{{Infobox mineral | name = Periclase | category = Oxide mineral | boxwidth = | boxbgcolor = | image = | imagesize = | caption = | formula = MgO | molweight = | color = Colorless, grayish white, yellow, brownish yellow, green, black | habit = Granular, generally occurs as anhedral to subhedral crystals in matrix | system = Isometric - Hexoctahedral | twinning = | cleavage = {001} perfect; {111} imperfect, may exhibit parting on {011} | fracture = Brittle to conchoidal | mohs = 6 | luster = Vitreous | refractive = | opticalprop = Isotropic | birefringence = | pleochroism = | streak = White | gravity = 3.67 - 3.9 | density = | melt = | fusibility = | diagnostic = | solubility = | diaphaneity = Transparent to translucent | other = Fluorescent, Long UV=light yellow. | references = }} Periclase 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).

The old term for the mineral is magnesia. Stones from the Magnesia region in ancient Anatolia contained both magnesium oxide and hydrated magnesium carbonate as well as iron oxides (such as magnetite). Thus these stones, called Stones from Magnesia in antiquity, with their unusual magnetic properties were the reason the terms magnet and magnetism were coined. Periclase is usually found in marble and pure periclase is colorless.

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