Northwest Africa 7657 (NWA 7657)
Purchased: Nov 2012
History: Purchased by Adam Bates from a Moroccan meteorite dealer, November 2012.
Physical characteristics: Two stones, irregular dark brown exterior with some metal and silicate visible in desert patina. Saw cut reveals ~50% bright metal patches in a light brown-gray silicate matrix, also a ~20 mm dark silicate clast containing fine-grained metal.
Petrography: (C. Agee, UNM) Microprobe examination of a polished mount shows approximately 50% silicates and 50% metal. Silicates dominated by pyroxene, but also ~25% anorthitic plagioclase, accessory silica, olivine, chromite, phosphate and troilite. Pyroxene shows lamellar exsolution, some plagioclase grains show euhedral forms, large pyroxene clast is riddled with fine metal veins and blebs. Metal is approximately 90% kamacite and 10% taenite, minor amounts of schreibersite detected.
Geochemistry: (C. Agee and M. Spilde, UNM) EMPA. Low Ca-pyroxene Fs27.9±3.1Wo3.2±0.6, Fe/Mn=27±2, n=17; high Ca-pyroxene Fs15.8±0.8Wo40.8±0.3, Fe/Mn=19±1, n=4; olivine Fa25.3±2.7, Fe/Mn=38±4, n=8, plagioclase Or0.3±0.0Ab8.6±0.6An91.1±0.6, n=6; kamacite Fe=93.03±0.46, Ni=6.49±0.25, Co=0.45±0.02 wt%, n=16; taenite Fe=60.89±1.83, Ni=38.60±1.75, Co=0.09±0.03 wt%, n=6.
Specimens: 48.1 g including a probe mount on deposit at UNM, Adam Bates holds the main mass.