Ferropericlase
Ferropericlase or magnesiowüstite is a magnesium/iron oxide with the chemical formula (Mg,Fe)O that is interpreted to be one of the main constituents of the Earth's lower mantle together with the silicate perovskite ((Mg,Fe)SiO3), a magnesium/iron silicate with a perovskite structure. Ferropericlase has been found as inclusions in a few natural diamonds.