Abstract
Hydration of orthopyroxene (En 60) in contact with plagioclase (An 36) leads to oronas of the type orthopyroxene-cummingtonite-edenite + quartz-edenitic hornblende. The compositions of the minerals involved indicate that kyanite needles in the adjacent plagioclases form as part of the reaction: orthopyroxene (En 60) + plagioclase (An 36) + H 2O→ cummingtonite + edenite/edenitic hornblende + plagioclase (< An 36) + kyanite + quartz. The reaction proceedings consumption first of the orthopyroxene and later of the cummingtonite to produce a corona structure consisting of a core of intergrown edenite and quartz surrounded by edenitic hornblende. Corona evolution of this type is controlled by diffusion.
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