Northwest Africa 2046

Algeria

Purchased 2003 September

Martian meteorite (basaltic shergottite)

A 63 g complete and partially crusted stone found near Lakhbi, Algeria was purchased from a Moroccan dealer in 2003 September by MFarmer.  The ellipsoidal stone has an average width of 30 mm, with a 1 to 3 mm thick weathering rind; the interior is very fresh and unweathered.  Classification and mineralogy (J. Wittke and T. Bunch, NAU; A. Irving and S. Kuehner, UWS): olivine-orthopyroxene-phyric basaltic rock.  Subhedral to euhedral, dark brown olivine phenocrysts (up to 2.2 mm long) are strongly zoned from cores of Fa_15.7 to rims of Fa_47.9, and subhedral to euhedral, prismatic orthopyroxene phenocrysts (up to 2.1 mm long) have cores as magnesian as Fs_17.7Wo_2.5, surrounded by irregularly zoned mantles with both pigeonite and augite, and pigeonite rims as ferroan as Fs_39.0Wo_12.5.  The groundmass consists mainly of zoned pigeonite (Fs₃₀Wo_6.5 to Fs₄₀Wo₁₃) intergrown with maskelynite (zoned from cores of Ab_25.5Or_0.1 to rims of Ab_36.5Or_1.1) and small grains of relatively ferroan olivine (Fa_47.6-58.1).  Accessory minerals include Ti-chromite (Al/(Al+Cr) = 13.8-28.3), chromite, ilmenite, Cr-ulvöspinel, pyrrhotite (commonly in parallel growth with ilmenite), merrillite, rare chlorapatite, and rare fayalite (which occurs as a reaction rim on groundmass pigeonite in contact with ilmenite or pyrrhotite).  Trapped melt inclusions in olivine contain aluminous diopside, pleonaste, chromite, merrillite and glass.  Large, prismatic orthopyroxene phenocrysts exhibit preferred orientation; olivine phenocrysts are weakly oriented and tend to occur in clusters.  Textures and mineral compositions are similar to those in olivine-orthopyroxene-phyric shergottite NWA 1195, but the olivine cores in NWA 2046 are more magnesian (Irving et al., 2004).  Specimens: type specimen, 12.2 g, and one polished thin section, NAU; one polished thin section, UWS; main mass, Strope.