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Anorthite is one of the plagioclase feldspars, an important group of minerals abundant in the Earth's crust. Anorthite's chemical formula is CaAl2Si2O8.

Table of contents
1 Mineralogy
2 Occurrence
3 Details
4 See also
5 External link


Anorthite is the calcium-rich endmember of the plagioclase system, the other endmember being albite (sodium-rich). The range of intermediate compositions have varying ratios of calcium and sodium ions.


Anorthite occurs in igneous and metamorphic rocks. Its type localities are Monte Somma and Valle di Fassa, Italy,


Crystallographic systemTriclinic
ColoursNormally colourless or white, colourless in thin section.
Refractive index 1.51
Cleavage3: 1 perfect, 1 good, 1 poor
TwinningMultiple lamellar and Carlsbad twins
PleochroismYellow to dark green to transparent to opaque

See also

External link