Jiddat al Harasis 422: A ureilite with an extremely high degree of shock melting

International audienceThe Jiddat al Harasis (JaH) 422 ureilite was found in the Sultanate of Oman; it is classified as a ureilitic impact melt breccia. The meteorite consists of rounded polycrystalline olivine clasts (35%), pores (8%), and microcrystalline matrix (57%). Clasts and matrix have oxygen isotopic values and chemical compositions (major and trace elements) characteristic of the ureilite group. The matrix contains olivine (Fo83-90), low-Ca pyroxene (En84-92Wo0-5), augite (En71-56Wo20-31), graphite, diamond, Fe-metal, sulfides, chromite, and felsic glass. Pores are partly filled by secondary Fe-oxihydroxide and desert alteration products. Pores are surrounded by strongly reduced silicates. Clasts consist of fine-grained aggregates of polygonal olivine. These clasts have an approximately 250 μm wide reaction rim, in which olivine composition evolves progressively from the core composition (Fo79-81) to the matrix composition (Fo84-87). Veins crossing the clasts comprise pyroxene, Fe-oxihydroxide, C-phases, and chromite. Clasts contain Ca-, Al-, and Cr-rich glass along olivine grain boundaries (