Winonaites

Northwest Africa 2627

Northwest Africa
Found 2004
Achondrite (winonaite, anomalous)

A 68 g mostly crusted, partial stone was purchased in Erfoud in October 2004. Description and classification (T. Bunch and J. Wittke, NAU): recrystallized into polygonal and subhedral grains with the exception of large orthopyroxene grains (up to 3 mm) that poikilitically enclose olivine; heavily fractured, variable grain size, and heterogeneous distribution of phases. Modal analyses (vol. %): orthopyroxene, 44; olivine, 41; FeS, 6; metal (and Fe-oxides), 5; plagioclase, 3 and minor merrillite, Ca-pyroxene and chromite. All silicates have very homogeneous compositions; olivine, Fa_13.1 (FeO/MnO = 26 g/g); orthopyroxene, Fs_12.2Wo_2.7 (FeO/MnO = 13.9 g/g); plagioclase, An_21.9; metal, Ni = 6.7 wt. % Ni. Oxygen isotope analyses are consistent with winonaites, mineralogy and mineral compositions are more consistent with lodranite assemblages. Weathering grade is W2/3 with ferric Fe staining; shock level is S2. Specimens: type example, 13.7 g, NAU: main mass, Strope/Farmer.