mineral

Potassium Feldspar

Orthoclase (KAlSi3O8)

Hardness: 6 on Mohs scale; Color: typically pink, tan, or reddish-brown due to iron impurities; Luster: Vitreous (glassy) to pearly; Crystal structure: Monoclinic; Cleavage: Two directions at nearly 90 degrees.

Hardness: 6 on Mohs scale
Color: typically pink, tan, or reddish-brown due to iron impurities
Luster: Vitreous (glassy) to pearly

Identified June 2, 2026More mineral →

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Physical properties

Formation & geological history

Formed as a primary mineral in igneous rocks like granite and syenite through the cooling of magma. It can also be found in metamorphic rocks and as grains in sedimentary sandstone.

Uses & applications

Widely used in the manufacture of glass and ceramics (as a flux to lower melting temperatures). Also used as an abrasive in scouring powders and occasionally as a gemstone (moonstone variant).

Geological facts

Feldspars are the most abundant mineral group in Earth's crust, making up about 60% of terrestrial rocks. The pink color in many granites, such as those in the Rocky Mountains, is due to the presence of Orthoclase.

Field identification & locations

Identify in the field by its distinct salmon-pink to flesh-red color and blocky cleavage planes. It will scratch glass but can be scratched by a masonry drill bit or quartz coordinate.