Northwest Africa 7831 (NWA 7831) 27.307°N, 12.083°W
Saguia el Hamra, Western Sahara
Found: 2013 Mar
Classification: HED achondrite (Diogenite)
History: Found buried in the ground near Chouichiyat on March 3, 2013, and excavated by a team of local people.
Physical characteristics: A single large mass (at least 20 kg) composed of yellow-green crystalline material with pale orange weathering products along numerous fractures. Much of the material disintegrated into fragments upon excavation.
Petrography: (A. Irving and S. Kuehner, UWS) The specimen is composed almost entirely of translucent, yellow-green orthopyroxene with very sparse, tiny included grains of Ni-free metal, troilite, chromite, anorthite, silica polymorph and clinopyroxene. Secondary pale orange, clay-like deposits from terrestrial weathering are present along thin fractures.
Geochemistry: Orthopyroxene (Fs28.1-28.3Wo3.0-3.3; FeO/MnO = 29-31), clinopyroxene (Fs10.9Wo43.1, FeO/MnO = 26). Oxygen isotopes (K. Ziegler, UNM): analyses of acid-washed orthopyroxene by laser fluorination gave, respectively, δ17O = 1.677, 1.793, 1.810; δ18O = 3.680, 3.879, 3.875; Δ17O = -0.266, -0.255, -0.236 per mil.
Specimens: 44.5 g of material is on deposit at UWB. The remainder is held by several anonymous collectors.