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An MPOD Classic
from 17 November 2013

ALH 84025   contributed by AMN   MetBul Link

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4.6 grams.   Brachinite

Fall not observed. Found 1984 in Antarctica.

Location Map of Antarctic Falls

AMN writes:
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 Description (,4) - 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.

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RENAUT Patrice
 11/17/2019 8:08:46 AM
Thank you very much for sharing. Petrographic description is very interesting and clear. Crystals bondaries are very well defined and the mafic texture is spectacular !
Don Cracraft 2650
 11/17/2019 5:26:06 AM
Thank you for sharing. Very nice!
Bernd Pauli
 11/17/2019 4:44:32 AM
U. Ott et al. (1987) Noble gases in ALH 84025: Like Brachina, unlike Chassigny (abs. Meteoritics 22-4, 1987, 476).

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