Northwest Africa 7989 (NWA 7989)

(Northwest Africa)

Purchased: 2013 Jul

Classification: HED achondrite (Eucrite, polymict)

History: Purchased in July 2013 by Mendy Ouzillou from a dealer in Morocco.

Physical characteristics: The stone (510 g) lacks fusion crust and has a weathered, brownish exterior; the interior consists of separated white and brownish clasts in a dark matrix.

Petrography: (A. Irving and S. Kuehner, UWS) Fragmental breccia composed predominantly of gabbroic eucrite clasts with some diabasic eucrite clasts in a sparse matrix of related debris. The grain size of pyroxene and plagioclase in gabbroic clasts ranges up to 1.4 mm. Primary minerals are exsolved pigeonite (with variable red-brown staining), calcic plagioclase (polycrystalline, birefringent), silica polymorph, ilmenite, Ti-bearing chromite, troilite and Ni-free iron metal; small amounts of secondary barite and calcite terrestrial weathering products are present.

Geochemistry: Orthopyroxene host (Fs_60.9-62.3Wo_2.1-2.2, FeO/MnO = 29-32), clinopyroxene exsolution lamellae (Fs_26.9-27.5Wo_43.4-42.6, FeO/MnO = 29-30), clinopyroxene host (Fs_27.4Wo_43.3, FeO/MnO = 29), orthopyroxene exsolution lamella (Fs_63.7Wo_3.4, FeO/MnO = 35).

Classification: Eucrite (polymict, gabbroic). This material is somewhat heterogeneous, but is notable for the relatively coarse grain size of eucrite clasts, the shocked plagioclase and the variable red-brown color of pyroxene.

Specimens: 21 g of material including one polished thin section at UWB. The main mass is held by M. Ouzillou.