Sample No.: ALHA77307

Location: Allan Hills

Field No.: 78010702

Weight (gms): 181.3

Meteorite Type: Carbonaceous Chondrite - Type C-3

Physical Description:

The rounded specimen is covered with a dull black fusion crust 1-2 mm thick over post of the surface. Specimen is complete with the exception of one end where a fracture surface covers 1/8 of the specimen's total surface area. The fusion crust has polygonal fractures over most of the exterior surface. In a few places this fusion crust has been broken away revealing a black fine-grained matrix. Specimen shows several large fractures. On the surface neighboring one of these fractures there is a white material which may be an evaporite deposit. The side of the specimen that was in contact with the ice at the time of recovery is slightly reddish. Dimensions: 4.5 x 4.0 x 5.0 cm. Small, irregular white inclusions and several chondrules are apparent on a freshly broken surface.

Petrographic Description: Brain Mason

the section shows a closely-packed aggregate of mineral grains (up to 0.2 mm), mineral aggregates (up to 0.8 mm), and rather sparse small (0.1-0.5 mm) chondrules, set in a dark brown to black opaque matrix; the matrix makes up 40-50% of the section. The mineral grains, aggregates, and chondrules consist of olivine and polysynthetically-twinned clinopyroxene in approximately equal amounts. Microprobe analyses show that most of the olivine has forsterite composition, Fa_~1, with a few grains ranging up to Fa₃₀; the average for 30 grains is Fa₅. The pyroxene is mostly clinoenstatite, Fs_~l, but with a few more iron-rich grains. A little (1-2%) nickel-iron is present in the matrix as scattered grains, many partly altered to brown limonite. Fine-grained sulfide (~5%) is dispersed through the matrix. Fusion crust, 0.5 mm thick, is present along one edge of the section. The meteorite is a carbonaceous chondrite; an X-ray powder photograph shows that the matrix consists largely of olivine and pyroxene with some magnetite, which indicates a C3 classification.