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Category Oxide minerals
(repeating unit)
Strunz classification 04.AB.25
Crystal symmetry Cubic 4/m 3 2/m
Unit cell 4.21 Å Z=4
Color Colorless, grayish white, yellow, brownish yellow, green, black
Crystal habit Granular, generally occurs as anhedral to subhedral octahedral crystals in matrix
Crystal system Isometric - Hexoctahedral

{001} perfect; {111} imperfect, may exhibit parting on

Fracture Conchoidal
Tenacity Brittle
Mohs scale hardness 6
Luster Vitreous
Streak White
Diaphaneity Transparent to translucent
Specific gravity 3.56–3.68 (meas.) 3.58 (calc.)
Optical properties Isotropic
Refractive index n = 1.735–1.745
Other characteristics Fluorescent, long UV=light yellow.
References [1][2][3]

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).

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.[3]

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 produced by metamorphism of dolomitic limestones. It readily alters to brucite under near surface conditions.[3]

In addition to its type locality, it is reported from Predazzo, Tyrol, Austria; Carlingford, County Louth, Ireland; Broadford, Skye and the island of Muck, Scotland; León, Spain; the Bellerberg volcano, Eifel district, Germany; Nordmark and Långban, Varmland, Sweden; and Kopeysk, southern Ural Mountains, Russia. In the USA it occurs at the Crestmore quarry, Riverside County, California; Tombstone, Cochise County, Arizona; Gabbs district, Nye County, Nevada. In Canada, it occurs at Oka, Quebec and in Australia, west of Cowell, Eyre Peninsula, South Australia.[1]