mineral

Orthoclase Feldspar

KAlSi3O8 (Potassium Aluminum Silicate)

Hardness: 6 on Mohs scale; Color: typically salmon-pink to reddish-peach; Luster: Vitreous to pearly on cleavage faces; Crystal Structure: Monoclinic; Cleavage: Two directions at 90 degrees; Specific Gravity: 2.55-2.63.

Hardness: 6 on Mohs scale
Color: typically salmon-pink to reddish-peach
Luster: Vitreous to pearly on cleavage faces

Identified April 2, 2026More mineral →

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Physical properties

Formation & geological history

Formed in igneous rocks like granite and syenite through the cooling of silica-rich magma; also found in metamorphic rocks like gneiss. It is a major constituent of the Earth's continental crust.

Uses & applications

Extensively used in the manufacture of glass and ceramics (porcelain); also used as a mild abrasive in scouring powders and occasionally as a gemstone (moonstone or sunstone varieties).

Geological facts

Orthoclase is one of the ten defining 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 in the field by its characteristic salmon-pink color, blocky cleavage, and its ability to scratch glass but be scratched by hardened steel. It is ubiquitous in granitic terrains worldwide.

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)]

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Epidote

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

mineral