Periclase is a magnesium mineral that occurs naturally in contact metamorphic rocks and is a major component of most basic refractory bricks. It is a cubic form of magnesium oxide (MgO). In nature it usually forms a solid solution with wüstite (FeO) and is then referred to as ferropericlase or magnesiowüstite.
It was first described in 1840 and named from the Greek περικλάω (to break around) in allusion to its cleavage. The type locality is Monte Somma, Somma-Vesuvius Complex, Naples Province, Campania, Italy.
Mantle occurrence
Ferropericlase makes up about 20% of the volume of the lower mantle of the Earth, which makes it the second most abundant mineral phase in that region after silicate perovskite ; it also is the major host for iron in the lower mantle. At the bottom of the transition zone of the mantle, the reaction
: γ–
transforms γ-olivine into a mixture of perovskite and ferropericlase and vice versa. In the literature, this mineral phase of the lower mantle is also often called magnesiowüstite.