Northwest Africa 2993

Algeria

Find: 2006

Achondrite (ungrouped)

History and physical characteristics: A fully crusted, complete stone of 625 g was recovered from the lower Algerian desert in June 2006 and purchased in Erfoud in August 2006 by A. Aaronson.

Petrography: (T. Bunch and J. Wittke, NAU; A. Irving, UWS) Protogranular texture with a grain size range of 0.3– 3.4 mm (mean = 1.35 mm) for silicates and 0.3–5 mm for metal (mean = 2.4 mm). Modal analyses (6.4 cm²; vol%): orthopyroxene, 37; olivine, 32; metal, 30; sulfide, 1. Several metal grains have taenite cores mantled by kamacite. Taenite grain shape is roughly similar to the outline of the entire metal grain; embryonic plessite is evident in a few taenite cores. No directional fabric was recognized. Fusion crust is lightly to moderately altered and weathering is limited to minor oxidation of kamacite with the presence of minor oxide veining.

Mineral compositions and geochemistry: Olivine (Fa_12.3±0.2; FeO/MnO=32), orthopyroxene (Fs_11.2±0.02Wo_1.2; FeO/MnO = 19), kamacite (Ni = 4.6 wt%). Oxygen isotopes: (D. Rumble, CIW) A cleaned and metal-free sample was analyzed by laser fluorination. Replicate analyses are respectively, δ¹⁷O = 1.129, 1.220; δ¹⁸O = 2.527, 2.661; Δ¹⁷O = −0.2006, −0.1802 (all ‰).

Classification: Achondrite (ungrouped). Petrography and geochemistry are consistent with lodranites; oxygen isotopes are inconsistent with lodranites/acapulcoites and are closest to the IAB irons and winonaite trend.

Type specimen: 20.3 g and one polished thin section are on deposit at NAU. The main mass holder is anonymous.