mineral

Orthoclase Feldspar

Orthoclase (KAlSi3O8)

Hardness: 6 on Mohs scale; Color: typically pink, flesh-red, or creamy white; Luster: vitreous to pearly; Crystal structure: monoclinic; Cleavage: perfect in two directions at 90 degrees; Specific gravity: 2.55-2.63

Hardness: 6 on Mohs scale
Color: typically pink, flesh-red, or creamy white
Luster: vitreous to pearly

Identified February 24, 2026More mineral →

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Physical properties

Formation & geological history

Formed through the crystallization of magma in intrusive igneous rocks like granite or metamorphic pegmatites. It is one of the most common silicate minerals in the Earth's crust, found in environments ranging from Precambrian to recent geological ages.

Uses & applications

Used in the manufacturing of ceramics and glass to reduce melting temperatures. Also used as an abrasive in scouring powders and occasionally as a gemstone (such as moonstone).

Geological facts

Orthoclase is a defining mineral for the number 6 on the Mohs scale of hardness. The name is derived from the Greek words for 'straight fracture', referring to its two cleavage planes at right angles to each other.

Field identification & locations

Identify in the field by its blocky shape, pinkish hue, and the presence of two distinct cleavage planes. Commonly found in granitic mountain ranges worldwide and in riverbeds as weathered pebbles.