Northeast Africa 055 Martian Olivine Phyric Shergottite

Petrography: This meteorite from Mars has an igneous basaltic texture composed of poikilitically enclosed olivine chadacrysts within pyroxene oikocrysts which also enclose plagioclase laths. Some areas have a subophitic texture with plagioclase laths transecting and enclosing pyroxene and olivine. No evidence of exsolution found in pyroxenes. Accessory iron spinels are found enclosed by and adjacent to plagioclase. Composition is approximately 20% olivine, 47% pyroxene, 28% plagioclase (maskelynite), and 1% Fe-spinel. Shock effect is evident with all plagioclase converted to maskelynite. Accessory Fe-spinels include titanomagnetite (ulvöspinel), and aluminum-bearing titanian chromomagnetite.

Geochemistry: Olivine Fa_48.5±3.5, FeO/MnO=52.1±2, n=10; Low-Ca Pyroxene Fs_26.4±2.3 Wo_4.3±1.8, FeO/MnO=33±10, n=8; Pigeonite Fs_28.0±3.7 Wo_7.0±3.0, FeO/MnO=29±1, n=11; Augite Fs_23.3±0.2 Wo_27.7±0.7, FeO/MnO=25±1, n=2; Maskelynite An_48.1±1.5 Ab_49.6±1.4, n=12.