Northwest Africa 10558 (NWA 10558)

(Northwest Africa)

Purchased: 2015 Jun

Classification: Martian meteorite (Shergottite)

History: Purchased by Stefan Ralew in June 2015 from a Moroccan dealer at the Ensisheim Show.

Petrography: (A. Irving and S. Kuehner, UWS) Diabasic texture with some preferred orientation of inequidimensional pyroxene and maskelynite grains. Composed of prismatic grains of zoned clinopyroxene (up to 4 × 0.6 mm in size) plus subordinate, smaller laths of maskelynite together with accessory ilmenite, ulvöspinel, merrillite (some with chlorapatite rims) and pyrrhotite. Rare inclusions of silica polymorph are present in pyroxene.

Geochemistry: Low-Ca pyroxene (Fs _30.9-41.6Wo_11.5-8.8, FeO/MnO = 28-35, N = 4), high-Ca pyroxene (Fs_22.2-36.4Wo_33.8-35.7, FeO/MnO = 28-32, N = 4), maskelynite (An_52.1-52.4Or_1.3-1.2, N = 2). The compositional ranges for pyroxene are more limited than in most other shergottites. Hf and Nd isotopes (M. Righter and T. Lapen, UHou): analysis of clean whole rock cutting dust gave ε¹⁷⁶Hf = -19.49 and ε¹⁴³Nd = -9.04, indicating that this specimen has affinities to enriched shergottites (like Shergotty).

Classification: Martian (diabasic shergottite, enriched).

Specimens: 2.86 g including one polished thin section at UWB; main mass with Ralew.