Sample No.: ALHA81313

Location: Allan Hills

Weight (g): 0.5

Field No.: 1680

Dimensions (cm): 0.8 x 0.7 x 0.4

Meteorite Type: Shergottite (?)

Macroscopic Description: Roberta Score

The stone is dark in color. The interior was not examined because this small specimen was not chipped and the entire mass was made into a thin section.

Thin Section (,1) Description: Brian Mason

The section shows a granular aggregate (grains 1-3 mm in maximum dimensions) of colorless plagioclase (maskelynite) and pale gray, weakly pleochroic pyroxene with trace amounts of opaque minerals (nickel-iron, troilite, chromite). A vague impression of pyroxene-rich and plagioclase-rich layers is present, possibly suggesting a cumulate. The pyroxene appears to be an inverted pigeonite with small blebs of exsolved augite. Point counting gives the following volume percentages: pyroxene, 54; plagioclase, 46. Microprobe analyses show the maskelynite is essentially stoichiometric and fairly uniform in composition, average An93 (Na2O 0.6-1.4%, K2O 0.04). Orthopyroxene composition is also fairly uniform, (average Ca 2.7 Fe 38; Al2O3 0.4%, MnO 0.9%, TiO2 0.2%, Cr2O3 0.3%). Composition of a single augite bleb is Ca38Fe20. In texture and mineral compositions this meteorite closely resembles the Moama monomict eucrite (Meteoritics, 10, p. 101, 1975). However, the presence of maskelynite indicates that ALHA81313 may be classed petrographically as a shergottite rather than a eucrite.