Northwest Africa 6600 (NWA 6600)

Morocco

Found: 2010

Classification: Ureilite

History: A single mass was found just south of Erfoud, Morocco, in December 2010.

Physical characteristics: Dark, coarsely granular surface. Interior shows a mosaic of green and brown olivine and pyroxene with grain sizes 1-3 mm; grain boundaries do not take a polish; some iron staining present.

Petrography: (C. Agee, UNM) Thin section shows approx. 75% olivine and 20% pigeonite, with numerous Fe-Ni-metal veins occupying grain boundaries and crosscutting silicates. Many of the veins have been oxidized. The metal veins are commonly haloed by tiny metal blebs grading into adjacent olivine crystals. The primary population of olivine and pigeonite crystals are 1-3 mm, with few inclusions, while smaller olivine grains 50-200 μm are often riddled with metal blebs and opaque intergrowths. Graphite may be present at grain boundaries. A single, small, Cr-rich sulfide was observed.

Geochemistry: (C. Agee and M. Spilde, UNM) EMPA. Olivine cores Fa_21.0±0.7, Fe/Mn = 45 ± 4, Cr₂O₃ = 0.71 ± 0.01 wt%, n=6, small olivines at grain boundaries near metal blebs and possible graphite Fa_8.7±1.2, Fe/Mn = 16 ± 2 Cr₂O₃ = 0.76 ± 0.04 wt%, n=2, pigeonite (cores and rims) Fs_{18.1 +}/- 0.2Wo_{8.6 +}/- 0.1, Fe/Mn = 27 ± 1, Cr₂O₃ = 1.15 ± 0.02 wt%, n=7, metal (wt%) Fe = 95.30 ± 0.50, Ni = 4.04 ± 0.38, Co = 0.37 ± 0.05, n=4, Cr-rich Fe-sulfide (wt%) Fe = 49.15, Cr = 9.99, S = 37.99.

Classification: achondrite (ureilite)

Specimens: Thompson holds the main mass, type specimen of 25.2 g total, 1.1 g fragment cast in epoxy for microprobe analysis, on deposit at UNM.