mineral

Orthoclase Feldspar

Potassium aluminum silicate (KAlSi3O8)

Hardness: 6 on Mohs scale; Color: typically salmon pink to reddish-orange; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Two planes at right angles (90 degrees); Specific gravity: 2.55-2.63.

Hardness: 6 on Mohs scale
Color: typically salmon pink to reddish-orange
Luster: Vitreous to pearly

Identified March 21, 2026More mineral →

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Physical properties

Formation & geological history

Formed through the crystallization of magma in intrusive igneous rocks such as granite and syenite; also common in metamorphic rocks like gneiss. This specimen is typically found in environments ranging from Precambrian to Cenozoic eras.

Uses & applications

Used primarily in the manufacture of glass and ceramics (porcelain); sometimes used as a semi-precious gemstone (Moonstone variation) or as a decorative aggregate in landscape design.

Geological facts

Orthoclase is one of the most common minerals in the Earth's crust. It is a defining mineral for level 6 on the Mohs hardness scale, making it a standard for geological comparison.

Field identification & locations

Identify in the field by its distinctive 'salmon' pink color and its two sets of cleavage planes that meet at near-perfect 90-degree angles. It will scratch glass but cannot be scratched by a steel nail. Commonly found in mountainous granite outcrops and riverbeds.

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