Periclase
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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. In nature it usually forms a solid solution with wüstite and is... Wikipedia
Formula: MgO
Cleavage: perfect, imperfect, may exhibit parting on
Color: Colorless, grayish white, yellow, brownish yellow, green, black
Crystal class: Hexoctahedral (m3m); H-M symbol: (4/m 3 2/m)
Crystal habit: Granular, generally occurs as anhedral to subhedral octahedral crystals in matrix
Crystal system: Isometric
Luster: Vitreous