mineral
Orthoclase Feldspar
KAlSi3O8 (Potassium aluminum silicate)
Hardness: 6 on Mohs scale; Color: Tan, peach, or off-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
- Tan, peach, or off-white
- Luster
- Vitreous to pearly
Identified More mineral →
Explore Orthoclase Feldspar in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6 on Mohs scale; Color: Tan, peach, or off-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 igneous rocks like granite and syenite through the cooling of magma, and in metamorphic rocks like gneiss. Found in environments spanning from the Precambrian to recent eras.
Uses & applications
Used in the manufacture of glass and ceramics (porcelain), as a filler in paints and plastics, and occasionally as a gemstone (moonstone variety).
Geological facts
Orthoclase is one of the ten defining minerals of the Mohs scale of mineral hardness. The name is derived from the Greek words for 'straight fracture,' referring to its two cleavage planes at right angles.
Field identification & locations
Identify by its blocky appearance and prominent 90-degree cleavage planes. Commonly found in granitic pegmatites worldwide, such as in the Appalachian Mountains or the Alps.
More like this
Other mineral specimens
Sandstone (with potential mineral staining/concretions)
Arenite (SiO2 based)
sedimentary
Schist
Schist
Metamorphic
Epidote
Epidote | Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH)
metamorphic
Gypsum (variety Selenite or Alabaster)
Calcium sulfate dihydrate (CaSO4·2H2O)
Mineral
Nephrite Jade
Nephrite
Mineral/Rock
Granite
Granite (Phaneritic intrusive igneous rock)
igneous