Northwest Africa 2635

Northwest Africa

Purchased October 2004

Achondrite (ungrouped)

A 4.2 kg, partially crusted stone was purchased in Erfoud, Morocco. Description and classification (T. Bunch and J. Wittke, NAU), results from one thin section (2.4 cm²): mostly recrystallized into fine-grained (<0.5 mm, avg. = 0.185 mm) polygonal and subhedral grains with the exception of several medium to large (1.2–3.0 mm) orthopyroxene grains that contain very small olivine (<0.1 mm) inclusions. Olivine and orthopyroxene analyses are homogeneous within the precision of the electron microprobe (± 0.15 mol %) and indicate H chondrite affinities. Olivine, Fa_18.9 (FeO/MnO = 38.1); orthopyroxene, Fs_16.8Wo_2.9 (FeO/MnO = 20.0); plagioclase, An_15.1Or_4.7; metal (only taenite found), Ni = 18.9 wt. %; chromite (only one grain found), cr# = 84.5; FeS, Ni = 1.42 wt. % and Co = 0.28 wt. %, minor merrillite. Most metal has been oxidized; specimen contains ~70% olivine implying it contained less metallic iron than an H chondrite when fresh. Oxygen isotope replicate analyses (D. Rumble, CIW) of acid washed, bulk sample by lased fluorination gave δ¹⁷O = 3.23 and 2.98, δ¹⁸O = 5.03 and 4.37 and Δ¹⁷O = 0.614 and 0.708. Weathering grade, W4 with staining; shock level, low. Specimens: type sample, 23.2 g, NAU; main mass, Strope/MFarmer.