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Post-perovskite is a high-pressure phase of magnesium silicate. It is composed of the prime oxide constituents of the Earth's rocky mantle , and its pressure and temperature for stability imply that it is likely to occur in portions of the lowermost few hundred km of Earth's mantle.
The post-perovskite phase has implications for the D′′ layer, which influences the convective mixing in the mantle responsible for plate tectonics.
Post-perovskite has the same crystal structure as the synthetic solid compound CaIrO3, and is often referred to as the "CaIrO3-type phase of MgSiO3" in the literature. The crystal system of post-perovskite is orthorhombic, its space group is Cmcm, and its structure is a stacked SiO6-octahedral sheet along the b axis. The name "post-perovskite" derives from silicate perovskite, the stable phase of MgSiO3 throughout most of Earth's mantle, which has the perovskite structure. The prefix "post-" refers to the fact that it occurs after perovskite structured MgSiO3 as pressure increases. At upper mantle pressures, nearest Earth's surface, MgSiO3 persists as the silicate mineral enstatite, a pyroxene rock forming mineral found in igneous and metamorphic rocks of the crust.