periclase

{{Infobox mineral | name = Periclase | category = Oxide minerals | boxwidth = | boxbgcolor = | image = Periclase - Ronneburg, Thuringia1.jpg | imagesize = 260px | caption = White to light greenish periclase with black srebrodolskite from Ronneburg, Thuringia, Germany (Picture size 5 mm) | formula = MgO | IMAsymbol = Per | molweight = | strunz = 4.AB.25 | system = Isometric | class = Hexoctahedral (mm)H-M symbol: (4/m 2/m) | symmetry = Fmm | unit cell = 4.21 Å; Z = 4 | color = Colorless, grayish white, yellow, brownish yellow, green, black | habit = Granular, generally occurs as anhedral to subhedral octahedral crystals in matrix | twinning = | cleavage = {001} perfect; {111} imperfect, may exhibit parting on {011} | fracture = Conchoidal | tenacity = Brittle | mohs = 6 | luster = Vitreous | refractive = n = 1.735–1.745 | opticalprop = Isotropic | birefringence = | pleochroism = | streak = White | gravity = 3.56–3.68 (meas.) 3.58 (calc.) | density = | melt = | fusibility = | diagnostic = | solubility = | diaphaneity = Transparent to translucent | other = Fluorescent, long UV=light yellow. | references = }}

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.