinction is a useful one, and can usually

be easily made by visual inspection. The Vigarano

subtype (designated A in Table 6) has large prominent chondrules in a black or dark gray matrix,

whereas the Ornans subtype (B) has an evenly

granular texture of close-packed chondrules and a

uniform light- or medium-gray color. The chemical

analyses of the different meteorites show a close

similarity for the major components, and for many

of the minor and trace elements; carbon, however,

is quite variable, as is H2O-|- (the H2O-(- reported

in the chemical analyses is probably not combined

water but H (and O) combined with carbon in an

organic complex—unweathered meteorites of this

type do not contain hydrated minerals, and H2O-fis generally correlated with carbon content). The

recorded densities show a considerable range for

a group of meteorites of rather uniform composition. Some of this range can perhaps be ascribed

to the difficulties of determining accurate densities

of porous and fine-grained material; however, the

higher densities are characteristic of subtype B meteorites, which generally have an appreciable content

(up to 5 percent) of free nickel-iron, whereas subtype A meteorites usually have little or no free

nickel-iron and a larger content of carbonaceous

material.

FIGURE 36.—SiO2 plotted against MgO (weight percentages) for chemical analyses of chondrites;

the diagonal lines are for Si/Mg atomic ratios of 1.0 and 1.1. A is the field for 36 analyses of

bronzite chondrites, B the field for 68 analyses of hypersthene chondrites, the black squares

being the means for each group. The analyses of carbonaceous chondrites (-}-) and enstatite chondrites (•) are plotted individually, as follows:

Type I

1.

2.

3.

Alais

Orgueil

Ivuna

Type II

4.

5.

6.

7.

8.

9.

10.

11.

Nawapali

Boriskino

Cold Bokkeveld

Erakot

Mighei

Murray

Santa Cruz

AlRais

Type III

12.

13.

14.

15.

16.

17.

18.

Grosnaja

Kaba

Vigarano

Lance

Karoonda

Mokoia

Ornans

19. Renazzo

20. Felix

21. Efremovka

22. Coolidge

23. Warrenton

Y. Allende (bulk analysis)

Z. Allende (black inclusion)

Enstatite

Chondrites

24. St. Sauveur

25. Indarch

26. AdhiKot

27. St. Marks

28. Abee

29. Atlanta

30. Daniel's Kuil

81. Hvittis

32. Khairpur

33. Blithfield

34. Jajh deh Kot Lalu
50 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

TABLE 5.—Comparison of chemical data on the Allende meteorite. (Values in

percent unless noted, ppm = parts per million, ppb — parts per billion)

Element King1

Emery

et al?

Morgan

et al?

Wakita and

Schmitt *

This

Work

O .

Si .

Ti .

Al .

Cr .

Mn

Mg

Ca

Na

K .

C ..

Ni .

Co

Fe .

B .

Sc .

V .

Rb

Zr .

Cd

In .

Cs .

Ba .

Hf

W .

Ir .

Pt .

Au

U .

La .

Ce .

Pr .

Nd

Sm

Eu

Gd

Tb

Dy

Ho

Er .

Tm

Yb

Lu

Y

15.9

0.11

1.75

0.42

0.13

14.5

1.8

0.30

0.025

0.27

1.41

0.070

23.6

0.010

0.017

0.006

0.001

34.7

15.9

1.35

0.42

0.17

13.1

1.88

0.18±0.12

1.15

0.06

27.8

10 ppm

^0.7 ppm

19 ppb

35.9±0.7

15.81 ±0.35

0.39±O.l

0.33+0.01

1.43±0.09

684±17 ppm

612±54 ppm

24.4±0.4

12.2±0.2 ppm

12.0±0.7 ppm

0.16±0.02 ppm

0.15±0.02 ppm

0.71 ±0.03 ppm

1.8±0.2 ppm

0.26±0.01 ppm

1.71 ±0.05

3680±100 ppm

1450±40 ppm

2.0±05

337O±1OO ppm

640±20 ppm

21.9±0.4

11.0±0.5 ppm

130±10ppm

1.3±0.1 ppm

0.19±0.01 ppm

0.027±0.001 ppm

0.06±0.01 ppmB

0.44±0.02 ppm

1.25 ±0.06 ppm

0.20±0.01 ppm

0.91 ±0.05 ppm

0.29±0.01 ppm

0.107 ±0.005 ppm

0.43±0.02 ppm

0.074±0.O05 ppm

0.42±0.02 ppm

0.12±0.01 ppm

0.31 ±0.02 ppm

0.049±0.001 ppm

0.32±0.02 ppm

0.058±0.002 ppm

3.0±0.1 ppm

[36.6]*

16.00

0.09

1.73

0.36

0.14

14.85

1.87

0.33

0.02

0.29

1.39

0.06

23.85

1 ppm

11 ppm

70 ppm

0.9 ppm

9 ppm

5 ppm

0.7 ppm

1 ppm

0.2 ppm

0.9 ppm

0.5 ppm

0.1 ppm

0.6 ppm

0.09 ppm

0.6 ppm

0.1 ppm

0.3 ppm

0.4 ppm

2 ppm

•Oxygen by difference.

1

 King (1969).

a

 Emery et al. (1969).

8

 Morgan et al. (1969).

* Wakita and Schmitt (1970).

6

 Changed from published values, Schmitt, personal communication (1970).
NUMBER 5 51

TABLE 6.—The Type HI carbonaceous chondrites

Name

Weight

Date of fall recovered, kg D(g/cms) %C

Allende (Mexico)

Bali (Cameroon)

Coolidge (Kansas)

Efremovka (U.S.S.R.) .

Grosnaja (U.S.S.R.) .. .

Kaba (Hungary) ..... .

Leoville (Kansas)

Mokoia (New Zealand)

Vigarano (Italy)

Felix (Alabama)

Kainsaz (U.S.S.R.) .. .

Karoonda (Australia)

Lance (France)

Ornans (France)

Warrenton (Missouri)

Subtype A or Vigarano subtype

8/2/1969

22/12/1907

find

find

28/6/1861

15/4/1857

find

26/11/1908

22/1/1910

>2000

3?

4.5

21

3.5

3

8.1

5

16

3.65

3.58

3.53

3.53

3.49

3.40

3.48

3.55

3.42

0.29

0.56

0.19

0.76

0.56

1.99

0.77

0.75

1.15

Subtype B or Ornans subtype

15/5/1900

13/9/1937

25/11/1930

23/7/1872

11/7/1868

3/1/1877

3

>200

42

52

6

50?

3.78

3.76

3.57

3.64

3.61

3.64

0.64

0.61

0.10

0.58

0.35

0.30

The Si/Mg ratio is slightly lower in the Type III

carbonaceous chondrites than in the ordinary chondrites, and the FeO content is considerably higher.

This has far-reaching consequences, since the bulk

composition is now very undersaturated with respect

to SiO2, so much so that feldspathoids appear in

place of feldspar. Specifically, sodium in the common chondrites is present as sodic feldspar (NaAlSi3O8, with about 10 percent of the CaAl2Si2O8

component), whereas in Allende (and probably in

other chondrites of this group) sodium is present

as the NaAlSiO4 component (nepheline), and the

feldspar is calcic, being almost pure CaAl2Si2O8.

It has always been something of a puzzle why feldspar composition in stony meteorites is remarkably

quantized, being sodic plagioclase in the common

chondrites and calcic plagioclase in most achondrites, intermediate compositions (common in terrestrial rocks) being essentially unknown in meteorites. Possibly this segregation of sodium and

calcium into distinct phases in the Allende meteorite is a clue to the solution of this puzzle.

The Allende meteorite is noteworthy as being the

largest of the carbonaceous chondrites yet recovered.

As such, it offers an unequaled opportunity for a

thorough investigation. Our work has emphasized

the significance of the contrasts between matrix,

chondrules, and aggregates. These peculiar aggregates are certainly the most intriguing feature. The

larger ones (those readily visible to the naked eye)

are not uniformly distributed through the meteorite,

being certainly more prominent in some specimens

than others. Similar aggregates have been noted in

other Type III carbonaceous chondrites. Sztr6kay

et al. (1961) noted them in the Kaba meteorite, but

because of scarcity of material they were not closely

investigated. Michel-L^vy (1968, 1969) has described

mineralogically similar aggregates from the Vigarano and Lancd meteorites. We have observed them

in the Bali meteorite. The meteorite which resembles Allende most closely, however, is Leoville.

Only a brief abstract describing this meteorite

has so far appeared (Keil et al., 1969), but conversations with Professor Keil and inspection of specimens of Leoville confirm the remarkable similarity.

Especially significant is the presence of numerous

white aggregates in Leoville, essentially similar in

chemical and mineralogical composition to those

in Allende.
52

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•ft U.S. GOVERNMENT PRINTING OFFICE: 1970 O—40O-O8B