Blueschist is a type of metamorphic rock that forms under high-pressure, low-temperature conditions typically found in subduction zones. It is characterized by the presence of blue-colored amphibole minerals such as glaucophane. Blueschist facies rocks are important in the study of tectonics and metamorphism, providing insights into the conditions and processes in subduction environments.
Source Ernst, W. G. (1973). “Blueschist Metamorphism and P-T Paths in Subduction Zones.” American Journal of Science, 273(6), 577-606.