mineral

Orthoclase Feldspar

Orthoclase (KAlSi3O8)

Hardness: 6 on Mohs scale; Color: typically pink, flesh-colored, or white; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Two directions at 90 degrees; Specific Gravity: 2.55–2.63.

Hardness: 6 on Mohs scale
Color: typically pink, flesh-colored, or white
Luster: Vitreous to pearly

Identified March 25, 2026More mineral →

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Physical properties

Formation & geological history

Formed through the cooling and crystallization of felsic magmas in plutonic environments (like granite) or in pegmatites. It is a common constituent of the Earth's crust across various geological ages.

Uses & applications

Used in the manufacture of glass and ceramics (as a flux) and sometimes used as a gemstone (moonstone) or in decorative carvings.

Geological facts

Orthoclase is one of the ten defining minerals of the Mohs scale of hardness. The name is derived from the Greek words 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, and hardness that can scratch glass but is scratched by quartz. Commonly found in granitic mountain ranges and mining tailings.