Allan Hills A76004 meteorite, Allan Hills, Victoria Land, Eastern Antarctica, Antarcticai

Regional Level Types
Allan Hills A76004 meteorite	Meteorite Fall Location
Allan Hills	Group of Hills
Victoria Land	Region
Eastern Antarctica	Region
Antarctica	Continent

Unequilibrated ordinary chondrite, breccia (LL3,br; S2; W1)
Found, 1976-1977; 305 g, several pieces

Allan Hills A76004 was discovered during the austral summer of 1977-78. Although the meteorite is quite small it turned out to be one of the more petrographically and mineralogically diverse of the Antarctic meteorites recovered during the first meteorite hunting expeditions of the late 1970's. Under a somewhat weather-rounded fusion crust was a very dark gray matrix which contained a plethora of chondrules, fragments, glass, and irregular clasts — plus some diverse inclusions several cm in diameter. Chondrules [usually < 2 mm in diameter] are mainly porphyritic olivine [PO] and porphyritic olivine-pyroxene [POP], but several other types are also present. A large proportion of compound and elongated, plastically deformed chondrules are present. The range in olivine (Fa 0-34) and Ca-poor pyroxene (Fs0-53) composition is unusually large. Variable anorthic plagioclase and several varieties of silicate glass are present as well. In reflected light Fe-Ni metal and sulfides are also visible (~5 vol%). The metallic grains are often found in assemblages rimmed by troilite. Preliminary investigations revealed a number of additional phases in the chondrules, matrix, and/or inclusions (opaques, phyllosilicates, other silicates…). Shock indicators (shock level S2) include undulose extinction in olivine as well as the deformed chondrules. Weathering is relatively light (W1) with some limonite stains and small veins.

A cosmic ray exposure age of ~25 Ma is reported.

Names and abbreviations of Antarctic Meteorites: In the early 1980's a convention was fixed of using 3 letter abbreviations for Antarctic meteorites instead of the 4 letters used here. This convention did not alter the names and official abbreviations for the meteorites recognized before this time. However, one also sees — for example — 'Allan Hills 76004' and 'ALH 76004' in some of the formal scientific literature.

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