mineral
Orthoclase Feldspar
KAlSi3O8 (Potassium Aluminum Silicate)
Hardness: 6 (Mohs); Color: Salmon-pink, tan, or white; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Two planes meeting at nearly 90 degrees; Specific gravity: 2.55-2.63
- Hardness
- 6 (Mohs)
- Color
- Salmon-pink, tan, or white
- Luster
- Vitreous to pearly
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Physical properties
Hardness: 6 (Mohs); Color: Salmon-pink, tan, or white; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Two planes meeting at nearly 90 degrees; Specific gravity: 2.55-2.63
Formation & geological history
Formed in igneous environments like granite or pegmatite, as well as in some metamorphic rocks. Most specimens are hundreds of millions of years old, often from the Precambrian or Paleozoic eras.
Uses & applications
Used in the manufacturing of glass and ceramics (as a flux), porcelain, and occasionally used as a gemstone (Moonstone is a variety). Collectors value well-defined cleavage planes.
Geological facts
Orthoclase is one of the ten index minerals in the Mohs hardness scale. The name 'orthoclase' is Greek for 'straight fracture,' referring to its two cleavage planes at right angles.
Field identification & locations
Identify in the field by its distinct salmon-pink color, blocky shape, and two right-angle cleavage planes. It is a major constituent of granite, frequently found in mountainous regions.
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metamorphic
Gypsum (variety Selenite or Alabaster)
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Mineral
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Nephrite
Mineral/Rock
Banded Gneiss (River Rock/Pebble)
Gneiss (specifically a banded variety often found as a river rock)
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