Northwest Africa 3100

Morocco

Purchased 2003 June

Primitive achondrite

A 136 g complete stone with weathered crust was purchased in Rissani.  Description and classification (T. Bunch and J. Wittke, NAU): polygonal-granular, fine-grained (avg. size 0.155 mm; range, 0.03 to 0.7 mm), thoroughly recrystallized (two very small relict chondrules were observed in one of two thin sections).  Mineral modes (vol%): olivine, 78; orthopyroxene, 10; plagioclase, 5; troilite, 5; metal, 1; chromite, diopside and merrillite all <1; olivine is greatly enhanced and metal is depleted relative to LL6 chondrites.  Olivine, Fa_28.7 (FeO/MnO = 65.6; orthopyroxene, Fs_23.5Wo_0.8. (FeO/MnO = 48.8); plagioclase, An_34.1Or_3.1; diopside, Fs_12.8Wo₄₁; Ni-rich troilite, Ni = 4.2 wt%; metal (taenite only), Ni = 20.1 wt%; chromite, Cr/(Cr+Al) = 0.80, Mg/(Mg+Fe) = 0.21. Shock stage, S1; weathering grade, W2.  Oxygen isotopes: replicate analyses of an acid-washed whole rock sample by laser fluorination (T. Larson and F. Longstaffe, UWO) gave respectively d¹⁸O = 1.54, 1.15‰, d¹⁷O = -0.92, -1.07‰, D¹⁷O = -1.72, -1.66‰, which imply that this specimen has affinities with CR chondrites (Bunch et al., 2005).  Specimens: type specimens, 20.2 g, and two polished thin sections, NAU; main mass, MFarmer.