Sample No.: ALHA77081

Location: Allan Hills

Field No.: 77122716

Weight (gms): 8.59

Meteorite Type: H? Chondrite

Physical Description:

The stone is angular to subrounded. Highly weathered, brownish-black through reddish-brown fusion crust, and remnants of fusion crust, cover approximately 50 to 70% of the meteorite's surface. One face is a broken surface that shows iron oxide staining and has a granular texture. The longest side of the sample is ~2.0 cm.

Petrographic Description: Brian Mason

The meteorite is an equigranular (grains 0.1-0.3 mm across) aggregate of approximately equal amounts of olivine and orthopyroxene, with minor amounts of diopside, plagioclase, nickel-iron, and troilite, and accessory chromite. Fusion crust is present along one edge. A moderate amount of yellow-brown limonitic staining is present, concentrated around nickel-iron grains. Microprobe analyses show the minerals are uniform in composition: olivine, Fa11; orthopyroxene, Wo1.7Fs11En87; diopside, Wo45Fs5En50; plagioclase, An15, with 0.8% K2O.  The classification of this meteorite presents difficulties. The structure is achondritic, but the mineralogical composition is similar to that of the common chondrites, which suggests that this meteorite may be a completely recrystallized chondrite. However, the composition of the olivine and orthopyroxene is intermediate between that for the bronzite (H) and enstatite (E) chondrites. The meteorite resembles some silicate inclusions in iron meteorites. This meteorite is identical in mineral composition and structure to Acapulco, a recent Mexican fall.