mineral

Orthoclase Feldspar

Orthoclase (KAlSi3O8)

Hardness: 6 on Mohs scale; Color: Pink, flesh-red, or off-white; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Two directions at 90 degrees; Specific Gravity: 2.55-2.63.

Hardness: 6 on Mohs scale
Color: Pink, flesh-red, or off-white
Luster: Vitreous to pearly

Identified March 29, 2026More mineral →

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Physical properties

Hardness: 6 on Mohs scale; Color: Pink, flesh-red, or off-white; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Two directions at 90 degrees; Specific Gravity: 2.55-2.63.

Formation & geological history

Formed in igneous environments like granites and pegmatites, as well as in some metamorphic rocks. It crystallizes from cooling magma and can be found in formations ranging from the Precambrian era to the Cenozoic.

Uses & applications

A major component in the manufacture of glass, ceramics, and enamels. It is also used as an abrasive in scouring powders and occasionally polished for use as a gemstone (such as moonstone).

Geological facts

Orthoclase takes its name from the Greek for 'straight fracture' because its two cleavage planes are at right angles. It is one of the most abundant minerals in the Earth's crust.

Field identification & locations

Identify in the field by its blocky habit, pinkish color, and its ability to scratch glass but be scratched by hardened steel. It is commonly found in the Rocky Mountains (USA), Italy, and Madagascar.