mineral

Potassium Feldspar

Orthoclase (KAlSi3O8)

Hardness: 6.0 on Mohs scale; Color: Pink, salmon, or fleshy white; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Two directions at nearly 90 degrees; Specific gravity: 2.55-2.63

Hardness: 6
Color: Pink, salmon, or fleshy white
Luster: Vitreous to pearly

Identified July 11, 2026More mineral →

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Physical properties

Formation & geological history

Forms primarily in igneous rocks like granite and syenite through the cooling of magma, as well as in metamorphic rocks and certain sedimentary deposits. Origins can date back billions of years depending on the host rock formation.

Uses & applications

Extensively used in the manufacture of glass and ceramics (as a flux), in the production of scouring powders, and occasionally as a gemstone (moonstone variant).

Geological facts

Feldspars are the most abundant group of minerals in the Earth's crust, making up about 60% of the terrestrial crust. The name 'orthoclase' comes from the Greek for 'straight fracture,' referring to its two cleavage planes.

Field identification & locations

Identify in the field by its distinct pinkish color in granitic rocks and its blocky cleavage. It is common in mountain ranges with exposed batholiths. It will not be scratched by a steel knife but can be scratched by quartz.