mineral

Orthoclase Feldspar

KAlSi3O8 (Potassium Aluminum Silicate)

Hardness: 6 on Mohs scale; Color: typically salmon-pink to reddish-white; Luster: vitreous to pearly; Crystal structure: Monoclinic; Cleavage: two planes meeting at 90 degrees; Specific Gravity: 2.55–2.63

Hardness: 6 on Mohs scale
Color: typically salmon-pink to reddish-white
Luster: vitreous to pearly

Identified May 31, 2026More mineral →

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Physical properties

Formation & geological history

Forms in igneous rocks like granite and syenite through the crystallization of cooling magma. It is also found in metamorphic rocks like gneiss and can be a component of sedimentary arkose sandstones.

Uses & applications

Primary raw material for the manufacture of glass and ceramics (as a flux to lower melting points); also used as a mild abrasive in scouring powders and occasionally as a gemstone in translucent varieties.

Geological facts

Orthoclase is one of the ten index minerals in the Mohs scale of mineral hardness. The name is derived from the Greek words for 'straight fracture,' referring to its two cleavage planes at right angles to each other.

Field identification & locations

Identify in the field by its distinctive pinkish color and right-angle cleavage. It is extremely common in continental crust and can be found worldwide in granitic mountain ranges.

Other mineral specimens

See all

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

Biotite Schist

Biotite-rich Schist [K(Mg,Fe)3AlSi3O10(F,OH)2]

metamorphic

Green Apatite on Albite

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

mineral