mineral

Orthoclase Feldspar

Orthoclase (KAlSi₃O₈)

Hardness: 6 on Mohs scale; Color: typically salmon-pink, flesh-red, or creamy white; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Two directions at 90 degrees; Specific gravity: 2.55–2.63.

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

Identified March 11, 2026More mineral →

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Physical properties

Formation & geological history

Formed as a primary constituent of granitic igneous rocks (plutonic) through the cooling of silica-rich magma; also found in metamorphic rocks like gneiss. It is one of the most common minerals in the Earth's crust.

Uses & applications

Used extensively in the manufacture of glass and ceramics (porcelain); used as a mild abrasive in scouring powders; high-quality transparent varieties are sometimes cut as gemstones (Moonstone).

Geological facts

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

Field identification & locations

Identify in the field by its distinct salmon-pink color and the way it reflects light off its flat cleavage planes. It is commonly found in gravel, gardens, and mountainous granite outcrops globally. Look for it alongside quartz and mica.