Northwest Africa 6203 (NWA 6203)        ~30°31’N, ~4°18’W

Bechar, Algeria

Found: 2007

Classification: Iron meteorite (IAB-MG)

History: Fourteen individual masses with a combined weight of 35.4 kg were reportedly found by Moroccan nomads along the Ziz River on the Algerian side of the Morocco-Algeria border area in 2007 and 2008. Three masses totaling 5.3 kg were acquired by Svend Buhl of Hamburg, Germany, from Mr. Abdellah Afiniss.

Physical characteristics: Individual masses show moderately eroded regmaglypts on the metal surfaces while the silicate portions appear to be more strongly eroded. Metal surfaces protected in situ from corrosion by sand abrasion have developed a chestnut colored desert patina. Sand-polished metal surfaces show a matte-finished slightly olive luster with apparent lamellae boundaries. The boundaries of metal and silicate portions are exaggerated by weathering.

Petrography: (C. Herd and G. Nadeau, UAb) The meteorite contains abundant silicate inclusions. The metal consists of coarse-grained (~5 mm width) equigranular kamacite grains with 120° grain boundaries. Neumann lines are visible within individual kamacite grains. Small (sub-mm) schreibersite grains are present within some kamacite grains and at grain boundaries. Silicate inclusions consist of irregular, mm- to cm-scale masses of fine-grained (<0.2 mm) material intergrown with kamacite. Terrestrial oxides decorate grain boundaries and fractures that penetrate well within the meteorite interior.

Geochemistry: Mineral compositions (all mol%): Silicate inclusions consist of homogeneous olivine (Fa_4.9±0.2), low-Ca pyroxene (Fs_6.9±0.3Wo_1.8±0.3), clinopyroxene (Fs_3.0±0.1Wo_44±1), and plagioclase (An_15.7±0.1Ab_81.2±0.1). Also associated with the silicate inclusions are abundant troilite, kamacite, schreibersite and graphite, the latter either fine-grained massive or cliftonitic (as intergrowths with troilite). Modal abundances in the one silicate inclusion studied in detail are approximately 30% olivine, 15% low-Ca pyroxene, 15% Ca pyroxene, 15% graphite, 10% troilite, 10% iron oxides (terrestrial), 3% kamacite, 2% plagioclase and trace schreibersite. Bulk Composition (metal): INAA data (J. Duke, UAb): Ni = 6.28 ± 0.04 wt%, Co = 0.441 ± 0.003 wt%, Ga = 81.2 ± 0.6 μg/g, Ge = 377 ± 34 μg/g, Ir = 3.55 ± 0.04 μg/g, Au = 1.51 ± 0.02 μg/g, As = 11.0 ± 0.2 μg/g, W = 0.72 ± 0.13 μg/g, Re = 0.33 ± 0.04 μg/g (uncertainties 1σ, 68% confidence level).

Classification: Iron meteorite, IAB main group, low shock, moderate weathering. Silicate inclusion mineralogy is consistent with IAB-MG. The lack of Widmanstätten pattern precludes structural classification.

Specimens: 27.6 g slice, 20.7 g of fragments, and a 149.6 g polished end-cut are on deposit at UAb; main masses 3449 g, 1873 g, SBuhl.