Y-791199, 81-1: Diogenite (B)

          This specimen is similar to the Y-75032-type achondrite, but the crystalline portion is more abundant in hand specimen. In two thin sections, brecciated areas are also small and form veins filling the interstices of the two crystalline clasts of pyroxene. Plagioclase (An90 to An82) and chromite grains up to 0.3 mm in diameter are present in the vein matrix. The pyroxene compositions cluster around Ca_2.5Mg_64.5Fe_33.0. The two crystalline clasts are present. A pyroxenite clast, 5.8 x 3.3 mm in size, consists of coarse-grained orthopyroxene up to 3 mm in diameter with thin blebby curtain-like inclusions of augite aligned along the c direction, and of three small triangular plagioclase grains (An_74-81) at the interstices of grain boundaries of pyroxene. The pyroxene may originally have been low-Ca pigeonite. Modal abundance of this Na-rich plagioclase in the clast is 1%. An orthopyroxenite clast, 5.4 x 1.5 mm in size, possibly contains primary orthopyroxene with fine regular lamellae and fine chromite inclusions. Many tiny chromite grains decorate subgrain boundaries. The bulk chemical composition of the pyroxene in another clast is more Ca-rich and Fe-rich than that of the orthopyroxenite clast. Modal abundance of minerals in a thin section are: possible low-Ca inverted pigeonite, 49% (area), orthopyroxene 21%, matrix 29% (fine mineral fragments and glass), and plagioclase 0.6%. This specimen has more predominant diogenitic features because of more pyroxene.