Northwest Africa 7908 (NWA 7908)

(Northwest Africa)

Purchased: Feb 2004

Classification: HED achondrite (Diogenite)

History: A pre-cut specimen was purchased from a Moroccan trader by Edwin Thompson, and a portion was donated to Cascadia, in February, 2004.

Physical characteristics: A cut slab shows grey clasts ranging from <1 mm to 1.5 cm set in a light-brown matrix. Black clasts are also present. Rust halos surround sparse metal grains in the matrix. The surface of the sample is rough, light brown to grey to black, and mostly lacks fusion crust.

Petrography: (A. Ruzicka, Cascadia) In thin section the meteorite consists almost entirely of low-Ca pyroxene and chromite. Coarse-grained (1-2 mm) orthopyroxenite (gray) and chromite (black) clasts are set in a matrix of smaller pyroxene and chromite clasts. Grains are highly fractured and pyroxene shows undulose to mosaic extinction. One metal grain is partly replaced by weathering product.

Geochemistry: Phase compositions are highly equilibrated: low-Ca pyroxene Wo_1.6±0.1 Fs_25.1±0.8 Fe/Mn =26.5±2.7 (N=37), chromite Cr/(Cr=Al) = 0.83± 0.01 Fe/(Fe+Mg)= 0.78± 0.02 (N=14) (atomic units).

Classification: Achondrite (diogenite). Textures and mineralogy suggest a monomict orthopyroxenitic breccia. Minor weathering.

Specimens: 27.0 g, one polished thin section, and one butt are on deposit at Cascadia.  Thompson holds the main mass.