Northwest Africa 7203 (NWA 7203)

(Northwest Africa), Morocco

Purchased: 2011

Classification: Angrite

History: One stone covered by fusion crust was purchased by Luc Labenne in Tucson, Ariz., in 2011.

Petrography: (T. Mikouchi, UTok). The thin section shows a very fine- to medium-grained variolitic texture mainly composed of Ca-rich olivine and anorthitic plagioclase associated with intersitial Al-Ti-rich clinopyroxene. The largest grain size reaches to 1 mm, but it drastically becomes fine-grained showing feather-like intergrowth (<10 μm). Minor phases include ülvospinel and troilite. The presence of thin melt veins (~100 μm wide) suggests moderate shock. The variolitic texture suggests rapid cooling of magma, which is common for "quenched" angrites.

Geochemistry: (T. Mikouchi, UTok). Both olivine and Al-Ti-rich clinopyroxene are extensively zoned up to mg# <0.01. The most magnesian olivine is Fo₅₇, but contains ~1 wt% CaO. Kirschsteinite olivine (up to 20 wt% CaO) coexists with fayalitic olivine, and they show a complex intergrowth texture. The most magnesian Al-Ti-rich pyroxene has mg#=0.5. Al-Ti-rich clinopyroxene has Al₂O₃=6-10 wt% and TiO₂=2-4 wt%. Plagioclase is essentially Na-free and pure anorthite (An>99.5).

Classification: Quenched angrite most similar to NWA 1296, but the texture is different, ruling out the pairing.