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Allan Hills A77005
Basic information Name: Allan Hills A77005
     This is an OFFICIAL meteorite name.
Abbreviation: ALHA77005
This meteorite may also be called Allan Hills 77005 (ALH 77005) in publications.

Observed fall: No
Year found: 1977
Country: Antarctica [Collected jointly by ANSMET (US) and NIPR (Japan)]
Mass:help 483 g
Classification
  history:
Antarctic Meteorite Newsletter:  AMN 1(2)  (1978)  Achondrite
AMN 1(3)  (1978)  Achondrite-unique
AMN 7(1)  (1984)  Shergottite
Meteoritical Bulletin:  MB 76  (1994)  Shergottite
NHM Catalogue:  5th Edition  (2000)  Martian (shergottite)
NIPR Catalogue:  2000 Edition  (2000)  Shergottite
MetBase:  v. 7.1  (2006)  Shergottite-lherzolitic
Recommended:  Martian (shergottite)    [explanation]

This is 1 of 171 approved meteorites (plus 1 unapproved name) classified as Martian (shergottite).   [show all]
Search for other: Martian meteorites
Writeuphelp
Writeup from AMN 4(1):

Sample No.: ALHA77005

Location: Allan Hills

Field No.: 77122928

Weight (gms): 482.5

Meteorite Type: Achondrite (unique)

 

Physical Description:

The specimen is well rounded on all faces except the south face, which is a partially broken surface. A well developed, dark fusion crust randomly covers approximately 5% of the meteorite's surface in small, thin patches. Parts of the stone are covered by a vitreous crust that possibly is the lower portion of the dark, outer fusion crust, which has been physically abraded. Some partially melted crystals are in contact with this glassy rind. The specimen's dimensions are ~9.5 cm x 7.5 cm x 5.25 cm. The specimen is well-indurated and difficult to chip. This would be a good meteorite for the study of fusion crust. The outer dark crust has apparently been removed by physical weathering. There is little evidence that the glassy rind has been affected by chemical weathering. The thin section chip may not be representative of the entire specimen. On the cut surface the sample appears to be fresh. Variations in color of sawed surface suggest heterogeneities on a centimeter scale. Voids up to 2 mm in diameter are present on the sawed surface. Some of these voids show crystal structures on the peripheral surface, but they do not appear to extend into the cavity.

 

Petrographic Description: Brian Mason

This meteorite is an achondrite with the following modal composition (volume percent): olivine, ~55; pyroxene ~35; maskelynite, ~8; opaques (mostly chromite, a little ilmenite, trace amounts of troilite and nickel-iron), ~2. Olivine occurs as somewhat rounded anhedral to subhedral grains up to 2 mm long, and has an unusual pale brown color; microprobe analyses show a mean composition of Fa28. Pyroxene occurs as colorless prismatic crystals up to 6 mm long, often poikilitically enclosing olivine; some crystals show coarse polysynthetic twinning; the composition is somewhat variable averaging Wo5Fs23En72. Maskelynite is present as laths interstitial to olivine and pyroxene; it has labradorite composition (An53) and contains 0.2-0.3% K2O. The meteorite has been severely shocked, as is shown by the presence of maskelynite, undulose extinction in the pyroxene, and occasional areas of apparent shock melting. No signs of weathering were observed. Meteorite ALHA77005 is a unique achondrite. The olivine is comparable in composition to that is chassignites, the pyroxene to that in diogenites, and the bulk composition will thus be intermediate between these two classes of achondrites. However, these classes are almost plagioclase-free, and maskelynite of similar composition is known only from the Shergotty and Zagami achondrites; these meteorites are quite different from ALHA77005 in consisting largely of calcium-rich clinopyroxene and containing no olivine.

Data from:
  MB76
  Table 2
  Line 14:
Origin or pseudonym:Main icefield
Mass (g):482.5
Class:Sherg
Weathering grade:A
Fayalite (mol%):28
Ferrosilite (mol%):23
Comments:26Al=55±2
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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Photos:
CreditPhotos
Photos from the Encyclopedia of Meteorites:
Dr Carlton Allen, JSC-KT, NASA      
Geography:

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

Statistics:
     This is 1 of 38180 approved meteorites from Antarctica (plus 5051 unapproved names)
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