Sample No.: ALHA77278

Location: Allan Hills

Field No.: Y78010601

Weight (gms): 312.9

Meteorite Type: LL3 Chondrite

Physical Description:

Sample ALHA77278,0 is moderately rounded. Approximately 95% of the surface is covered by a dull black fusion crust (with exception of the B surface) that is ~1-2 mm thick. The fusion crust on the B (posterior) surface is reddish, shows well-developed radial flow lines, and is more oxidized than the other surfaces. Several spots, i1 cm diameter, where the fusion crust has been plucked, reveal interior material that is light gray and moderately iron-oxidized. This appears to be a complete specimen, whose dimensions are ~8.0x5.5x4.5 cm. A freshly chipped surface reveals a small amount of metal and appears relatively unweathered. This stone appears to be a low petrologic type.

Petrographic Description: Brian Mason

The meteorite consists of a close-packed aggregate of spherical to ellipsoidal chondrules (0.3-1.8 mm diameter) with interstitial nickel-iron and troilite (concentrated as rims to chondrules) and relatively little matrix. Most chondrules consist of granular or porphyritic olivine, sometimes accompanied by polysynthetically-twinned clinopyroxene, and with partly devitrified glass between the mineral grains. Microprobe analyses show that both olivine and pyroxene are variable in composition; olivine ranges from Fa11 to Fa29, with a mean of Fa24, and pyroxene is low-calcium (Ca=0.1-0.4%) with Fs ranging from 9 to 21 and a mean of 12.  Some unusual enclaves were noted in the polished thin section. One, 1.5 mm across, consisted of numerous small (max. 0.2 mm) grains of olivine and pyroxene in a brown-black semi-translucent matrix, possibly carbonaceous. Another, 3 mm long, consisted of an aggregate of olivine (composition Fa13-Fa26) and orthopyroxene (Fs16-17) grains with a little interstitial turbid glass. The section shows a slight amount of yellow-brown limonitic straining, concentrated near the fusion crust.