mineral

Potassium Feldspar (Orthoclase)

KAlSi3O8

Hardness: 6 (Mohs scale); Color: Pink to reddish-orange (flesh-colored); Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Two planes at right angles; Specific gravity: 2.55-2.63

Hardness: 6 (Mohs scale)
Color: Pink to reddish-orange (flesh-colored)
Luster: Vitreous to pearly

Identified May 29, 2026More mineral →

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Physical properties

Hardness: 6 (Mohs scale); Color: Pink to reddish-orange (flesh-colored); Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Two planes at right angles; Specific gravity: 2.55-2.63

Formation & geological history

Commonly forms in igneous rocks like granite and pegmatites through the cooling of magma, as well as in metamorphic rocks like gneiss. It is a major constituent of the Earth's crust.

Uses & applications

Used in the manufacture of glass and ceramics (porcelain), as a filler in paints and plastics, and in crushed form for road construction. Gem-quality varieties like moonstone are used in jewelry.

Geological facts

Orthoclase is one of the ten index minerals in the Mohs scale of mineral hardness. Its name comes from the Greek words for 'straight fracture', referring to its two cleavage planes at right angles.

Field identification & locations

Look for its characteristic 'flesh-pink' color and its ability to scratch glass but be scratched by a steel file. It often exhibits a blocky shape due to its cleavage. Commonly found in mountainous regions with granitic bedrock.