Grossmanite, CaTi (super 3+) AlSiO (sub 6) , a new pyroxene from the Allende Meteorite

Grossmanite, Ca(Ti (super 3+) ,Mg,Ti (super 4+) )AlSiO (sub 6) with an end-member formula CaTi (super 3+) AlSiO (sub 6) , is a new member of the Ca clinopyroxene group, where the trivalent cations are dominant in the M1 site with Ti (super 3+) being the dominant trivalent cation. It occurs as micrometer-sized crystals along with spinel and perovskite in a melilite host in Ca-, Al-rich refractory inclusions from the Allende meteorite. The mean chemical composition determined by electron microprobe analysis of the type material is (wt%) SiO (sub 2) 27.99, Al (sub 2) O (sub 3) 24.71, CaO 24.58, Ti (sub 2) O (sub 3) 10.91, TiO (sub 2) 6.68, MgO 4.45, Sc (sub 2) O (sub 3) 0.43, V (sub 2) O (sub 3) 0.19, ZrO (sub 2) 0.13, FeO 0.08, Cr (sub 2) O (sub 3) 0.03, sum 100.20. Its empirical formula calculated on the basis of 6 O atoms is Ca (sub 1.00) [(Ti (sub 0.35) (super 3+) Al (sub 0.18) Sc (sub 0.01) V (sub 0.01) (super 3+) ) (sub Sigma 0.55) Mg (sub 0.25) Ti (sub 0.19) (super 4+) ] (sub Sigma 1.00) (Si (sub 1.07) Al (sub 0.93) ) (sub Sigma 2.00) O (sub 6) . Grossmanite is monoclinic, C2/c; a=9.80 Aa, b=8.85 Aa, c=5.36 Aa, beta =105.62 degrees , V=447.70 Aa (super 3) , and Z=4. Its electron back-scatter diffraction pattern is an excellent match to that of Ti (super 3+) -rich pyroxene with the C2/c structure. The five strongest calculated X-ray powder diffraction lines are [d spacing in Aa, (I), hkl] 2.996 (100) (221), 2.964 (31) (310), 2.581 (42) (002), 2.600 (28) (131), 2.535 (47) (221). The name is for Lawrence Grossman, a cosmochemist at the University of Chicago.