Nwa 1586: Macrosmelting in a Monomict Ureilite

Introduction: NWA 1586 is a provisional new ureilite obtained by a meteorite dealer in Morocco in the spring of 2001. In thin section, NWA1586 displays the typical monomict ureilite texture with abundant triple junctions, curved intergranular boundaries and coarse grain sizes (1-2 mm average grain size with one or two grains up to 5 mm in length, Figure 1). Modal silicate mineralogy is 75% olivine: 25% pyroxene determined by image analysis of an electronprobe stage rastered, Mg x-ray map of the entire thin section. The olivine cores are homogeneous and Fo79 (n=61). Olivine displays prominent reduction rims that contain mg-rich olivine (Fo97; n=3) and finely dispersed grains of metal. The pyroxene is dominantly pigeonite of mg# 80 (calculated as Mg/Mg+Fe) and Wo 11 (n=103). Pigeonite rims show no reduction. The intergranular boundaries contain significant amounts of carbon.