What is "whiteschist"

A whiteschist is an uncommon metamorphic rock formed at high to ultra-high pressures. It has the characteristic mineral assemblage of kyanite + talc, responsible for its white colour. The name was introduced in 1973 by German mineralogist and petrologist Werner Schreyer. This rock is associated with the metamorphism of some pelites, evaporite sequences or altered basaltic or felsic intrusions. Whiteschists form in the MgO–––– (MFASH) system. Rocks of this primary chemistry are extremely uncommon and they are in most cases thought to be the result of metasomatic alteration, with the removal of various mobile elements.