Blueschist facies

Blueschist (pronunciation: /ˈbluːʃɪst/), also called glaucophane schist, is a metavolcanic rock that forms by the metamorphism of basalt and rocks with similar composition at high pressures and low temperatures (200 to ~500 degrees Celsius), approximately corresponding to a depth of 15 to 30 kilometers. The blue color of the rock comes from the presence of the predominant minerals glaucophane and lawsonite.

Blueschists are typically found within orogenic belts as terranes of lithology in faulted contact with greenschist or rarely eclogite facies rocks.

Blueschist, as a rock type, is defined by the presence of the minerals glaucophane + ( lawsonite or epidote ) +/- jadeite +/- albite or chlorite +/- garnet +/- muscovite in a rock of roughly basaltic composition.
Blueschist often has a lepidoblastic, nematoblastic or schistose rock microstructure defined primarily by chlorite, phengitic white mica, glaucophane, and other minerals with an elongate or platy shape.

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