mineral

Orthoclase Feldspar (Potassium Feldspar)

KAlSi3O8 (Potassium Aluminum Silicate)

Hardness: 6.0 on Mohs scale; Color: Pinkish-orange, salmon, or tan; Luster: Vitreous to pearly on cleavage surfaces; Crystal Structure: Monoclinic; Cleavage: Two directions at nearly 90 degrees; Specific Gravity: 2.55-2.63

Hardness: 6
Color: Pinkish-orange, salmon, or tan
Luster: Vitreous to pearly on cleavage surfaces

Identified April 27, 2026More mineral →

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Physical properties

Formation & geological history

Formed through the cooling of silica-rich igneous magmas (granites, pegmatites) and within metamorphic rocks like gneiss. This specimen appears water-worn, likely from a fluvial (river) or glacial environment.

Uses & applications

Used in the manufacture of glass, ceramics (enamel and porcelain), and as an abrasive in scouring powder. Transparent/vibrant varieties are used as gemstones (e.g., Moonstone).

Geological facts

Orthoclase is one of the ten index minerals in the Mohs scale of mineral hardness. It is the defining mineral for a hardness of 6. It is a primary constituent of the Earth's continental crust.

Field identification & locations

Identify in the field by its distinct salmon-pink color, blocky cleavage planes that reflect light, and its inability to be scratched by a steel knife (but can be scratched by quartz). Commonly found in granite outcrops and creek beds.

Other mineral specimens

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Sandstone (with potential mineral staining/concretions)

Arenite (SiO2 based)

sedimentary

Schist

Metamorphic

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