mineral

Feldspar (Orthoclase / Alkali Feldspar)

KAlSi3O8 (Potassium Feldspar / Orthoclase)

Hardness: 6 on Mohs scale. Color: Salmon-pink, reddish-brown, tan, to orange. Luster: Vitreous to pearly on cleavage faces. Cleavage: Two directions intersecting at or near 90 degrees. Crystal system: Monoclinic/Triclinic. Specific gravity: 2.56 - 2.58.

Hardness: 6 on Mohs scale
Color: Salmon-pink, reddish-brown, tan, to orange
Luster: Vitreous to pearly on cleavage faces

Identified July 24, 2026More mineral →

Explore Feldspar (Orthoclase / Alkali 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 during the crystallization of igneous rocks (like granite and pegmatite) and metamorphic rocks. It crystallizes from silicate magma at high temperatures and pressures deep within the Earth's crust.

Uses & applications

Used extensively in the manufacture of ceramics, porcelain, enamel, and glass. High-quality transparent or chatoyant varieties (like moonstone or sunstone) are cut as gemstones. Fine powders are used as abrasives.

Geological facts

Feldspars are the most abundant group of minerals in the Earth's continental crust, making up roughly 60% of terrestrial rocks. Pink to reddish feldspars owe their color to micro-inclusions of iron oxide (hematite).

Field identification & locations

Identified by its distinctive salmon-pink to reddish tint, vitreous luster, and two prominent cleavage planes meeting at nearly right angles. Commonly found worldwide in granitic terrains, gravel beds, and pegmatite deposits.

Other mineral specimens

See all

Sandstone (with potential mineral staining/concretions)

Arenite (SiO2 based)

sedimentary

Schist

Metamorphic

Sandstone with Mineral Veining or Crust

Sedimentary Sandstone (mostly SiO2 with Fe2O3 tinting)

sedimentary

Potassium Feldspar (Orthoclase)

Orthoclase (KAlSi3O8)

mineral

Gypsum (variety Selenite or Alabaster)

Calcium sulfate dihydrate (CaSO4·2H2O)

Mineral

Nephrite Jade

Nephrite

Mineral/Rock