Mineralpedia Details for Orthoclase

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Orthoclase

Formula: K(AlSi₃)O₈
Crystal System: Monoclinic
Crystal Habit: Prismatic, Massive - Granular, Blocky
Cleavage: Perfect, Good, None
Luster: Vitreous (Glassy)
Color: colorless, greenish, grayish yellow, white, pink
Streak: white
Class: Monoclinic - Prismatic
Fracture: Uneven
Hardness: 6
WebMineral: View Orthoclase
Mindat: View Orthoclase

Orthoclase from Hirukawa, Gifu Pref., Chubu, Honshu Island, Japan

Dull, light brownish white Orthoclase crystals in aggregate to 5cm.

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Orthoclase var. adularia from Cristallina Valley, Grischun, Switzerland

Adularia is found in Alpine clefts. It is a variety of Orthoclase, the potassium feldspar found in low temperature hydrothermal veins such as the Alpine clefts of Switzerland and Italy. Adularia crystals are distinctly wedge-shaped or pseudo-rhombohedral with diamond cross-sections and almost always somewhat transparent. The crystals on this specimen are to 1.5cm.