Mineral

Orthoclase Feldspar

Orthoclase (KAlSi3O8)

Hardness: 6 on Mohs scale; Color: Tan, flesh-pink, or greyish-white; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Two planes meeting at 90 degrees; Specific Gravity: 2.55–2.63.

Hardness: 6 on Mohs scale
Color: Tan, flesh-pink, or greyish-white
Luster: Vitreous to pearly

Identified March 16, 2026More mineral →

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Physical properties

Formation & geological history

Formed through the cooling of silica-rich magma in igneous rocks like granite and pegmatite. It can also form in metamorphic rocks through regional metamorphism. Common in geological formations of various ages, especially Precambrian shields.

Uses & applications

Used primarily in the manufacture of glass and ceramics (porcelain and glaze). Occasionally used as a gemstone (moonstone variety) and as a mild abrasive in scouring powders.

Geological facts

Orthoclase is one of the most common minerals in the Earth's crust. It is a defining mineral for the hardness of 6 on the Mohs scale. Some rare varieties show 'adularescence' and are known as Moonstone.

Field identification & locations

Identify in the field by its blocky shape and two distinct cleavage planes at 90 degrees. Commonly found in granite-rich mountain ranges or as pebbles in riverbeds. Collectors look for sharp crystal edges and consistent color.