Class : Oxides and hydroxides
    Subclass : Oxides
    Crystal system : Cubic
    Chemistry : MgO
    Rarity : Uncommon

Periclase is a rare oxide formed by thermal metamorphism, mainly in dolomites enclosed in lavas, more rarely in marbles in contact with plutonic rocks. Its name comes from the Greek peri (around) and klasis (break) because of its perfect cubic cleavage. Periclase generally occurs in small, more or less rounded grains, rarely in octahedral crystals. It is colorless to white-gray, sometimes brownish to yellow-brown to greenish when it contains a little iron (less than 10% Feo). Despite its very refractory nature, periclase easily alters into brucite and hydromagnesite.

Main photo : Periclase from Mount Somma, Naples, Italy © Christophe Boutry

No twin are known for this mineral species, however epigenized fossil corals in periclase are described in the Devonian limestone and dolomite enclaves of the Arensberg basanite quarry (Eifel, Germany).

No fakes listed for this mineral species.