Silicate Perovskites: at depths greater than approximately 660 km in the Earth’s mantle, where pressures reach around 22 GPa, mantle Olivine (high in Mg) becomes unstable and collapses, adopting a denser crystal structure similar to Perovskite, with the chemical formula (Mg,Fe)₂SiO₃. Since, in addition to Olivine, the mantle’s primary mineral assemblage includes Pyroxenes and Garnets, these too undergo lattice collapse, forming an association of three silicate Perovskites: (Mg,Fe)₂SiO₃, Al(Mg,Fe)₂SiO₃, and CaSiO₃. These mineral compounds, extremely dense and viscous and never found in surface rocks—even those of deep origin—are believed to be the most abundant minerals in the lower mantle.
