Northwest Africa 16636 (NWA 16636)

(Northwest Africa)

Purchased: 2 Feb 2019

Classification: Ordinary chondrite (L6)

History: Richard (Dick) Pugh purchased a single 58.8 g whole stone from Sidi Mohamed Ismaily on February 2, 2019 at the Tucson Gem and Mineral Show in Tucson Arizona. Mr. Ismaily told Mr. Pugh that this was an unclassified northwest African Stone. Mr. Pugh donated the entire stone to Cascadia on February 7, 2019.

Physical characteristics: Physical Characteristics: The exterior of the stone is covered by a mixture of dark brown desert varnish and black patches of remnant fusion crust. The cut face is mainly light- to medium-brown-gray, grading to orange-brown near the exterior and along three cracks. Metal and sulfide grains are visible in the cut face, which is crossed by a dark gray vein complex

Petrography: (M. Hutson, V. Mugica, and A. Ruzicka, Cascadia): In thin section, most chondrules are poorly delineated in transmitted light and are well integrated with a coarse granular matrix. The thin section is cut by a vein which is substantially opaque in transmitted light, but which shows abundant visible grains of blue-green wadsleyite. BSE images show that the vein is texturally complex; one part of the vein has a sulfide-rich core surrounded on either side by a metal-sulfide-poor zone containing wadsleyite and an equant phase that is possibly majorite, and which grades into a zone filled with rounded metal-sulfide blebs near the edge of the vein. Plagioclase feldspar grains near the vein are isotropic; many grains exceed 50 μm across.

Geochemistry: Olivine and pyroxene grains are equilibrated. Olivine: Fa_25.9±0.5, N=22; low-Ca pyroxene: Fs_22.0±0.4Wo_1.5±0.2, N=13.

Classification: Ordinary chondrite (L6) based on mineral chemistry and texture.

Specimens: Cascadia holds 50.8 g in one piece, as well as a polished thin section and material in an epoxy butt.