Northwest Africa 6162 (NWA 6162)

Northwest Africa

Found: 2009 Mar

Classification: Martian meteorite (Shergottite)

History: A small stone was found in March 2010 near Lbirat in southern Morocco and purchased by Stefan Ralew and Martin Altmann.

Physical characteristics: A single very fresh 89 g stone completely coated by black fusion crust with shiny, dark olivine grains visible. The interior is light gray with obvious glassy maskelynite and larger pale yellow grains of olivine, and small pockets of black shock glass.

Petrography: (A. Irving and S. Kuehner, UWS): Porphyritic texture. Larger anhedral olivine grains (some in clusters, and containing Cr-rich chromite inclusions) are set in a groundmass composed mostly of pigeonite and plagioclase (maskelynite) with accessory olivine, chromite, pyrrhotite and Mg-bearing merrillite.

Geochemistry: Olivine (core Fa_29.6-29.2, rim Fa_34.9, FeO/MnO = 48.4-54.2), pigeonite (Fs_22.9-28.6Wo_5.0-9.7, FeO/MnO = 27.5-30.4), plagioclase (An_62.1-65.8Or_0.5-0.3). Oxygen isotopes (D. Rumble, CIW): acid-washed material analyzed by laser fluorination gave, respectively δ¹⁸O = 4.68, 3.98; δ¹⁷O = 2.75, 2.36; Δ¹⁷O = 0.288, 0.271 per mil. Bulk composition (M. Gellissen, XRF, U. Cologne; C. Herd, ICPMS, UAb): powder prepared from clean cutting dust gave the following elemental abundances (in wt.%): SiO₂ 46.6, FeO 18.3, MgO 21.8, CaO 5.1; (in ppm) La 0.25, Ce 0.66, Nd 0.61, Sm 0.43, Yb 0.75, Lu 0.12, Ni 220. The rare earth element abundances indicate that this is a depleted shergottite.

Classification: Achondrite (Martian, shergottite, olivine-phyric). This specimen is not paired with other shergottites from northwest Africa, but has mineralogical similarities to Sayh al Uhaymir 005 and pairings found in Oman. This specimen shows no evidence of terrestrial weathering, and is much fresher than most other known depleted olivine-phyric shergottites.

Specimens: A total of 17.8 g of type material, one polished thin section and a polished mount are on deposit at UWS; a further 3.2 g is held by J. Jones (JSC). The remaining material is held by anonymous collectors and institutions.