Anorthite
A variety of Minerals
What is Anorthite?
Anorthite is the calcium endmember of the plagioclase feldspar mineral series. The chemical formula of pure anorthite is CaAl2Si2O8. Anorthite is found in mafic igneous rocks. Anorthite is rare on the Earth but abundant on the Moon.
Optical Properties
- Refractive Index
- 1.575-1.588
- Birefringence
- 0.013
- Optical Character
- Biaxial negative
Market Value Factors
Pricing varies for every rock and mineral, so use these universal factors to gauge Anorthite 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.
Anorthite Localities Map
See where Anorthite is found with a localities map, collecting zones, and geology context. Generate a sample map preview below.
Key Characteristics
Formation of Anorthite
Anorthite is a rare compositional variety of plagioclase. It occurs in mafic igneous rock. It also occurs in metamorphic rocks of granulite facies, in metamorphosed carbonate rocks, and corundum deposits. Its type localities are Monte Somma and Valle di Fassa, Italy. It was first described in 1823. It is more rare in surficial rocks than it normally would be due to its high weathering potential in the Goldich dissolution series. It also makes up much of the lunar highlands; the Genesis Rock is made of anorthosite, which is composed largely of anorthite. Anorthite was discovered in samples from comet Wild 2, and the mineral is an important constituent of Ca-Al-rich inclusions in rare varieties of chondritic meteorites.
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Quick Facts
Physical Properties
- Color
- Colourless, reddish grey, white
- Hardness (Mohs)
- 6 - 6.5
- Density
- 2.76 g/cm³
- Streak
- White
Chemical Properties
- Chemical Formula
- Ca(Al2Si2O8)
- Elements
- Al, Ca, O, Si
Also Known As
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Anorthite FAQs
How do I identify Anorthite?
Anorthite can be identified by its hardness of 6 - 6.5 on the Mohs scale, Colourless color. Look for these key characteristics when examining specimens.
What color is Anorthite?
Anorthite typically appears in Colourless, reddish grey, white. Color can vary depending on impurities and formation conditions.
How hard is Anorthite?
Anorthite has a hardness of 6 - 6.5 on the Mohs scale. This gives it moderate hardness.
What is the formation of anorthite of Anorthite?
Anorthite is a rare compositional variety of plagioclase. It occurs in mafic igneous rock. It also occurs in metamorphic rocks of granulite facies, in metamorphosed carbonate rocks, and corundum deposits. Its type localities are Monte Somma and Valle di Fassa, Italy. It was first described in 1823. It is more rare in surficial rocks than it normally would be due to its high weathering potential in the Goldich dissolution series. It also makes up much of the lunar highlands; the Genesis Rock is made of anorthosite, which is composed largely of anorthite. Anorthite was discovered in samples from comet Wild 2, and the mineral is an important constituent of Ca-Al-rich inclusions in rare varieties of chondritic meteorites.
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