Northwest Africa 6023 (NWA 6023)

(Northwest Africa)

Purchased: 2009

Classification: Brachinite-an

History: The meteorite was bought from a local meteorite dealer in Erfoud, Morocco.

Physical characteristics: Dark brownish rock with patches of fusion crust.

Petrography: A polished surface of the meteorite shows sub-mm sized shiny crystals. It displays an equilibrium texture of 200-300 μm sized olivine (about 90 vol.%), some Ca-pyroxene and chromite typically showing triple junctions between adjoining crystals. Nearly all olivine crystals are surrounded by fine-grained intergrowths of low-Ca pyroxene and metallic Fe. Strikingly, olivine shows pronounced reduced rims and the meteorite contains flaky graphite. No plagioclase has been detected.

Geochemistry: olivine: Fa_32.3±0.7 (Fa_30.4-32.9, n=14, CaO=0.11±0.02, Cr₂O₃=0.03±0.01, FeO/MnO=70±5); reduced rims in olivine: Fa_12.6-16.2; Ca-pyroxene: Fs_11.4±0.2Wo_43.3±0.3 (Fs_11.1-11.8Wo_42.6-43.8, n=13, FeO/MnO=35±3); Oxygen isotopes (K. Ziegler, UNM): material analyzed by laser fluorination gave: δ¹⁸O=5.162, 5.226, 4.838, 5.110; δ¹⁷O=2.445, 2.491, 2.269, 2.402; Δ¹⁷O= -0.281, -0.268, -0.285, -0.296 (all per mil)

Classification: Brachinite-anomalous. Mineral chemistry, high abundance of olivine, equilibrium texture and oxygen isotopes are consistent with classification as brachinite, but reduced rims and high graphite-content are typical of ureilites.