Orthoclase
A variety of Alkali Feldspar
What is Orthoclase?
Orthoclase is a feldspar mineral and one of the most common rock-forming materials in Earth's crust. It is usually encountered within different types of granite, where it is responsible for the pinkish or lighter flecks in that rock. The iridescent gemstone known as moonstone is also a variant of orthoclase.
Uses & Applications
Orthoclase is commonly used as a raw material for manufacturing certain types of glass and porcelain. It is also a constituent of scouring powder. The intergrowths of orthoclase are called Moonstones when used in jewelry making and are known for their attractive sheen (adularescence).
Healing Properties
Orthoclase is an excellent stone for believers who need emotional healing and the restoration of hope and enthusiasm for life. It can be used to align all of the chakras, but is mainly linked to the Solar Plexus chakra. It aims to restore vitality and is often used to enhance exercise and encourage proper breathing patterns.
Optical Properties
- Refractive Index
- 1.518-1.536
- Birefringence
- 0.005-0.008
- Pleochroism
- Weak
- Optical Character
- Biaxial negative
- Dispersion
- 0.012
Market Value Factors
Pricing varies for every rock and mineral, so use these universal factors to gauge Orthoclase before comparing listings or appraisals.
Size & Weight
Larger, intact specimens usually command higher prices.
Rarity & Demand
Scarce material or popular varieties sell at a premium.
Condition & Finish
Chips, repairs, and heavy wear lower value; clean prep helps.
Treatment & Provenance
Untreated specimens with documented locality are prized.
Orthoclase Localities Map
See where Orthoclase is found with a localities map, collecting zones, and geology context. Generate a sample map preview below.
The Meaning
Orthoclase is the official state gem of Florida (USA).
Associated Chakras
Key Characteristics
Formation of Orthoclase
Orthoclase is a common constituent of most granites and other felsic igneous rocks and often forms huge crystals and masses in pegmatite. Typically, the pure potassium endmember of orthoclase forms a solid solution with albite, the sodium endmember (NaAlSi3O8), of plagioclase. While slowly cooling within the earth, sodium-rich albite lamellae form by exsolution, enriching the remaining orthoclase with potassium. The resulting intergrowth of the two feldspars is called perthite. The higher-temperature polymorph of KAlSi3O8 is sanidine. Sanidine is common in rapidly cooled volcanic rocks such as obsidian and felsic pyroclastic rocks, and is notably found in trachytes of the Drachenfels, Germany. The lower-temperature polymorph of KAlSi3O8 is microcline. Adularia is a low temperature form of either microcline or orthoclase originally reported from the low temperature hydrothermal deposits in the Adula Alps of Switzerland. It was first described by Ermenegildo Pini in 1781. The optical effect of adularescence in moonstone is typically due to adularia. The largest documented single crystal of orthoclase was found in the Ural mountains in Russia. It measured ~10×10×0.4 m and weighed ~100 tons.
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Quick Facts
Physical Properties
- Color
- Colorless to white, Greenish white, Grayish yellow, Pale pink
- Hardness (Mohs)
- 6
- Density
- 2.563 g/cm³
- Streak
- White
- Luster
- Vitreous, Resinous
- Crystal System
- Monoclinic
Chemical Properties
- Chemical Formula
- K(AlSi3O8)
- Elements
- Al, K, O, Si
Also Known As
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Orthoclase FAQs
How do I identify Orthoclase?
Orthoclase can be identified by its hardness of 6 on the Mohs scale, Colorless to white color, Vitreous, Resinous luster, Monoclinic crystal system. Look for these key characteristics when examining specimens.
What color is Orthoclase?
Orthoclase typically appears in Colorless to white, Greenish white, Grayish yellow, Pale pink. Color can vary depending on impurities and formation conditions.
How hard is Orthoclase?
Orthoclase has a hardness of 6 on the Mohs scale. This gives it moderate hardness.
What is the formation of orthoclase of Orthoclase?
Orthoclase is a common constituent of most granites and other felsic igneous rocks and often forms huge crystals and masses in pegmatite. Typically, the pure potassium endmember of orthoclase forms a solid solution with albite, the sodium endmember (NaAlSi3O8), of plagioclase. While slowly cooling within the earth, sodium-rich albite lamellae form by exsolution, enriching the remaining orthoclase with potassium. The resulting intergrowth of the two feldspars is called perthite. The higher-temperature polymorph of KAlSi3O8 is sanidine. Sanidine is common in rapidly cooled volcanic rocks such as obsidian and felsic pyroclastic rocks, and is notably found in trachytes of the Drachenfels, Germany. The lower-temperature polymorph of KAlSi3O8 is microcline. Adularia is a low temperature form of either microcline or orthoclase originally reported from the low temperature hydrothermal deposits in the Adula Alps of Switzerland. It was first described by Ermenegildo Pini in 1781. The optical effect of adularescence in moonstone is typically due to adularia. The largest documented single crystal of orthoclase was found in the Ural mountains in Russia. It measured ~10×10×0.4 m and weighed ~100 tons.
