Northwest Africa 10170 (NWA 10170)

(Northwest Africa)

Purchased: Jan 2015

Classification: Martian meteorite (Shergottite)

History: The sample was discovered near the Moroccan-Algerian frontier and purchased at the Tucson salon from an anonymous Moroccan dealer.

Physical characteristics: Three crusted stones with a general similarity to NWA 2990 when cut. The type specimen includes pieces of all three stones.

Petrography: (R. Hewins, S. Pont, B. Zanda, MNHNP) Olivine occurs as euhedral to subhedral microphenocrysts and zoned phenocrysts, 100 μm to 1.5 mm in size. They contain melt and pyroxene inclusions. Olivine is set in a mesostasis of prismatic to subophitic pyroxene and feldspar, with a texture similar to those of NWA 2990 and NWA 6234. Chromite is the main accessory mineral. The "feldspar" is almost entirely free of fractures and is continuous like glass between the pyroxene grains. It is presumed to be maskelynite because it looks the same as glass identified as maskelynite by Raman spectroscopy in NWA 10171.

Geochemistry: Mineral compositions and Geochemistry: (R. Hewins, MNHNP) The olivine composition is Fo_67.2±7.7 (Fa_20-42), with an FeO/MnO ratio of 52.1. The pigeonite composition is En₆₉Fs₂₈Wo ₄ to En₅₂Fs₂₉Wo₁₉, with average core composition En_65.8±1.5 and the atomic Fe/Mn ratio 31.9. Spinel contains 28-54 wt% Cr₂O₃. Stoichiometric An_55-48Ab_43-50Or₂ is free of fractures and apparently glass (maskelynite). Mineral compositions resemble those of NWA 6234 (Gross et al., 2012) but the latter has more calcic plagioclase (An_65-58).

Classification: (R. Hewins and B. Zanda, MNHNP) The meteorite has SNC Fe/Mn ratios and is classified as an olivine-phyric shergottite.