Northwest Africa 6234 (NWA 6234)

Mali

Found: 2009

Classification: Shergottite

History: A pale-colored stone found in Mali in 2009 was purchased in February 2010 by an anonymous collector.

Physical characteristics: A fine-grained, partly fusion-crusted stone (55.7 g) displaying fluted abrasion features on several sides. The fresh interior is pale gray with evenly-distributed, larger, pale-tan grains, and is crosscut by several thin, black shock veins.

Petrography: (A. Irving and S. Kuehner, UWS): Porphyritic texture, with small (0.15 to 0.35 mm) olivine phenocrysts in a finer grained groundmass composed mainly of prismatically zoned pigeonite (with rare subcalcic augite) and maskelynite with accessory ferroan olivine, chromite, titanomagnetite, ilmenite, merrillite and pyrrhotite.

Geochemistry: Olivine phenocrysts (core Fa_26.1-26.5, rim Fa_39.2; FeO/MnO = 47.1-56.6), pigeonite (Fs_28.5-38.7Wo_5.9-16.3, FeO/MnO = 30.3-38.3), augite (Fs_23.3Wo_35.4, FeO/MnO = 30.7), groundmass olivine (Fa_47.3, FeO/MnO = 55.0), plagioclase (An_52.3-55.1Or_1.8-2.2). Bulk composition (M. Gellissen, XRF, Koln; C. Herd, ICPMS, UAb): powder prepared from clean cutting dust gave the following elemental abundances (in wt%): SiO₂ 44.7, FeO 22.6, MgO 16.3, CaO 6.4; (in ppm) La 1.3, Ce 3.1, Nd 2.0, Sm 1.1, Yb 1.2, Lu 0.17, Ni 540.

Classification: Achondrite (Martian, olivine-phyric shergottite). This specimen has essentially the same external appearance, grainsize, texture and mineral compositions as NWA 2990 and NWA 5960, and evidently is paired with those stones.

Specimens: A total of 20.0 g of type material and one polished thin section are on deposit at UWS. The remaining material is held by an anonymous collector.