mineral

Potassium Feldspar

Orthoclase (KAlSi3O8)

Hardness: 6 (Mohs scale), Color: Pink, salmon, or peach-orange, Luster: Vitreous to pearly, Crystal structure: Monoclinic, Cleavage: Two planes at nearly 90 degrees, Specific Gravity: 2.55-2.63

Identified June 23, 2026More mineral →

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Physical properties

Hardness: 6 (Mohs scale), Color: Pink, salmon, or peach-orange, Luster: Vitreous to pearly, Crystal structure: Monoclinic, Cleavage: Two planes at nearly 90 degrees, Specific Gravity: 2.55-2.63

Formation & geological history

Commonly formed in igneous rocks like granite and syenite through the cooling of silica-rich magma; also found in metamorphic rocks and as a constituent of some sandstones.

Uses & applications

Used in the manufacturing of glass and ceramics (as a flux), as a mild abrasive in scouring powders, and occasionally as a gemstone (moonstone varieties).

Geological facts

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

Field identification & locations

Identify by its blocky shape, pinkish/flesh color, and pearly luster on cleavage faces. It will scratch glass but cannot be scratched by a steel knife. Commonly found in mountainous regions or riverbeds with granite outcroppings.