Silicate perovskite

Silicate perovskite is the term given to (Mg,Fe)SiO₃ (also known as bridgmanite) and CaSiO₃ (calcium silicate) when arranged in a perovskite structure. Silicate perovskites are mainly found in the lower part of Earth's mantle, between about 670 and 2,700 km (420 and 1,680 mi). They are thought to form the main mineral phases, together with ferropericlase.

Natural silicate perovskite was discovered in a heavily shocked meteorite. In 2014, the Commission on New Minerals, Nomenclature and Classification (CNMNC) of the International Mineralogical Association (IMA) approved the name bridgmanite for perovskite-structured (Mg,Fe)SiO₃, in honor of physicist Percy Bridgman, who won the Nobel Prize in Physics in 1946 for his high-pressure research.

Silicate perovskite may form up to 93% of the lower mantle, and the magnesium iron form is considered to be the most abundant mineral in the Earth, making up 38% of its volume.

Under the very high pressures of the lowermost mantle, below about 2,700 km (1,700 mi), the silicate perovskites are replaced by post-perovskite.

The physical properties of silicate perovskites under lower mantle conditions, such as seismic velocity, are studied experimentally using laser-heated diamond anvil cells. Naturally occurring silicate perovskites cannot be studied as they are unstable at the Earth's surface.

The perovskite structure (first identified in the mineral perovskite) occurs in substances with the general formula ABX₃, where A is a metal that forms large cations, B is another metal that forms smaller cations and X is typically oxygen. The structure may be cubic, but only if the relative sizes of the ions meet strict criteria. Typically, substances with the perovskite structure show lower symmetry, owing to the distortion of the crystal lattice and silicate perovskites in the orthorhombic crystal system.

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