Blueschist ( /ˈbluːˌʃɪst/), 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 (200–500 °C (392–932 °F)), approximately corresponding to a depth of 15–30 km (9.3–18.6 mi).

Where do schists form?

It usually forms on a continental side of a convergent plate boundary where sedimentary rocks, such as shales and mudstones, have been subjected to compressive forces, heat, and chemical activity.

Is Glaucophane a metamorphic?

Glaucophane is a metamorphic mineral, obviously characteristic of, but non strictly restricted to the glaucophane schist facies (blueschist facies), wich, in turn, implies low temperature, high pressure metamorphism. Optical properties: Form: Acicular to columnar crystals.