Magnet
Rare earth (lanthanoid) elements have a partially occupied "f" electron shell (which can accommodate up to 14 electrons). The spin of these electrons can be aligned, resulting in very strong magnetic fields, and therefore, these elements are used in compact high-strength magnets where their higher price is not a concern. The most common types of rare-earth magnets are samarium-cobalt and neodymium-iron-boron (NIB) magnets.
Perovskite (structure)
The most common mineral in the Earth is bridgmanite, a magnesium-rich silicate which adopts the perovskite structure at high pressure. As pressure increases, the SiO tetrahedral units in the dominant silica-bearing minerals become unstable compared with SiO octahedral units. At the pressure and temperature conditions of the lower mantle, the most abundant material is a perovskite-structured mineral with the formula (Mg,Fe)SiO, with the second most abundant material likely the rocksalt-structured (Mg,Fe)O oxide, periclase.