Schist is a medium-grade metamorphic rock characterized by a pronounced foliation called schistosity, which results from the alignment of platy or elongated mineral grains such as mica, chlorite, talc, biotite, muscovite, and sometimes amphiboles like hornblende. These minerals are large enough to be visible to the naked eye, allowing the rock to be easily split into thin flakes or slabs along the foliation planes
. Schist typically forms through regional metamorphism, often associated with mountain-building processes, from precursor rocks like mudstones, shales, or some igneous rocks. The metamorphic conditions involve higher temperatures and pressures than those forming slate, leading to coarser foliation and larger mica crystals that give schist its characteristic shiny appearance
. There are many varieties of schist named after their dominant minerals, such as mica schist, garnet schist, chlorite-rich green schist, and others. Schist often contains porphyroblasts-large crystals of minerals like garnet or staurolite-that grew during metamorphism
. In summary, schist is a foliated metamorphic rock rich in platy minerals, formed under medium-grade metamorphic conditions, and recognizable by its shiny, layered texture and ability to split easily along parallel mineral grains.
