Mineral

Orthoclase Feldspar

Orthoclase (KAlSi3O8)

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

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

Identified March 8, 2026More mineral →

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Physical properties

Hardness: 6 on Mohs scale; Color: Pink, fleshy, or salmon-colored; Luster: Vitreous to pearly; Crystal structure: 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 environments or within pegmatites. It is a primary constituent of granites and other felsic igneous rocks.

Uses & applications

A major ingredient in the manufacturing of ceramics and glass (used as a flux). Also used as an abrasive in scouring powders and occasionally as a gemstone (such as moonstone).

Geological facts

Orthoclase is one of the most abundant minerals in the Earth's continental crust. Its name comes from the Greek 'orthos' (straight) and 'klasis' (fracture), referring to its two cleavage planes at right angles to each other.

Field identification & locations

Identify in the field by its distinct pink color, pearly luster, and two planes of cleavage at 90 degrees. Commonly found in granite outcroppings and pegmatite dikes worldwide.