mineral

Orthoclase Feldspar

KAlSi3O8 (Potassium Aluminum Silicate)

Hardness: 6 on Mohs scale; Color: typically pink, salmon-orange, or flesh-red; Luster: vitreous to pearly; Crystal structure: Monoclinic; Cleavage: two planes at 90 degrees; Specific Gravity: 2.55–2.63

Hardness: 6 on Mohs scale
Color: typically pink, salmon-orange, or flesh-red
Luster: vitreous to pearly

Identified April 1, 2026More mineral →

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Physical properties

Formation & geological history

Formed as a primary mineral in igneous rocks like granite and syenite, as well as in metamorphic rocks like gneiss. It crystallizes from cooling magma or during high-grade metamorphism.

Uses & applications

Used in the manufacture of glass and ceramics (porcelain), as a filler in paints and plastics, and occasionally as a gemstone (Moonstone is a variety).

Geological facts

Orthoclase is one of the most common minerals in the Earth's crust. It is a defining mineral for level 6 on the Mohs Hardness Scale. Its name comes from the Greek for 'straight fracture' because its two cleavage planes are at right angles.

Field identification & locations

Identify by its salmon-pink color, blocky cleavage, and hardness (will scratch glass but won't be scratched by a steel nail). It is extremely common in granitic mountain ranges worldwide.

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

Green Apatite on Albite

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

mineral

Epidote

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

mineral