Northwest Africa 6166 (NWA 6166)

(Northwest Africa)

Purchased: 2005

Classification: Iron meteorite (ungrouped)

History: A single iron mass was purchased in Erfoud, Morocco, in 2005 by F. Kuntz (Besançon, France).

Physical characteristics: The 144 g mass measures 5 × 5 × 1.5 cm and is lens-shaped. The surface of the meteorite is covered by terrestrial iron oxidation products and lacks fusion crust .

Petrography: (M. D’Orazio, M. Gemelli, DST-PI) Etched sections show a microscopic Widmanstätten pattern given by pointed kamacite spindles 30-70 µm wide. Swathing kamacite, nucleated around primary euhedral crystals of schreibersite (100-250 µm in maximum length), is also widespread. The matrix surrounding the kamacite occurs in two different types: some zones have an homogeneous (up to 0.1 mm scale) Ni-rich metal matrix; other zones are made of a rather coarse (10-50 µm) intergrowth of Ni-rich and Ni-poor metal arranged into irregular but continuous ribbons . The heat-altered rim is partially preserved and contains some melted schreibersite crystals showing dendritic structures.

Geochemistry: Composition of the metal (ICP-MS; D’Orazio and Folco, 2003) is: Co = 0.597, Ni = 17.8 (both in wt %), Cu = 499, Ga = 4.4, Ge = < 1, As = 34.5, W = 0.02, Re = < 0.01 , Ir = 0.02, Pt = 0.04, Au = 1.51 (all in ppm).

Classification: Iron meteorite, structurally anomalous plessitic octahedrite, ungrouped, very low weathering grade.

Specimens: One 14.51 g etched full slice and one 6.92 etched endcut are on deposit at DST-PI.  Kuntz holds the main mass.