Northwest Africa 12912 (NWA 12912)

(Northwest Africa)

Purchased: 12 Dec 2016

Classification: Ordinary chondrite (LL3)

History: BBaecker purchased an NWA meteorite on Ebay on December 12, 2016, and donated seven pieces to Cascadia on February 4, 2017.

Physical characteristics: Cascadia received seven small pieces that are medium- to dark-brown with patches of tan caliche on surfaces.

Petrography: (M. Hutson, A. Ruzicka, R. Kostynick, Cascadia): Distinct chondrules set in an opaque background are visible in thin section. Metal and sulfide have been replaced by iron hydroxides, and plucked, leaving holes in the poorly-polished thin section. No shock veins were visible using the optical microscope. Strong zoning of silicates is evident in BSE images. Chondrules are partly surrounded by a melt matrix. Small (?50 μm across) chromite-plagioclase patches are visible, mainly inside larger pyroxene grains. Chondrules average apparent diameter 0.89 mm (N=18).

Geochemistry: Mineral compositions and geochemistry: Olivine and pyroxene grains are highly unequilibrated: Fa_28.6±8.1, N=32; Fs_13.5±9.5Wo_1.7±1.6, N=17.

Classification: Ordinary chondrite (LL3) based on olivine fayalite content and average chondrule diameter.

Specimens: Cascadia holds 6.6 g in eight pieces, in addition to a polished thin section and a mounted butt. The main mass is held by BBaecker: Bastien Baecker, Huntsville, AL