Northwest Africa 2268

Northwest Africa

Found 2002 September

Achondrite (polymict eucrite)

The meteorite found by Nomads near Tindouf (South West of Algeria) weighs 65 grams and exhibits a fine fusion crust. Mineralogy and classification (A. Seddiki, UO/UJM, B. Moine, J.Y. Cottin, UJM ; V. Sautter, J.P. Lorand, M. Denise, MNHNP): This fine to medium-grained breccia contains mineral fragments of plagioclases (An85-94), pyroxenes (En84-39Wo1-8), spinel (24-51% Cr2O3), olivine (Fa71) and  silica. The rock also contains some basaltic fragments with ophitic, sub-ophitic or cumulative textures, formed by plagioclases (An86 to An91) and pigeonite (En50-33Wo10-20) and certain grains of pigeonite with augite exsolution lamellae (En28-30Wo33-40). Rare impact generated rocks are observed with mineral phenocrysts in a groundmass composed of glass. Grains of pyroxferroite are present and are locally destabilised and product an association of hedenbergite (En3-14Wo39-40), fayalite (Fa87-93) and silica. Diogenitic fragments are low in abundance (<10%) and are represented essentially by crystals of orthopyroxene. The analyses of the glass fusion crust corresponds to the bulk composition of eucrites and is characterized by high Al2O3 and CaO, and low MgO compared with howardites. The Δ17O (-0.4) of this meteorite is slightly different to HED group; 18O=4.7 and  17O=2.0. Specimens : type specimen, 20.8 g, MNHNP , thin sections, UJM, main mass, finders.