Plagioclase

tectosilicate

anorthite

Plagioclase feldspars form a continuous series of tectosilicates (framework silicates) from
anorthite CaAl2Si2O8 to
albite NaAlSi3O8. They include oligoclase (10 to 30% anorthite), andesine (30 to 50% anorthite), labradorite (50 to 70% anorthite) and bytownite (70 to 90% anorthite), as well as the end members.
Environments:

Plutonic igneous environments
Volcanic igneous environments
Metamorphic environments

The plagioclase feldspars are widely distributed as rock-forming minerals, and more abundant than the K-feldspars. They are minerals of the granulite facies. Plagioclase is an essential constituent of diorite, rhyolite, andesite and basalt.
It is a common constituent of quartzolite and also may be found in granite.
It is a mineral of the hornblende-hornfels, pyroxene-hornfels, amphibolite and granulite facies.

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