MgSiO3

MgSiO3 is a magnesium silicate with a 1:1:3 ratio of Mg, Si, and O. In geology it is best known as enstatite, the magnesium endmember of the pyroxene group. Enstatite is a common rock-forming mineral in ultramafic rocks such as peridotites and occurs in various meteorites; natural samples are often iron-bearing, written as (Mg,Fe)SiO3.

Crystal structure and polymorphism: At ambient pressure, enstatite has an orthorhombic crystal structure. Under higher temperatures or pressures, MgSiO3 can form different polymorphs, including clinoenstatite, and high-density forms become stable in planetary interiors. At the extreme pressures of Earth’s lower mantle, MgSiO3 adopts a perovskite-structured phase known as bridgmanite (Mg,Fe)SiO3, which is widely considered the most abundant mineral in that region. At still higher pressures near the core–mantle boundary, post-perovskite MgSiO3 is expected and has been implicated in seismic observations.

Geological significance: MgSiO3-bearing phases are central to models of mantle composition and dynamics. The transition among enstatite, bridgmanite, and post-perovskite affects elastic properties and seismic wave speeds, helping to explain certain seismic discontinuities in the deep Earth and to constrain mantle temperature and composition.

Occurrence and synthesis: In nature, MgSiO3 occurs primarily as enstatite in mantle-derived rocks and in meteorites, with iron and other cations commonly substituting for magnesium. It can be synthesized in laboratory high-pressure, high-temperature experiments to study its properties under conditions relevant to the Earth and other planetary interiors.