Northwest Africa 12636 (NWA 12636)

Northwest Africa

Purchased: 2018

Classification: HED achondrite (Diogenite)

History: One stone weighing 967 g was found in Morocco prior to 2018. Blaine Reed purchased the sample from a meteorite dealer while at the 2018 Tucson Gem and Mineral Show.

Physical characteristics: The sample has a yellowish-brown exterior with a few small patches of black fusion crust. The sample has yellowish-orange interior that is brecciated and friable. The cut face shows angular-subrounded clasts up to 1.5cm in long dimension.

Petrography: Description and classification (A. Love, App): Sample is a breccia composed of diogenitic lithic fragments and coarser grained cataclastic clasts mixed within a comminuted host of similar materials. Lithic clasts are composed of interlocking, orthopyroxenes which share 120º grain boundaries. Orthopyroxenes contain Cpx inclusions and exsolution lamellae (up to 0.5µm) within crystals. Additional minerals are silica polymorphs, hercynitic chromite, FeS, and rare Ni-free iron metal. Orthopyroxenes within some lithic clasts exhibit normal extinction and equilibrium textures.

Geochemistry: (A. Love, App) low Ca pyroxene: Fs_27.2±0.6Wo_1.5±0.1, Fe/Mn=26.6±0.6, n=14; high Ca pyroxene Fs_10.5±0.4Wo_44.9±0.5, Fe/Mn=22.5±1.1,n=4.

Classification: Monomict diogenite breccia. Fe/Mn compositions of pyroxenes indicate this sample is diogenite meteorite. Textures and Fs compositions of pyroxenes indicate this sample is a diogenite.

Specimens: Blaine Reed holds the main mass. Two slices weighing 28.13 g and a polished mount are on deposit at App.