Northwest Africa 6583 (NWA 6583)

(Northwest Africa)

Purchased: 2010 Oct

Classification: Iron meteorite (ungrouped)

History: A single iron mass was purchased from a Moroccan dealer in October 2010 by M. Graul, Bernau, Germany.

Physical characteristics: The 1825 g mass, measuring 105 × 100 × 38 mm, has a flattened shape. The part embedded in soil (~40%) is covered by caliche, whereas the exposed surface is glossy-brown and presents 40-45 rounded depressions from 0.5 to 1 cm in diameter.

Petrography: (M. D’Orazio, A. Fazio, DST-PI) Etched section shows a polycrystalline texture composed of roughly equiaxal grains (0.1 to 2 cm) of ataxitic Fe-Ni. The Fe-Ni grains have a martensitic texture. Rounded, twinned and polycrystalline inclusions of troilite, rosettes and isolated crystals of graphite, and large skeletal crystals of schreibersite are common. Silicates occur as isolated euhedral crystals of enstatite and rare forsteritic olivine, and as aggregates of enstatite with overgrowths of diopside or with troilite-rich reaction rims. Many troilite grains contain inclusions of several types of Mn-Mg-Fe-Zn-Cu sulfides. Melted crystals of schreibersite and troilite showing dendritic textures are present in the external portion of the section. Terrestrial weathering is low.

Geochemistry: Composition of the metal (ICP-MS; D’Orazio and Folco, 2003) is Co=0.430, Ni=18.0 (both in wt%), Cu=1350, Ga=52, Ge=125, Ir=0.19, Au=1.13 (all in ppm). Composition of the silicates (all mol%): enstatite (En_98.2±0.3Wo_1.4±0.2), diopside (En_51.6±1.0Wo_47.8±0.6).

Classification: Iron meteorite, ungrouped, with anomalous structure, silicate inclusions and low weathering.

Specimens: A 60.5 g etched end cut is on deposit at DST-PI. MGraul holds the main mass.