Northwest Africa 2624

Northwest Africa

Purchased 2004 August

Achondrite (ureilite)

A 241 g single, mostly crusted stone, was purchased in Erfoud, Morocco. Description and classification (T. Bunch and J. Wittke, NAU): equigranular, fine-grained (< 0.8 mm) typical ureilite. Olivine is highly fractured with closely spaced, subparallel fractures normal to [001]. Fractures apparently served as channel ways for reducing (smelting) activity; grain edges have a saw tooth appearance of alternating, greater reduced rims together with deposits of carbonaceous-metal-silicate-masses (CMSM) that permeated fractures and less-reduced rims that are between fractures.  Olivine cores, Fa_19.6, rims are Fa_9.8-13.9; low-Ca pigeonite, Fs_16.8Wo_2.9-3.8; high silica glass in CMSM, SiO₂ = 78.8 wt. % and Al₂O₃ = 15.4 wt. %. Primary metal inclusions in olivine, Ni = 2.5 wt. % and Cr = 0.60 wt. %; reduction-derived metal, Ni = < 0.45 wt. %. Moderate level of reduction (R3); weathering is very low grade and the shock level is S2. Specimens: type example, 21.6 g, NAU; main mass, GHupé.