Schist is medium grade metamorphic rock, formed by the metamorphosis of mudstone / shale, or some types of igneous rock, to a higher degree than slate, i.e. it has been subjected to higher temperatures and pressures. The resulting folia- tion is coarser and more distinct than that of slate due to the higher degree of crystallisation of mica minerals forming larger crystals, and is often referred to as schistosity. These larger crystals reflect light so that schist often has a high lustre, i.e. it is shiny., 2016
