Potassium Feldspar (Orthoclase)

Physical Properties

Hardness: 6 (Mohs scale); Color: Salmon pink, flesh-toned, or peach; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Two directions at 90 degrees; Specific Gravity: 2.55–2.63.

Formation & Geological History

Primary constituent of igneous rocks like granite and pegmatite. Forms during the cooling of magma. This specific specimen appears to be from a pegmatitic or granitic source.

Uses & Applications

Used in the manufacture of glass, ceramics, and enamels. Sometimes used as an abrasive in scouring powders. Gem-quality varieties like moonstone are used in jewelry.

Geological Facts

Orthoclase is one of the ten index minerals on the Mohs scale of mineral hardness. It is one of the most abundant minerals in the Earth's crust.

Field Identification & Locations

Identify by its distinctive salmon-pink color and right-angle cleavage planes. Commonly found in mountain ranges with exposed granite batholiths. It lacks the 'striations' (fine parallel lines) found on plagioclase feldspar.

Identified on: 4/27/2026

Mode: Standard