Ferropericlase
Ferropericlase or magnesiowüstite is a magnesium/iron oxide ((Mg,Fe)O) that is interpreted to be one of the main constituents of the Earth's lower mantle together with silicate perovskite, a magnesium/iron silicate with a perovskite structure. Ferropericlase has been found as inclusions in a few natural diamonds. An unusually high iron content in one suite of diamonds has been associated with an origin from the lowermost mantle.[1]
Spin transition zone
Changes in the spin state of electrons in iron in mantle minerals has been studied experimentally in ferropericlase. Samples are subject to the conditions of the lower mantle in a laser-heated diamond anvil cell and the spin-state is measured using synchrotron X-ray spectroscopy. Results indicate that the change from a high to low spin state in iron occurs with increasing depth over a range from 1000 km to 2200 km.[2] The change in spin state is expected to be associated with a higher than expected increase in density with depth.