Northwest Africa 2968

Northwest Africa

Find: 2004

Achondrite (ungrouped)

History and physical characteristics: A bag of rectangular to blocky, dark brown meteorite fragments, with a total mass of 268 g and collected by nomads in 2004, was purchased in Erfoud, Morocco, in November 2005.

Petrography: (T. Bunch and J. Wittke, NAU; A. Irving, UWS) A massive olivine-rich rock of very large grain size (17 to >25 mm; maximum size is unknown because of the tendency to fracture on cutting). Curved to linear compression and shear fractures are subparallel to one of the extinction directions in olivine and are responsible for the common rectangular/blocky habit. Twenty-three pieces (1.8 to 20.1 g) were surveyed. Olivine accounts for >95 vol% with small amounts of tiny grains (<0.03 mm) of orthopyroxene, metal, troilite, and pyrrhotite commonly found within fractures and as rare inclusions in olivine. Large domain offset, isolated mosaicism, and undulatory extinction are prevalent in olivine.

Mineral compositions and geochemistry: Equilibrated olivine (Fa_7.5±0.2; FeO/MnO = 48; Cr₂O₃ and NiO < 0.03 wt%), orthopyroxene (Fs_6.7Wo_1.5; FeO/MnO = 26), kamacite (Ni = 4.7–6.8 wt%), taenite (Ni = 39.1–50.7 wt%), troilite (Ni = 0.36 wt%), pyrrhotite (Ni = 1.7–4.7 wt%). Oxygen isotopes: (D. Rumble, CIW) Analysis of two cleaned and metal-free samples by laser fluorination yielded δ¹⁷O = 1.44, 1.46; δ¹⁸O = 3.08, 3.64 and Δ¹⁷O = −0.178, −0.212 (all ‰).

Classification: Achondrite (ungrouped).

Type specimen: A 22 g sample is on deposit at NAU. Reed holds the main mass.