Perovskite

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Term applied to A2+B4+O3 high-pressure minerals with a perovskite structure (general formula ABX3) where “A” is a metal that forms large cations such as Mg, Fe or Ca, “B” is another metal that forms smaller cations such as Si (called silicate perovskite), Ti and to a lesser degree Al, and “X” is typically oxygen. Each B4+ ion is octahedrally coordinated with six oxygen atoms, and the A2+ ion sits in the center. Although ideally a cubic structure, the actual mineral is slightly monoclinic because one unit cell angle is 90.67º. The magnesian end-member of silicate perovskite (MgSiO3 perovskite) is the most abundant mineral in the Earth’s lower mantle (and thus inaccessible for study). Only after 50+ years of searching was this important high-pressure polymorph of enstatite (MgSiO3) finally discovered and identified in nature within the shocked Tenham meteorite (as reported in 2014) and after characterization given the name bridgmanite. Interestingly, ringwoodite, the high-pressure olivine polymorph was also discovered in the Tenham meteorite in 1969. CaTiO3 perovskite is abundant within Calcium Aluminum-rich Inclusions (CAI) and the Wark-Lovering rims (WLR) that surround many CAIs1.


Some or all content above used with permission from J. H. Wittke.