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Allan Hills A77302
Basic information Name: Allan Hills A77302
     This is an OFFICIAL meteorite name.
Abbreviation: ALHA77302
This meteorite may also be called Allan Hills 77302 (ALH 77302) in publications.

Observed fall: No
Year found: 1977
Country: Antarctica [Collected jointly by ANSMET (US) and NIPR (Japan)]
Mass:help 236 g
Classification
  history:
Antarctic Meteorite Newsletter:  AMN 1(2)  (1978)  Achondrite
AMN 1(3)  (1978)  Eucrite
AMN 4(1)  (1981)  Eucrite-pmict
Meteoritical Bulletin:  MB 76  (1994)  Eucrite-pmict
NHM Catalogue:  5th Edition  (2000)  Eucrite-pmict
MetBase:  v. 7.1  (2006)  Eucrite-pmict
Recommended:  Eucrite-pmict    [explanation]

This is 1 of 339 approved meteorites classified as Eucrite-pmict.   [show all]
Search for other: Achondrites, Eucrites, and HED achondrites
Writeuphelp
Writeup from AMN 4(1):

Sample No.: ALHA77302

Location: Allan Hills

Field No.: 77123022

Weight (gms): 235.5

Meteorite Type: Achondrite (polymict eucrite)

 

Physical Description:

Specimen is angular to subrounded. A glassy, thin, black fusion crust covers ~70% of the surface. In places the fusion crust has been physically plucked away. Large cavities are randomly distributed on the surface of the stone. The material exposed in these circumstances is fresh and unweathered, showing feldspar cleavages. The E surface (orthogonal photo) has a large, ~2 cm, clast protruding. This clast could easily be removed. The clast has an obviously coarser grain size and darker color than the bulk meteorite. Plagioclase crystals on this surface are several mm long. The B surface (orthogonal photo) has an irregularly shaped clast that in specific areas is different in texture and color from the bulk meteorite. Specimen's approximate dimensions: 9.25x5.5x4.0 cm. This appears to be a complete stone. Several small interior and exterior chips were generated during chipping. The exposed fresh surfaces are light gray, much like the light colored patch described above. The sample contains a large clast, ~1.5x1.5 cm, which is darker gray than the comminuted groundmass. Additionally, there are several smaller inclusions which appear similar to the large clast. Numerous light inclusions ranging up to ~3 mm in maximum length were also exposed on the sawed surface. The meteorite appears to have suffered little, if any, weathering.

 

Petrographic Description: Brian Mason

This meteorite is a brecciated pyroxene-plagioclase achondrite (polymict eucrite). It consists largely of pigeonite (~60%) as brown grains up to 2 mm, and plagioclase (~35%) as colorless grains up to 4 mm, in a comminuted groundmass of these minerals. A little troilite (<1%) and rare minute grains of nickel-iron are present. Fusion crust rims part of the section. No evidence of weathering was seen. Microprobe analyses show a range of compositions in the pigeonite: Wo3-14, En32-56, Fs37-64; a few grains of subcalcic ferroaugite averaging Wo25En27Fs48 were also analyzed. Plagioclase ranges in composition from An75 to An94. The section contains a large (6 mm) fine-grained enclave of similar composition.

Data from:
  MB76
  Table 2
  Line 251:
Origin or pseudonym:Main icefield
Mass (g):235.5
Class:Eu "pm"
Weathering grade:A
Ferrosilite (mol%):37-64
Comments:NTL=7.7±0.7; 76005 pairing group
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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