Northwest Africa 10516 (NWA 10516)

(Northwest Africa)

Purchased: 2002 Feb

Classification: Ordinary chondrite (L3-6)

History: Donated to Cascadia by Edwin Thompson, who obtained the meteorite in February 2002 at the Tucson Gem and Mineral Show from a Moroccan trader.

Physical characteristics: Stone with brown-red weathering patina covering both broken and curved surfaces; the latter contains remnant fusion crust. Polished cut face shows apparent breccia texture with small patches of dark, apparent shock melt and one truncated shock vein.

Petrography: (A. Ruzicka and K. Farley, Cascadia) In thin section, a breccia composed of an intimate mixture of mineral and chondrule fragments with diverse (type 3-6) characteristics and some larger clasts; areas between chondrules are mainly composed of smaller chondrule and mineral fragments, although rare fine-grained matrix is present in places. BSE imaging shows that most of the rock (“host”) is composed of type 4-6 lithologies, with equilibrated olivine, and coarse plagioclase (30-150 μm long, one grain up to 460 μm long), intermixed with well-defined chondrules and fragments, some glass-bearing. Contains a 4 mm long granoblastic-textured (type 6) chondritic lithic clast.

Geochemistry: (K. Farley and A. Ruzicka, Cascadia) Host dominated by equilibrated olivine (median Fa_24.2, N=55) and low-Ca pyroxene (median Fs_20.7, N=52) but also contains more varied olivine (Fa_5.8-32.5) and low-Ca pyroxene compositions (Fs_2.9-38.7). Overall average of mixture including both equilibrated and more varied compositions is olivine (Fa_23.4±4.9, N=55), low-Ca pyroxene (Fs_18.0±6.4Wo_1.1±1.0En_80.9±6.8, N=52), Ca-rich pyroxene (Fs_7.2±2.6Wo_42.1±4.4En_50.7±7.0, N=4), plagioclase (Ab_82.0±1.2Or_9.0±4.3An_10.9±1.6, N=7), alkali feldspar (Ab_83.1±1.2Or_42.9±2.0An_9.6±0.9, N=3).

Classification: L3-6 finely intermixed genomict breccia. Type 5-6 lithology implied by abundant equilibrated olivine and pyroxene and common coarse feldspar grain sizes; type 3 lithology implied by presence of magnesian olivine and glass in chondrules and clasts.

Specimens: Cascadia holds the entire sample, consisting of 7.0 g in two pieces, a polished thin section, and a potted butt.