mineral

Orthoclase Feldspar

Potassium Aluminum Silicate (KAlSi3O8)

Hardness: 6.0 on Mohs scale; Color: typically pink, flesh-colored, or tan; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Two directions at right angles; Specific Gravity: 2.55-2.63

Hardness: 6
Color: typically pink, flesh-colored, or tan
Luster: Vitreous to pearly

Identified March 16, 2026More mineral →

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Physical properties

Formation & geological history

Formed in igneous environments as a primary constituent of granite and other felsic rocks, or in metamorphic rocks. It crystallizes from cooling magma or during regional metamorphism, found in geological ages ranging from Precambrian to Cenozoic.

Uses & applications

Industry: manufacture of glass and ceramics (as a flux); Construction: aggregate and decorative stone; Collecting: gem-quality varieties like moonstone are used in jewelry.

Geological facts

Orthoclase is one of the most common minerals in the Earth's crust. It is a defining mineral for level 6 on the Mohs scale of mineral hardness. The name comes from the Greek for 'straight fracture,' referring to its two cleavage planes at right angles.

Field identification & locations

Identify in the field by its distinct pink/salmon color, 90-degree cleavage planes, and lack of striations compared to plagioclase. Extremely common in granitic mountain ranges and gravel deposits.

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Mineral/Rock

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