Northwest Africa 2373

Northwest Africa

Purchased 2004 August

Martian (olivine-phyric shergottite)

Several small stones that weigh 18.1 g were purchased in Erfoud Morocco. They are yellow brown with desert ablation/varnish surface only, no fusion crust. Description and classification (T. Bunch and J. Wittke, NAU): olivine phenocrysts (<1.25 mm in longest dimension) set in a fine-grained groundmass (<0.1 mm) of pigeonite, maskelynite, chromite, Ti-magnetite, augite, chlorapatite and sulfide.  Olivine has cores of Fa_30.7 (FeO/MnO = 51.9), rims of Fa_50.3 (FeO/MnO = 53.3) and contain micron to submicron inclusions of chromite, glass, and barite. One large olivine grain, which may be a xenocryst, is different from the rest with a core of Fa_29.1 (FeO/MnO = 43) and more abundant tiny inclusions. The wide (0.2 to 0.4 mm), inclusion-free mantle on this grain is Fa_32.3 (FeO/MnO = 39.2). Pigeonite is zoned from Fs_29.4Wo_8.4 to Fs_36.4 Wo_14.1 (FeO/MnO = 28); augite is Fs_21.8 Wo_29.1. Maskelynite is slightly zoned with a compositional average of An_52.1Or_2.1. Chromite, cr# = 87, fe# = 90.4. Overall texture, mineral content and mineral compositions strongly suggest that this stone is paired with NWA 1068.  The specimen is lightly weathered and moderately shocked. Specimens: type specimen, 3.7 g and one thin section, NAU; main mass, Birdsell.