Northwest Africa 6112 (NWA 6112)

(Northwest Africa)

Purchased: 2000

Classification: Ungrouped achondrite

Physical characteristics: A 1040 g stone, partially covered by fusion crust.

Petrography: The section shows a granular texture composed of elongate to rounded olivine grains (0.3-0.5 mm, ~90 vol%) and minor anhedral plagioclase (~0.2-0.5 mm) and augite (~1-2 mm). Large augite grains (~1-2 mm) poikilitically enclose rounded olivine grains. Fine-grained (partly-weathered) FeNi-FeS and orthopyroxene occur along grain boundaries of the silicate minerals.

Geochemistry: Olivine (Fa_25-28, FeO/MnO~53), Pyroxenes: Augite (n = 12), Fs_10.9±0.3En_46.2±0.3Wo_42.9±0.4 (Fs_10.2-11.2En_45.8-46.4Wo_42.1-43.6) and Low-Ca pyroxene, Fs_22.6En_76.6Wo_0.8 (n = 2), and plagioclase (Or_2-3An_20-21).

Classification: The coarse-grained granular texture indicates that this meteorite is not a chondritic meteorite, but an achondrite or primitive achondrite. The composition of olivine (Fa_25-29) is similar to L chondrites. However, the scarcity of orthopyroxene indicates that this meteorite is not related to ordinary chondrites. The mode of olivine (~90 vol%) and the presence of minor augite indicate that this meteorite is petrologically similar to brachinite group. However, the Fa composition of olivine is slightly outside the range of brachinite group (Fa_30-35) and similar to those of an ungrouped achondrite, Divnoe (Fa_20-28). On the basis of the petrologic data presented above, this meteorite is classified as an ungrouped achondrite.

Specimens: 38 g type specimen at NIPR.