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Anorthite

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

Mineralogy 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.

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

Details

Crystallographic systemTriclinic
ColoursNormally colourless or white, colourless in thin section.
LustreVitreous
Hardness6-6.5
Refractive index 1.51
Cleavage3: 1 perfect, 1 good, 1 poor
TwinningMultiple lamellar and Carlsbad twins[?]
PleochroismYellow to dark green to transparent to opaque

 

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