Sample No.: ALHA78019

Location: Allan Hills

Field No.: 274

Wight (gms): 30.3

Meteorite Type: Ureilite

Physical Description:

Fusion crust is present on all surfaces but is patchy and does not cover the entire stone. The fusion crust is smooth, dull brownish black and has polygonal fracture. Where the fusion crust is not present the surface is reddish-brown and crystalline. One fracture penetrated the entire stone. The stone (3.0 x 2.5 x 3.0 cm) was cleaved in half and no unweathered material was exposed. The entire sample is reddish-brown throughout. The interior is crystal-line which breaks apart when handled.

Petrographic Description: Brian Mason

The thin section shows an aggregate of rounded to subhedral grains (0.5 - 3 mm across) of olivine, with minor pyroxene. The grains are rimmed with black carbonaceous material. Trace amounts of troilite and nickel-iron are present, the latter largely altered to translucent brown limonite concentrated along grain boundaries. Microprobe analyses show olivine of uniform composition (Fa22) with notably high CaO (0.4%) and Cr2O3 (0.7%) contents; the pyroxene is a pigeonite of composition Wo10Fs18En72. This meteorite is a ureilite, with mineral compositions essentially identical to those in the Kenna ureilite (Geochim. Cosmochim. Acta, 40, p. 1430, 1976); it appears to be relatively unshocked compared to most ureilites.