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Published October 2009 | public
Journal Article

Grossmanite, CaTi^(3+)AlSiO_6, a new pyroxene from the Allende meteorite

Abstract

Grossmanite, Ca(Ti^(3+),Mg,Ti^(4+))AlSiO_6 with an end-member formula CaTi^(3+)AlSiO_6, is a new member of the Ca clinopyroxene group, where the trivalent cations are dominant in the M1 site with Ti^(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_2 27.99, Al_(2)O_3 24.71, CaO 24.58, Ti_(2)O_3 10.91, TiO_2 6.68, MgO 4.45, Sc_(2)O_3 0.43, V_(2)O_3 0.19, ZrO_2 0.13, FeO 0.08, Cr_(2)O_3 0.03, sum 100.20. Its empirical formula calculated on the basis of 6 O atoms is Ca_(1.00)[(Ti_(0.35)^(3+)Al_(0.18)Sc_(0.01)V_(0.01_^(3+))_(Σ0.55)Mg_(0.25)Ti_(0.19_^(4+)]_(Σ1.00)(Si_(1.07)Al_(0.93))_(Σ2.00)O_6. Grossmanite is monoclinic, C2/c; a = 9.80 Å, b = 8.85 Å, c = 5.36 Å, β = 105.62°, V = 447.70 Å^3, and Z = 4. Its electron back-scatter diffraction pattern is an excellent match to that of Ti3+-rich pyroxene with the C2/c structure. The five strongest calculated X-ray powder diffraction lines are [d spacing in Å, (I), hkl] 2.996 (100) (21), 2.964 (31) (310), 2.581 (42) (002), 2.600 (28) (1[overbar]31), 2.535 (47) (221). The name is for Lawrence Grossman, a cosmochemist at the University of Chicago.

Additional Information

© 2009 Mineralogical Society of America. Manuscript received June 5, 2009; manuscript accepted June 16, 2009; manuscript handled by Bryan Chakoumakos.

Additional details

Created:
August 22, 2023
Modified:
October 19, 2023