mineral

Orthoclase Feldspar

KAlSi3O8 (Potassium Aluminum Silicate)

AI-generated identification · may be incorrect

Hardness: 6 on Mohs scale; Color: Pink, salmon, or peach; 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, salmon, or peach
Luster: Vitreous to pearly

Identified June 28, 2026More mineral →

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Physical properties

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

Formation & geological history

Formed in igneous rocks like granite and syenite through slow cooling of magma, as well as in metamorphic rocks like gneiss. Found in pegmatites globally.

Uses & applications

Used primarily in the manufacture of glass and ceramics, as a filler in paint and rubber, and occasionally as a gemstone (moonstone variety).

Geological facts

Orthoclase is one of the ten defining minerals on the Mohs scale of mineral hardness. It was named from the Greek words for 'straight fracture,' referring to its two cleavage planes at right angles.

Field identification & locations

Identify in the field by its pinkish color, 90-degree cleavage, and hardness (it can scratch glass but is scratched by quartz). Commonly found in mountain ranges with high granite content.