Grossite (CaAl (sub 4) O (sub 7) ); a rare phase in terrestrial rocks and meteorites

Grossite occurs as a colourless to white, transparent, major phase in Ca,Al-rich inclusions (CAIs) from the meteorites Acfer 182, Acfer 059-El Djouf 001 and ALH85085; accessory minerals are perovskite, hibonite, melilite and spinel. It is also found in terrestrial rocks of the Hatrurim formation, Israel, where it occurs with brownmillerite and mayenite. The empirical formula of grossite derived from EPMA is (Ca (sub 1.00) Fe (sub 0.01) )Al (sub 3.99) O (sub 7) or ideally CaAl (sub 4) O (sub 7) . Indexed XRD powder data are tabulated; strongest lines 3.515(100), 4.460(43), 2.605(36), 2.440(21), 1.764(20) Aa; a 12.94, b 8.910, c 5.446 Aa, beta 107.01 degrees , V 600.1 Aa (super 3) ; space group C2/c; Z = 4; D (sub calc) 2.88 g/cm (super 3) . This Ca-dialuminate has alpha 1.6178, beta 1.6184, Gamma 1.6516, 2V<F128MV>g<F255D>12 degrees . Grossite is formed by high-T processes either in the early solar system or in argillaceous limestones. The name is in honour of Dr. S. Gross of the Geological Survey of Israel, who reported this mineral as an unnamed phase in the Hatrurim formation.