Northwest Africa 480

Northwest Africa

Found 2000 November

Martian meteorite (basaltic shergottite)

A 28 g stone almost completely covered with fusion crust was found in Morocco. Classification and mineralogy (J-A. Barrat, UAng; A. Jambon, UPVI; Violaine Sautter, MNHNP; Ph. Gillet, ENSL): has a coarse-grained basaltic texture consisting predominantely of subhedral to euhedral pyroxene (up to 3 mm) and interstitial, lath-shaped maskelynite; accessory minerals include merrilite, chlorapatite, pyrrhotite, Fe-oxides, fayalite and silica; pyroxenes show complex zonation with Mg-rich pigeonite cores (Fs₂₆Wo₄), followed by augite (Fs₂₉Wo₃₀), and mantled by Fe-rich pigeonite (Fs₈₄Wo₁₁); no pyroxferroite has been detected; maskelynites are homogeneous, An_46–50Ab_52–48Or_~2; merrilite forms rounded grains (up to 100 µm) and is Fe-rich (~5 wt% FeO), commonly with 6–40 µm thick rims of fayalite (Fa_~95), silica, Fe-Ti oxides, and pyrrhotite; silica (stishovite) occurs as irregular grains in maskelynite or at grain boundaries to pyroxene and is surrounded by radiating cracks. Oxygen isotopes (M. Javoy and E. Petit, IPGP): δ₁₇O = +2.91·, δ₁₈O = +4.78·, and ∆₁₇O = +0.42·. Specimens: main mass, 25 g, CNES.