mineral

Orthoclase Feldspar

KAlSi3O8 (Potassium aluminum silicate)

Hardness: 6 on Mohs scale; Color: typically salmon-pink to flesh-red; 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: typically salmon-pink to flesh-red
Luster: Vitreous to pearly

Identified May 7, 2026More mineral →

Identify your own rocks.

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

App Store Google Play

Physical properties

Hardness: 6 on Mohs scale; Color: typically salmon-pink to flesh-red; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Two directions at 90 degrees; Specific Gravity: 2.55-2.63.

Formation & geological history

Forms primarily in igneous rocks like granite and syenite through the cooling of magma, as well as in metamorphic rocks like gneiss. It is a major component of the Earth's continental crust.

Uses & applications

Used in the manufacture of glass and ceramics (porcelain); sometimes used as a mild abrasive in scouring powders; gem-quality varieties like moonstone are used in jewelry.

Geological facts

Orthoclase is one of the index minerals for level 6 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 distinct pinkish-orange color, 90-degree cleavage planes, and hardness (it can scratch glass but is scratched by quartz). Commonly found in granitic batholiths and pegmatites 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