Northwest Africa 6817 (NWA 6817)

Western Sahara

Found: 2011

Classification: HED achondrite (Howardite)

History: Found in Western Sahara in 2011, purchased by Jay Piatek and A. Habibi in Erfoud, Morocco, April 2011.

Physical characteristics: Total mass 1131 g. Partially covered with smooth fusion crust. Full-slice reveals many centimeter- to submillimeter-sized light-colored clasts and numerous dark clasts (<1 to 3 mm) set in a light blue-gray, fine-grained matrix. One thin dark melt vein.

Petrography: (C. Agee, UNM) Microprobe examination shows two populations of low-Ca pyroxene: ~75% eucritic and ~25% diogenitic. Augite present as exsolution lamellae primarily in eucritic pyroxenes. Total pyroxene volume ~50%, plagioclase feldspar ~40%. Silica phase, ilmenite, chromite, and troilite present. Olivine and Fe,Ni-metal absent. Larger clasts often coarse grained poikilitc pyroxene and plagioclase, some large clasts are poikilitc plagioclase, silica, pyroxene, and troilite, other clasts are very fine grained mosaics of pyroxene and plagioclase.

Geochemistry: (C. Agee and M. Spilde, UNM) Two distinct low-Ca pyroxene populations: Fs_60.0±4.0Wo_{2.3 ±0.7} Fe/Mn=31±1, N=14 (eucritic), Fs_29.1±6.2Wo_3.0±1.9 Fe/Mn=31±2, N=7 (diogenitic), augite: Fs_26.0±1.7Wo_43.7±0.7 Fe/Mn=31±1, N=11, plagioclase Or_0.6±0.1Ab_10.8±0.6An_88.7±0.7.

Classification: Achondrite (howardite): light surface weathering, fresh cut surface has minimal weathering, moderate shock grade.

Specimens: 50 g on deposit at UNM, J. Piatek and AHabibi each hold approximately half of the main mass.