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.
Reference: Ernst, W. G. (1973). “Blueschist Metamorphism and P-T Paths in Subduction Zones.” American Journal of Science, 273(6), 577-606.