Discovery of a New Garnet Mineral, Ca_3Ti_2(SiAl_2)O_(12): An Alteration Phase in Allende

Abstract

During a nanomineralogy investigation of the Allende CV3 carbonaceous chondrite, a new Ti-rich silicate, Ca_3Ti_2(SiAl_2)O_(12) with the Ia-3d garnet structure, was identified in the Type B1 Ca,Al-rich inclusion (CAI) Egg-3. Field-emission SEM with EDS and electron back-scatter diffraction and electron microprobe were used to characterize the composition and structure. Synthetic Ca_3Ti_2(SiAl_2)O_(12) is not reported. We present here the natural occurrence of Ca_3Ti_2(SiAl_2)O_(12), as a new alteration silicate in a CAI, and discuss its origin and significance for secondary processes. The mineral is currently under review by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA 2013-029). It is a new member of the schorlomite group in the garnet supergroup.

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