mineral

Orthoclase Feldspar

KAlSi3O8 (Potassium Aluminum Silicate)

Hardness: 6.0 on Mohs scale; Color: typically salmon-pink, flesh-colored, or white; Luster: vitreous to pearly; Crystal structure: Monoclinic; Cleavage: perfect in two directions at 90 degrees; Specific Gravity: 2.55–2.63

Hardness: 6
Color: typically salmon-pink, flesh-colored, or white
Luster: vitreous to pearly

Identified March 15, 2026More mineral →

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Physical properties

Formation & geological history

Formed through the cooling of igneous magmas, particularly in granites and pegmatites. It is a major component of earth's continental crust and can also be found in high-grade metamorphic rocks.

Uses & applications

Used primarily in the manufacturing of glass and ceramics (as a flux) and as an ingredient in scouring powders. Some translucent varieties are used as gemstones (Moonstone).

Geological facts

Orthoclase is one of the ten index minerals of 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 by its salmon-pink color, blocky cleavage, and its ability to scratch glass but not quartz. Commonly found in granitic mountain ranges and as beach pebbles in areas with high erosion of continental crust.

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)]

mineral

Epidote

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

mineral