Crestmore California, USA — Photo: Pacific Museum of Earth from Canada · CC BY-SA 2.0
Periclase
Cubic magnesium oxide — a contact-metamorphic mineral and the refractory lining of steel furnaces.
Intro adapted from Wikipedia (CC BY-SA).
Periclase is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula MgO.
It crystallizes in the cubic crystal system (space group Fm3m). It is a member of the Rocksalt structural group.
Key properties: Mohs hardness 5.5; specific gravity 3.56–3.68; typically colorless or white or yellow or green; White streak; Vitreous luster; refractive index 1.74; optically isotropic.
IMA symbol Per, grandfathered status — known before the IMA’s founding, named in 1841.
A product of the high-temperature metamorphism of magnesian limestones and dolostone.
It is found associated with Forsterite, magnesite (Monte Somma, Italy); brucite, hydromagnesite, ellestadite (Crestmore quarry, California, USA); fluorellestadite, lime, periclase.
Its name comes from the Greek for to break around, in allusion to the perfect cubic cleavage.
Collections: Rare & Remarkable.