Northwest Africa 6163 (NWA 6163)

(Northwest Africa)

Purchased: Oct 2008

Classification: Iron meteorite (ungrouped)

History: A single iron mass was purchased from a Moroccan dealer in October, 2008, by M. Graul (Bernau, Germany).

Physical characteristics: The 358 g mass, measuring 70 × 57 × 35 mm, has a cone-like shape with a surface roughly flat and one more convex. The surface is partially (>50%) covered by a brown fusion crust and presents several roughly circular depressions up to 1 cm in diameter.

Petrography: (M. D’Orazio, DST-PI) Etched sections show a well-preserved heat-affected rim and a peculiar internal structure of sub-equant, 5 to 10 mm kamacite grains with prominent Neumann bands between which are comb-net plessite bodies. Troilite occurs within kamacite as 1 to 6 mm rounded inclusions showing lamellar twinning, whereas schreibersite forms 100 to 500 µm subhedral, elongated crystals often grown at the troilite-kamacite interface. Several inclusions of troilite show, towards their contact with the host kamacite, replacements by chalcopyrite. Many small hollow spaces (from 0.5 to 10 mm in length), sometimes lined with black iron hydroxides, characterize the internal structure of this meteorite. Close to the external surface these cavities are filled with rounded, sand-sized, grains of quartz from the desert soil.

Geochemistry: Composition of the metal (ICP-MS; D’Orazio and Folco, 2003) is Co = 0.427, Ni = 8.43 (both in wt%), Cu = 258, Ga = 15.1, Ge = 54.3, As = 11.1, W = 1.55, Re = 0.48, Ir = 4.2, Pt = 9.6, Au = 1.08 (all in ppm). Reference.: D’Orazio, M. and Folco, L. (2003). Chemical analysis of iron meteorites by inductively coupled plasma - mass spectrometry. Geostandards Newsletter 27, 3, 215-225.

Classification: Iron meteorite, ungrouped, with anomalous structure.

Specimens: a 27.7 etched endcut and a 11.8 g etched full slice are on deposit at DST-PI. M. Graul holds the main mass.