mineral

Orthoclase Feldspar

Orthoclase (KAlSi3O8)

Hardness: 6 on Mohs scale; Color: Pink, flesh-colored, or salmon; Luster: Vitreous to pearly; Crystal System: Monoclinic; Cleavage: Two directions at 90 degrees; Specific Gravity: 2.55-2.63.

Hardness: 6 on Mohs scale
Color: Pink, flesh-colored, or salmon
Luster: Vitreous to pearly

Identified April 6, 2026More mineral →

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Physical properties

Hardness: 6 on Mohs scale; Color: Pink, flesh-colored, or salmon; Luster: Vitreous to pearly; Crystal System: Monoclinic; Cleavage: Two directions at 90 degrees; Specific Gravity: 2.55-2.63.

Formation & geological history

Formed through the cooling of silica-rich magma in plutonic igneous rocks like granite and pegmatite. It is a major constituent of the Earth's continental crust.

Uses & applications

Used in the manufacture of glass, ceramics, and porcelain. High-quality varieties (like moonstone) are used in jewelry. Often used as an abrasive in scouring powders.

Geological facts

Orthoclase is one of the ten index minerals on the Mohs scale of mineral hardness. The name is derived from the Greek for 'straight fracture,' referring to its two cleavage planes at right angles to each other.

Field identification & locations

Identify by its characteristic pink/salmon color and its 'stair-step' cleavage pattern. Commonly found in granitic mountain ranges worldwide (e.g., the Rockies, Himalayas). Look for flat, shiny surfaces on broken faces.