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Allan Hills A77306
Basic information Name: Allan Hills A77306
     This is an OFFICIAL meteorite name.
Abbreviation: ALHA77306
This meteorite may also be called Allan Hills 77306 (ALH 77306) in publications.

Observed fall: No
Year found: 1977 or 1978
Country: Antarctica [Collected jointly by ANSMET (US) and NIPR (Japan)]
Mass:help 19.9 g
Classification
  history:
Antarctic Meteorite Newsletter:  AMN 1(1)  (1978)  C2
AMN 17(1)  (1994)  CM2
Meteoritical Bulletin:  MB 76  (1994)  CM2
NHM Catalogue:  5th Edition  (2000)  CM2
MetBase:  v. 7.1  (2006)  CM2
Recommended:  CM2    [explanation]

This is 1 of 505 approved meteorites classified as CM2.   [show all]
Search for other: Carbonaceous chondrites, Carbonaceous chondrites (type 2), CM chondrites, and CM-CO clan chondrites
Writeuphelp
Writeup from AMN 4(1):

Sample No.: ALHA77306

Location: Allan Hills

Field No.: 78010402

Weight (gms): 19.91

Meteorite Type: Carbonaceous Chondrite - Type C2

 

Physical Description:

Color: The color is a charcoal-gray with a slight olive-green cast. Weathering rind is 2.0-4.0 mm deep and of a lighter gray then the interior.

 

Interior: Interior is a fine-grained gray matrix with ~-2-3% light colored inclusions throughout groundmass. Inclusions are irregular in shape. No obvious chondrules are present BUT a few 0.1-0.2 spherical-shaped areas are present. These areas are lighter in color. No white veins were observed.

Fusion Crust: Crust is present on approximately 40-60% of the sample. Differential weathering has removed fusion crust in one large area. Remainder of fusion crust is cracked and broken, with furrows across specimen. Crust remaining stands above the interior of the specimen ≈0.5-1.0 mm. Selected areas of crust are vesicular and glassy. The specimen is remarkably free of limonite stain.

Post Chip: When the specimen was cleaved into two halves, a greenish-gray weathering rind was observed to have penetrated into the meteorite to a depth of ~l mm. The interior, non-weathered portion, of the meteorite is a dull, blackish-gray. Small vugs are randomly distributed throughout the meteorite. It was not possible to determine if crystals are present in the vugs.

 

Petrographic Description: Brian Mason

Examination shows that it is a C2 carbonaceous chondrite. Chondrules are sparse, small (up to 0.5 mm diameter), and poorly defined; most consist largely of granular olivine, and some contain small globular grains of nickel-iron. The bulk of the meteorite (80-90%) consists of opaque to translucent olive-brown matrix, the translucent material showing weak birefringence; an X-ray powder photograph shows that the matrix consists largely of a layer-lattice silicate, which by analogy with other C2 meteorites can be tentatively identified as a ferriginous chlorite. Scattered through the matrix are colorless birefringent grains, mostly olivine, up to 0.3 mm but usually less than 0.1 mm across. Rare grains of chromite are present in the matrix. A notable feature is the apparent absence of metallic sulphides. The meteorite is moderately porous, containing irregular voids up to 0.3 mm across; the specific gravity, 2.58, measured on a small fragment, is therefore probably somewhat lower than the true value. No evidence of weathering was seen, which suggests that the meteorite may be a recent fall.

Data from:
  MB76
  Table 2
  Line 255:
Origin or pseudonym:Main icefield
Mass (g):19.9
Class:CM2
Weathering grade:A
Fayalite (mol%):1-45
Ferrosilite (mol%):1
Catalogs:
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References: Published in Antarctic Meteorite Newsletter 4(1) (1981), JSC, Houston
Published in Meteoritical Bulletin, no. 76, Meteoritics 29, 100-143 (1994)
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Geography:

Antarctica
Coordinates:
     Catalogue of Meteorites:   (76° 43'S, 159° 40'E)
     Recommended::   (76° 43'S, 159° 40'E)

Statistics:
     This is 1 of 38937 approved meteorites from Antarctica (plus 5051 unapproved names)
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