Sample No.: ALHA81005

Location: Allan Hills

Field No.: 1422

Weight (gms): 31.4

Meteorite Type: Anorthositic Breccia

Physical Description: Roberta Score

This is an unusual looking sample! Flow marks are apparent on the exterior which is covered with a pitted, glassy, greenish-tan colored crust. Immediately underneath this crust, the surface is a "dusty" gray color. The interior consists of abundant angular clasts, which range in color from gray to white, set in a black matrix. The size of the clasts are as small as submillimeter and as large as 8 mm in diameter. The sample is very coherent. Some areas of oxidation were noted.  Dimensions: 3 x 2.5 x 3 cm.

Petrographic Description: Brian Mason

The specimen is a microbreccia of clasts (maximum dimension 4 mm) in a translucent to semi-opaque dark brown glassy matrix showing flow structure in places; clast:matrix ratio is approximately 40:60. The larger clasts are polymineralic, the smaller (less than 0.3 mm) may be individual mineral grains. The clasts consist largely of plagioclase, together with some pyroxene and occasional olivine; most of the mineral grains are plagioclase. The clasts show a variety of textures, including gabbroic, diabasic, and basaltic; many have been shocked and partly granulated. Some of the clasts resemble eucrites, but many appear to be more feldspathic than most eucrites. The section is notable for the complete absence of opaque minerals, except for a 1 mm metal grain. Microprobe analyses show that the plagioclase is very Ca-rich, averaging An97 (range An_95-98); pyroxene is variable in composition, Wo_1-41, En_44-79, Fs_7-47 (richer in En than most eucrite pyroxenes); several grains of olivine, Fa_11-40, were analyzed. The meteorite is a breccia, but more feldspathic than most eucrites; some of the clasts resemble the anorthositic clasts described from lunar rocks.