mineral

Feldspar (Orthoclase)

Orthoclase Feldspar (KAlSi3O8)

Hardness: 6 on Mohs scale; Color: Off-white, cream, or pinkish; 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: Off-white, cream, or pinkish
Luster: Vitreous to pearly

Identified April 10, 2026More mineral →

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Physical properties

Hardness: 6 on Mohs scale; Color: Off-white, cream, or pinkish; Luster: Vitreous to pearly; Crystal Structure: Monoclinic; Cleavage: Two planes meeting at 90 degrees; Specific Gravity: 2.55-2.63

Formation & geological history

Formed in igneous rocks like granite and pegmatites through the cooling of magma. It is one of the most abundant minerals in the Earth's crust, found in mountain ranges worldwide.

Uses & applications

Used in the manufacture of glass and ceramics, as a filler in paints and plastics, and occasionally as a gemstone (such as moonstone).

Geological facts

Orthoclase is a defining mineral for level 6 on the Mohs scale of mineral hardness. The name 'orthoclase' comes from the 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 blocky cleavage, vitreous luster, and its inability to be scratched by a steel knife (which is usually around 5.5). Commonly found in granite outcrops.

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