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

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 system	Triclinic
Colours	Normally colourless or white, colourless in thin section.
Lustre	Vitreous
Hardness	6-6.5
Refractive index	1.51
Cleavage	3: 1 perfect, 1 good, 1 poor
Twinning	Multiple lamellar and Carlsbad twins[?]
Pleochroism	Yellow to dark green to transparent to opaque

See also

• Feldspars
• List of minerals

External link

• WebMineral entry (http://webmineral.com/data/Anorthite.shtml)