Mineralogy of Almahata Sitta ureilites (MS-MU-011 and MS-MU-012)

Abstract

MS-MU-011 and MS-MU-012 of Almahata Sitta meteorite are O-isotopically ureilitic, but are trachyandesite and plagioclase-bearing, respectively. Fe³⁺ ratios of feldspar in MS-MU-011 (SR-XANES) are up to 0.48, suggesting crystallization under an oxidizing condition. Our MS-MU-012 does not contain plagioclase, but the reduction rim of olivine gives a fast cooling rate (0.2 ^oC/hr), corresponding to break-up of the ureilite parent body. In MS-MU-012 plagioclase somehow escaped from being removed.