mineral

Feldspar (Orthoclase)

Orthoclase (KAlSi3O8)

Hardness: 6 on Mohs scale; Color: Pink, salmon, or fleshy red; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Perfect in two directions at 90 degrees; Specific gravity: 2.55-2.63

Hardness: 6 on Mohs scale
Color: Pink, salmon, or fleshy red
Luster: Vitreous to pearly

Identified June 23, 2026More mineral →

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Physical properties

Formation & geological history

Forms primarily in igneous rocks like granite and pegmatites through the crystallization of magma, as well as in some metamorphic rocks. It is a major component of the Earth's continental crust.

Uses & applications

Used in the manufacture of glass and ceramics (porcelain), as a filler in paints and plastics, and occasionally as a gemstone (such as moonstone).

Geological facts

Feldspar is the most abundant mineral group in the Earth's crust. Orthoclase derives its name from the Greek for 'straight fracture,' referring to its two cleavage planes at right angles.

Field identification & locations

Identify in the field by its pinkish color, its inability to be scratched by a steel knife, and its distinct 90-degree cleavage planes. Commonly found in granitic terrains worldwide.