anorthite

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.
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Noun
1. rare plagioclastic feldspar occurring in many igneous rocks
(hypernym) plagioclase, oligoclase

n. anorthite

(n.)
A mineral of the feldspar family, commonly occurring in small glassy crystals, also a constituent of some igneous rocks. It is a lime feldspar. See Feldspar.
  

General Information:
 Chemical Formula:
CaAl2Si2O8
 Composition:
(Molecular Weight = 277.41 gm)
Sodium 0.41 % Na
Calcium 13.72 % Ca
Aluminum 18.97 % Al
Silicon 20.75 % Si
Oxygen 46.14 % O 
 Empirical Formula:
Na0.05Ca0.95Al1.95Si2.05O8
 Environment:
Magmatic and metamorphic rocks.
 Locality:
Monte Somma and Valle di Fassa, Italy.
 Name Origin:
From the Greek, an + orthos, "not upright" in allusion to the oblique crystals.
Physical Properties:
 Cleavage:
[001] Perfect, [010] Good
 Color:
colorless, gray, white, red, or reddish gray.
 Density:
2.72 - 2.75, Average = 2.73
 Diaphaniety:
Transparent to Subtransparent to translucent
 Habits:
Granular - Generally occurs as anhedral to subhedral crystals in matrix., Euhedral Crystals - Occurs as well-formed crystals showing good external form., Striated - Parallel lines on crystal surface or cleavage face.
 Hardness:
6 - Orthoclase
 Luminescence:
None.
 Luster:
Vitreous (Glassy)
 Streak:
white
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