Orthoclase (Potassium) Feldspar in Quartz

Physical Properties

Hardness: 6.0-6.5 on Mohs scale; Color: Pink, salmon-orange, to white; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Two directions at 90 degrees; Specific gravity: 2.55-2.63.

Formation & Geological History

Forms primarily in plutonic rocks like granite or pegmatites as magma cools slowly deep underground. This specific specimen appears water-worn (river rock), suggesting it was eroded from its source and tumbled in water over long geological periods.

Uses & Applications

Used in the manufacture of glass and ceramics (porcelain), as a mild abrasive in scouring powders, and occasionally as a gemstone (if high quality like Moonstone).

Geological Facts

Feldspar is the most abundant mineral group in the Earth's crust, making up about 60% of terrestrial rocks. The pink color is often due to trace amounts of hematite or iron within the crystal lattice.

Field Identification & Locations

Identify in the field by its distinct salmon-pink color, blocky cleavage planes, and hardness (it will scratch glass but cannot be scratched by a steel knife). Commonly found in mountain ranges or riverbeds near granitic outcrops.

Identified on: 4/27/2026

Mode: Standard