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Mineralpedia Details for Orthoclase

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Orthoclase

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

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

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. 

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