blueschist
[blōō′shĭst′]
A bluish schist that gets its color from the presence of a sodic amphibolite, glaucophane, or a variety of glaucophane called crossite. Blueschist forms under conditions of high pressure but low temperature, as at the boundaries of converging tectonic plates.
The American Heritage® Science Dictionary
Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.