Northwest Africa 12726 (NWA 12726)

(Northwest Africa)

Purchased: 2010 Feb

Classification: Ordinary chondrite (LL4)

History: Purchased in Tucson by Bob Falls in February 2010. A piece was brought to Cascadia by Fred Olsen.

Physical characteristics: Sample has black, patchy remnant fusion crust and a weathering patina. Already cut faces have chondritic texture with abundant sulfide and metal and rust haloes.

Petrography: (M. Ream, M. Hutson, A. Ruzicka, Cascadia) In thin section, matrix is black and fine-grained, with well-defined chondrules. Minor clinoenstatite is present. A 2.5 mm × 2.3 mm clast is present, which is cut off on its long axis by the edge of the thin section. The clast has well-defined chondrules, matrix that is darker than the host, and contains abundant oriented troilite, including a ~0.17 mm thick vein. Pyroxenes in the clast are zoned in BSE images.

Geochemistry: Mineral compositions and geochemistry: Olivine and pyroxene grains in the host lithology are relatively equilibrated (Fa_27.9±0.3, N=14; Fs_21.6±2.8Wo_1.0±0.5, N=33). Clast olivine (Fa_28.0±0.4, N=9) is essentially identical with host olivine. Clast pyroxene (Fs_21.7±7.7Wo_1.9±1.1, N=11) has the same mean Fs content, but a much greater range of compositions than host pyroxene.

Classification: Ordinary chondrite (LL4) based on chemistry and texture.

Specimens: Cascadia holds 30.1 g in three pieces, a polished thin section, and a mounted butt. The main mass is held by Bob Falls (no address given).