Northwest Africa 7531 (NWA 7531)

Morocco

Found: 2009

Classification: Carbonaceous chondrite (CR7 polymict breccia)

History: An anonymous buyer purchased an 868 g stone in Erfoud, Morocco in 2009.

Physical characteristics: The fresh stone has a smooth, dark ablation crust with a coarse network of shrinkage cracks.

Petrography: The interior consists of angular clasts of two lithologies. The dominant lithology comprises ~66 vol%, and is green, consisting of crushed, recrystallized coarse-grained olivine, orthopyroxene poikiloblasts (olivine chadacrysts), plagioclase, minor chromite, taenite, FeS, and Cl-apatite. Modal analyses (vol %): Orthopyroxene, 42; olivine, 37; plagioclase, 14; other, 7. The second lithology is gray, recrystallized, lacking chondrules, with coarse-grained orthopyroxene poikiloblasts (olivine chadacrysts), smaller grained olivine, minor augite, recrystallized troilite with tiny silicate entrainments, metal, merrillite, and chromite. Boundaries between clasts are occupied with a 0.5 to 1.0 mm thick layer of finely granulated, recrystallized "rock flour".

Geochemistry: The green lithology has olivine, Fa_30.8, FeO/MnO = 90; orthopyroxene, Fs_27.4Wo_4.2, FeO/MnO = 44; plagioclase An_14.7Or _5.4; chromite cr# = 90, taenite Ni = 42 wt %. The LL lithology contains olivine Fa_28.6, FeO/MnO = 58; orthopyroxene, Fs_24.2Wo_2.0. Oxygen isotopes (D. Rumble, CIW): Replicate analyses of acid-washed material by laser fluorination gave, respectively for the greenish lithology Δ¹⁷O = -0.988 and -0.978; δ¹⁷O = 2.899 and 2.729; δ¹⁸O = 7.391 and 7.048. LL lithology Δ¹⁷O = 1.193 and 1.194; δ¹⁷O = 3.903 and 3.851; δ¹⁸O = 5.152 and 5.052 (all per mil). Compositional, petrographic and oxygen isotopic data for the green lithology are consistent with CR7, and LL7 for the gray lithology.

Classification: CR7 polymict breccia with an LL7 clast.

Specimens: A total of 22 g is at UWB; main mass holder is anonymous.