mineral

Orthoclase Feldspar

Orthoclase (KAlSi3O8)

Hardness: 6 (Mohs scale); Color: Pink to salmon-orange; Luster: Vitreous to pearly; Crystal Structure: Monoclinic; Cleavage: Two planes at 90 degrees; Specific Gravity: 2.55-2.63.

Hardness: 6 (Mohs scale)
Color: Pink to salmon-orange
Luster: Vitreous to pearly

Identified March 20, 2026More mineral →

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Physical properties

Hardness: 6 (Mohs scale); Color: Pink to salmon-orange; Luster: Vitreous to pearly; Crystal Structure: Monoclinic; Cleavage: Two planes at 90 degrees; Specific Gravity: 2.55-2.63.

Formation & geological history

Formed as a primary mineral in igneous rocks like granite and pegmatite through the cooling of silica-rich magma; also found in metamorphic rocks. Exists across many geological eras.

Uses & applications

Used in the manufacturing of glass and ceramics (as a flux), in the production of scouring powders, and occasionally as a gemstone (Moonstone is a variety of Orthoclase).

Geological facts

Orthoclase is one of the most common minerals in the Earth's crust. The name comes from the Greek 'orthos' (straight) and 'klasis' (fracture), referring to its cleavage at right angles.

Field identification & locations

Identify in the field by its distinct pinkish color, 90-degree cleavage planes, and hardness that can scratch glass but is scratched by quartz. Commonly found in granitic mountain ranges and pegmatite deposits.