mineral

Orthoclase Feldspar

KAlSi3O8 (Potassium Aluminum Silicate)

Hardness: 6 on Mohs scale; Color: Pink, salmon-orange, or reddish-brown; 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: Pink, salmon-orange, or reddish-brown
Luster: Vitreous to pearly

Identified July 5, 2026More mineral →

Explore Orthoclase Feldspar in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Forms in igneous rocks like granite and syenite through the cooling of magma, and in metamorphic rocks like gneiss. It is a major component of the Earth's continental crust and can form at various geological ages.

Uses & applications

Used in the manufacture of glass, ceramics (glazes and porcelain), and scouring powders. Certain varieties like moonstone are used in jewelry.

Geological facts

Orthoclase is one of the ten index minerals in the Mohs hardness scale. The word 'orthoclase' comes from the Greek 'orthos' meaning 'straight' and 'klasis' meaning 'fracture', referring to its right-angle cleavage.

Field identification & locations

Identify by its distinctive pink/salmon color and its tendency to break into blocky shapes along cleavage planes. It is ubiquitous in mountainous regions with granitic bedrock and common in river gravels near such sources.

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

Gypsum (variety Selenite or Alabaster)

Calcium sulfate dihydrate (CaSO4·2H2O)

Mineral

Nephrite Jade

Nephrite

Mineral/Rock

Granite

Granite (Phaneritic intrusive igneous rock)

igneous