mineral

Orthoclase Feldspar

Orthoclase (KAlSi3O8)

Hardness: 6.0 (Mohs scale); Color: Pink to flesh-colored; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Two directions at 90 degrees; Specific gravity: 2.55-2.63.

Hardness: 6
Color: Pink to flesh-colored
Luster: Vitreous to pearly

Identified March 24, 2026More mineral →

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Physical properties

Hardness: 6.0 (Mohs scale); Color: Pink to flesh-colored; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Two directions at 90 degrees; Specific gravity: 2.55-2.63.

Formation & geological history

Formed in igneous environments (granitic pegmatites and plutonic rocks) through the crystallization of magma. It is a fundamental component of Earth's crust across various geological ages.

Uses & applications

Used in the manufacture of glass and ceramics (as a flux), as a constituent in porcelain, and occasionally as a gemstone (moonstone variety). Also used in heavy-duty scouring soaps.

Geological facts

Orthoclase is the mineral that defines '6' on the Mohs scale of mineral hardness. It is one of the most abundant minerals in the Earth's continental crust.

Field identification & locations

Identify in the field by its distinct salmon-pink color, blocky cleavage planes at right angles, and its inability to be scratched by a steel knife. Commonly found in granite outcroppings and river gravels.