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High-pressure form of MgSiO3 with a stacked SiO6-octahedral sheet structure that is a major component of the D” layer in Earth. Unlike perovskite, the octahedra formed by oxygen ions around the 4+ cation have differing orientations. Postperovskite forms from perovskite at conditions exceeding 125 gigapascals and 2500 K, which corresponds to a depth of ~2700 km (near the base of the mantle).The transition results in an increase in density of 1.0 to 1.2%. Incorporation of Fe into the structure greatly reduces the pressure needed for the transition. The perovskite-postperovskite phase transition probably produces the D” seismic discontinuity located just above the core-mantle boundary.

***Need references for relationship to meteorites***

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