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.
