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Allan Hills 84025
Basic information Name: Allan Hills 84025
     This is an OFFICIAL meteorite name.
Abbreviation: ALH 84025
Observed fall: No
Year found: 1984
Country: Antarctica [Collected by US Antarctic Search for Meteorites program (ANSMET)]
Mass:help 4.6 g
Classification
  history:
Antarctic Meteorite Newsletter:  AMN 8(2)  (1985)  Achondrite-unique
AMN 13(1)  (1990)  Brachina-like
Meteoritical Bulletin:  MB 76  (1994)  Brachinite
NHM Catalogue:  5th Edition  (2000)  Brachinite
MetBase:  v. 7.1  (2006)  Brachinite
Recommended:  Brachinite    [explanation]

This is 1 of 49 approved meteorites classified as Brachinite.   [show all]
Search for other: Brachinites, Primitive achondrites
Writeuphelp
Writeup from AMN 8(2):

Sample No : ALH84025

Location: Allan Hills

Weight (g): 4.6

Field No.: 1518

Dimensions (cm): 2 x 1.5 x .8

Meteorite Type: Achondrite (unique)

 

Macroscopic Description: Carol Schwarz

This fragment has thick fusion crust on all sides but one. That surface is greenish with shiny crystals. The interior consists mainly of yellowish and greenish olivine or pyroxene. There are a few small dark inclusions and several grains of salt deposit visible. The sample is very friable and seems to be somewhat weathered.

 

Thin Section (,4) Description: Glenn MacPherson

this unique meteorite is essentially a dunite; it consists of large (up to 1.5 mm) polygonal olivine crystals that are uniformly Fo67-68 in composition, with lesser pyroxene (Wo44 En46 Fs11) and sparse polygonal chromite grains. The texture is very uniform and polygonal-granular. Criss-crossing the meteorite are veins of troilite, within which are tiny globules of Ni-rich (about 30% Ni) metal. In many cases these sulfide veins are no more than trails of tiny sulfide grains that outline crystal boundaries and define (presumably) healed fractures within crystals. Only the larger and more continuous veins contain metal. Neither the olivine nor the pyroxene show significant undulatory extinction. A well-defined fusion crust encloses much of the area in the thin section, reflecting the small overall size of this meteorite. A very few fractures show slight staining by iron oxides, indicating that the meteorite has experienced only minor terrestrial weathering. This specimen most closely resembles Brachina in texture and mineralogy but, unlike Brachina, it is much more coarsely crystalline and contains no plagioclase. No pentlandite was found during the preliminary examination and, if this holds true after more detailed work, it would further distinguish ALH84025 from Brachina. The absence of plagioclase and orthopyroxene, and near-absence of metal except the minor amount in the veins, distinguishes ALH84025 from meteorites such as ALHA77081 and Acapulco.

Data from:
  MB76
  Table 2
  Line 991:
Origin or pseudonym:Far Western
Mass (g):4.6
Class:Brach
Weathering grade:A/Be
Fayalite (mol%):32-33
Ferrosilite (mol%):11
Catalogs:
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References: Published in Antarctic Meteorite Newsletter 8(2) (1985), 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::   (77° 1' 22"S, 157° 1' 37"E)
Note: the NHM and MetBase coordinates are 75.2 km apart

Statistics:
     This is 1 of 39173 approved meteorites from Antarctica (plus 5051 unapproved names)
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