Northwest Africa 8539 (NWA 8539)

(Northwest Africa)

Purchased: 2012

Classification: Iron meteorite (IAB, ungrouped)

Petrography: As previously described for NWA 8154 and NWA 8155, the metal consists of tiny grains 0.15 mm, with no evidence of an octahedral pattern. The structures are anomalous. The absence of a pattern suggest fast cooling. The small graphite ellipsoids (sometimes arranged like the petals of a flower) may reflect the locations of the last, C-rich melt to crystallize.

Geochemistry: UCLA INAA data: Co, 4.70 mg/g; Ni, 134.5 mg/g; Ga, 51.0 μg/g; Ge,~294 μg/g.; Sb 650 ng/g; As, 16.5 μg/g; Ir 27.0 μg/g; Au, 1.602 μg/g.

Classification: Based on their high contents of Au, As and Sb this meteorite (NWA 8539) and its three siblings (NWA 8154, 8155 and 7795) are classified ungrouped members of the IAB complex. However, non-IAB ungrouped irons have lower contents of these elements (and especially of Sb). It is ungrouped because it does not consistently plot in the Ni-Au, As-Au, Co-Au and Ga-Au fields of the IAB main group or of the five IAB subgroups.