mineral

Potassium Feldspar (Orthoclase)

KAlSi3O8 (Potassium Aluminum Silicate)

Hardness: 6 on Mohs scale; Color: typically salmon pink, white, or cream; 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: typically salmon pink, white, or cream
Luster: Vitreous to pearly

Identified June 19, 2026More mineral →

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Physical properties

Formation & geological history

Commonly forms in plutonic igneous rocks like granite and syenite through the slow cooling of magma. It can also form during metamorphism in rocks like gneiss and schist. Formation occurs across various geological eras wherever felsic magmatism is present.

Uses & applications

Widely used in the manufacture of glass and ceramics (as a flux) and as a mild abrasive. High-quality varieties like moonstone or sunstone are used in jewelry.

Geological facts

Orthoclase is one of the ten defining minerals of the Mohs scale of mineral hardness. It is one of the most abundant minerals in the Earth's crust.

Field identification & locations

Identify in the field by its characteristic salmon pink color and two-directional cleavage at right angles. Commonly found in granitic mountain ranges and pegmatites worldwide.

Other mineral specimens

See all

Sandstone (with potential mineral staining/concretions)

Arenite (SiO2 based)

sedimentary

Schist

Metamorphic

Epidote

Epidote | Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH)

metamorphic

Nephrite Jade

Nephrite

Mineral/Rock

Banded Gneiss (River Rock/Pebble)

Gneiss (specifically a banded variety often found as a river rock)

Metamorphic Rock

Green Apatite on Albite

Fluorapatite [Ca5(PO4)3F] on Albite [Na(AlSi3O8)]

mineral