Northwest Africa 3151

Morocco or Algeria

Find: April 2005

Achondrite (brachinite)

History: A 1500 g complete stone with a thin, translucent crust was purchased by G. Hupé in Tagounite, Morocco, in April 2005.

Petrography and Geochemistry: (A. Irving and S. Kuehner, UWS) Coarse-grained dunitic rock (grain size 0.7–1.6 mm) with protogranular texture, composed predominantly of olivine (Fa_35.7; FeO/MnO = 81; 95 vol%) with minor clinopyroxene (Fs_10.5–10.6Wo_44.7–45.2; FeO/MnO = 44; Cr₂O₃ = 0.65 Al₂O₃ = 0.95 [both wt%]), altered metal (with some relict taenite), troilite, chromite (Cr/(Cr+Al) = 0.727–0.731) with very rare K-poor, sodic plagioclase (An_36.2–39.9Or_0.2), and orthopyroxene. Although the silicate minerals are fresh, terrestrial weathering has altered some of the primary metal to hydroxides, which also form thin coatings along grain boundaries. Oxygen isotopes: (D. Rumble, CIW) Replicate analyses of acid-washed whole rock samples by laser fluorination gave δ¹⁸O = +4.86 ± 0.03, δ¹⁷O = +2.42 ± 0.02, ∆¹⁷O = −0.15 ± 0.02 (all ‰).

Classification: Achondrite (brachinite).

Specimens: A 20 g type specimen and one polished thin section are on deposit at UWS. GHupé holds the main mass.