Sample No.: ALHA78261

Location: Allan Hills

Field No.: 491

Weight (gms): 5.113

Meteorite Type: Carbonaceous Chondrite - C2

Physical Description:

This triangular sample (2.5 x 1.5 x 1.0 cm) is totally covered with thin, dull, black, polygonally fractured fusion crust, except along the edges where the fusion crust has abraded away. The matrix revealed in these areas is greenish-black and has small (<1 mm) rounded and irregular white clasts throughout. Small voids, as much as 1 mm in diameter, are present on two surfaces. Chipping of the specimen during processing revealed abundant rounded and irregular inclusions in the meteorite.

Petrographic Description: Brian Mason

The section shows numerous tiny grains (up to 0.1 mm) and irregular aggregates (up to 0.3 mm) of olivine and polysynthetically twinned clinopyroxene, and a few small chondrules, in a translucent isotropic olive-brown matrix. The section contains very little troilite as minute scattered grains, and a little nickel-iron as inclusions in the chondrules. Porous fusion crust up to 2.5 mm thick rims part of the section. Microprobe analyses show that both olivine and pyroxene have variable composition. Olivine ranges from Fa0 to Fa50, with an average of Fa6; it has a notable chromium content, Cr2O3 ranging from 0.3-0.6 weight percent. Pyroxene is generally close to clinoenstatite in composition, ranging from Fs1 to Fs8, with an average of Fs7. This meteorite is a carbonaceous (C2) chondrite, and shows a close similarity to ALHA77306.