mineral

Orthoclase Feldspar

KAlSi3O8 (Potassium Aluminum Silicate)

Hardness: 6.0 on Mohs scale; Color: Pink, flesh, white, or gray; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Two directions at 90 degrees; Specific Gravity: 2.55-2.63.

Hardness: 6
Color: Pink, flesh, white, or gray
Luster: Vitreous to pearly

Identified April 7, 2026More mineral →

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Physical properties

Hardness: 6.0 on Mohs scale; Color: Pink, flesh, white, or gray; 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 environments such as granites, pegmatites, and syenites through the cooling of silica-rich magma; also appears in metamorphic rocks like gneiss.

Uses & applications

Used in the manufacture of glass, ceramics, and enamels. High-quality specimens like Moonstone 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 by its light color (often pinkish), 90-degree cleavage, and inability to be scratched by a steel knife but can scratch glass. Common in mountain ranges with granitic bedrock.

Other mineral specimens

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Sandstone (with potential mineral staining/concretions)

Arenite (SiO2 based)

sedimentary

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

Epidote

Epidote - Ca2(Al2,Fe3+)3(SiO4)3(OH)

mineral