Glaucophane schist also known as Blueschist is a metavolcanic rock that forms by the metamorphism of basalt and rocks with similar composition at high pressures and low temperatures, approximately corresponding to a depth of 15 to 30 kilometers and 200 to ~500 degrees Celsius. The blue color of the rock comes from the presence of the predominant minerals glaucophane and lawsonite. Usually fine grained due to the rapidity & low temperatures of the mechanism involved. However, porphyritic varieties can be found. This example is from the Isle of Anglesey, N. Wales. Specimens are supplied in labelled card trays.