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Periclase

Periclase
Category	Oxide mineral
Chemical formula	MgO
Identification
Color	Colorless, grayish white, yellow, brownish yellow, green, black
Crystal habit	Granular, generally occurs as anhedral to subhedral crystals in matrix
Crystal system	Isometric - Hexoctahedral
Cleavage	{001} perfect; {111} imperfect, may exhibit parting on {011}
Fracture	Brittle to conchoidal
Mohs Scale hardness	6
Luster	Vitreous
Optical Properties	Isotropic
Streak	White
Specific gravity	3.67 - 3.9
Diaphaneity	Transparent to translucent
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).

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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.