mineral

Orthoclase Feldspar

KAlSi3O8 (Potassium Aluminum Silicate)

AI-generated identification · may be incorrect

Hardness: 6 (Mohs); Color: Salmon-pink, tan, or white; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Two planes meeting at nearly 90 degrees; Specific gravity: 2.55-2.63

Hardness: 6 (Mohs)
Color: Salmon-pink, tan, or white
Luster: Vitreous to pearly

Identified July 1, 2026More mineral →

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Physical properties

Hardness: 6 (Mohs); Color: Salmon-pink, tan, or white; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Two planes meeting at nearly 90 degrees; Specific gravity: 2.55-2.63

Formation & geological history

Formed in igneous environments like granite or pegmatite, as well as in some metamorphic rocks. Most specimens are hundreds of millions of years old, often from the Precambrian or Paleozoic eras.

Uses & applications

Used in the manufacturing of glass and ceramics (as a flux), porcelain, and occasionally used as a gemstone (Moonstone is a variety). Collectors value well-defined cleavage planes.

Geological facts

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

Field identification & locations

Identify in the field by its distinct salmon-pink color, blocky shape, and two right-angle cleavage planes. It is a major constituent of granite, frequently found in mountainous regions.