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Plagioclase feldspars form a continuous series of tectosilicates (framework
silicates) from
anorthite to albite. They include
albite variety oligoclase (10% to 30% anorthite),
albite variety andesine (30% to 50% anorthite),
anorthite variety labradorite (50% to 70% anorthite) and
anorthite variety 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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