Anorthite
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| Anorthite | |
 Anorthite from Japan |
|
| General | |
|---|---|
| Category | Feldspar mineral |
| Chemical formula | CaAl2Si2O8 |
| Identification | |
| Color | White, grayish, reddish |
| Crystal habit | Anhedral to subhedral granular |
| Crystal system | Triclinic |
| Twinning | Common |
| Cleavage | Perfect [001] good [010] |
| Fracture | Uneven to concoidal |
| Tenacity | Brittle |
| Mohs Scale hardness | 6 |
| Luster | Vitreous |
| Diaphaneity | Transparent to translucent |
| Specific gravity | 2.72 - 2.75 |
| Optical properties | Biaxial (-), 2V 78° to 83° |
| Refractive index | nα = 1.573 - 1.577 nβ = 1.580 - 1.585 nγ = 1.585 - 1.590 |
| Birefringence | δ = 0.012 - 0.013 |
| References | [1][2][3] |
Anorthite is a compositional variety of plagioclase feldspar. Plagioclase is an abundant mineral in the Earth's crust. The formula of pure anorthite is CaAl2Si2O8.
Contents |
[edit] Mineralogy
Anorthite is the calcium-rich endmember of the plagioclase solid solution series, the other endmember being albite, NaAlSi3O8. Anorthite also refers to plagioclase compositions with more than 90 molecular percent of the anorthite endmember.
[edit] Occurrence
Anorthite is a rare compositional variety of plagioclase. It occurs in mafic igneous rock. It also occurs in granulite facies metamorphic rocks, in metamorphosed carbonate rocks and corundum deposits.[1] Its type localities are Monte Somma and Valle di Fassa, Italy. It was first described in 1823.[3]
It also makes up much of the lunar highlands. 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.
[edit] See also
[edit] References
- ^ a b http://www.handbookofmineralogy.org/pdfs/anorthite.pdf Handbook of Mineralogy
- ^ http://www.mindat.org/min-246.html Mindat
- ^ a b http://webmineral.com/data/Anorthite.shtml Webmineral
