mineral

Feldspar (Orthoclase)

Potassium Feldspar (KAlSi3O8)

Hardness: 6 on Mohs scale; Color: Pink, reddish-brown, or tan; 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, reddish-brown, or tan
Luster: Vitreous to pearly

Identified June 17, 2026More mineral →

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Physical properties

Hardness: 6 on Mohs scale; Color: Pink, reddish-brown, or tan; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Two directions at 90 degrees; Specific Gravity: 2.55-2.63

Formation & geological history

Formed primarily in igneous rocks like granite and syenite through the cooling of magma, as well as in metamorphic rocks like gneiss. It is one of the most abundant minerals in the Earth's crust.

Uses & applications

Used in the manufacture of glass and ceramics (porcelain), as a filler in paints and plastics, and occasionally as a gemstone (moonstone) when of high quality.

Geological facts

Feldspar makes up about 41% of the Earth's continental crust by weight. The name is derived from the German 'Feldspat', meaning 'field spar'.

Field identification & locations

Identify in the field by its blocky cleavage, pinkish hue, and hardness (it can scratch glass but not quartz). It is found globally in mountainous regions with granitic bedrock.