Northwest Africa 5804 (NWA 5804)

(Northwest Africa)

Purchased: Oct 2005

Classification: Iron meteorite (IAB, ungrouped)

History: A single specimen was purchased in October 2005 at the Munich Mineral Fair, Germany, by Andreas Gren from a Moroccan dealer.

Physical characteristics: The 726 g mass has a rounded elongated shape, with a reddish brown exterior.

Petrography: (C. Herd, UAb) Two 2.5 × 5 cm polished and etched slabs reveal an unusual microstructure consisting of cm-sized domains composed of 200 μm scale equigranular kamacite, taenite, and schreibersite grains. Graphite is present as <5 μm grains, 200 μm rounded blebs, and as mm-scale globular aggregates. Centimeter-scale domains are evident in hand specimen, which are consistent with heterogeneous distribution of kamacite, taenite, schreibersite, and graphite.

Geochemistry: INAA data (J. Duke, UAb): Ni = 11.54±0.03 wt%, Co = 0.509±0.003 wt%, Ga = 35.8±0.4 μg/g, Ge = 28±4 μg/g, Ir = 0.196±0.008 μg/g, Au = 1.04±0.02 μg/g, As = 13.0±0.2 μg/g, Cu = 307±23 μg/g, Cr = 32±5 μg/g (uncertainties 1 σ), W < 0.27 μg/g, Re < 0.05 μg/g. Although Ni, Ga and Ge concentrations are similar to the IAB-sLM/sLH group, the Au concentration is well below the minimum 1.3 μg/g required for the IAB-MG complex.

Classification: Iron meteorite, IAB-ungrouped, low shock, low weathering.

Specimens: 15.0 g and 13.7 g slabs and a 3.2 g analyzed sample (including polished mount) at UAb. Main mass with Gren.