Northwest Africa 4051

Kem Kem Basin, Algeria

Find: April 2004

Achondrite (eucrite)

History: A stone with brownish-black fusion crust was purchased by a member of Moussa Minerals & Fossils, England, in 2004 from a Moroccan dealer.

Physical characteristics: The 828 g meteorite is almost entirely covered in a fusion crust. Terrestrial weathering is present in terms of charred fusion crust and calcite veins occurring throughout the rock.

Petrography: (M. Anand, NHM and OU) The rock consists of large mineral (up to 3 mm) and lithic clasts (up to 6 mm). Pyroxene and plagioclase grains dominate (usually about 100–500 µm), in a highly immature matrix of the same texture and mineral composition but smaller grain size (<100 µm). Plagioclase occurs as subangular to lath-shaped crystals. Minor phases include chromite, ilmenite, silica, iron sulfide, and Fe,Ni-rich metal.

Mineral compositions and geochemistry: EMP analysis, conducted at the NHM, of mineral phases: pigeonite (En₅₀Wo_5.2–En₃₈Wo_17.5), which is the dominant pyroxene phase containing exsolution lamellae of orthopyroxene (En₄₇Wo_2.3–En₄₁Wo₅) and in some cases of subcalcic augite = En₃₅Wo₂₆–En₃₅Wo_20.5. The Fe/Mn ratio in pyroxenes varies from 27 to 38. The anorthite content of plagioclase varies from An₈₅ to An₉₃. Chromite grains contain Al₂O₃ = 7–14 and TiO₂ = 2–5.6 (both wt%). Ilmenite contains MgO = 0.6–1.3 and MnO = 0.8–1 (both wt%). Oxygen isotopes: (R. C. Greenwood and I. A. Franchi, OU) δ¹⁷O = 1.861, δ ¹⁸O = 3.994, Δ¹⁷O = −0.216 (all as ‰).

Classification: Achondrite (brecciated basaltic eucrite).

Type specimen: A total of 20 g is on deposit at the NHM. Moussa holds the main mass.