Schists are metamorphic rocks that are composed of a variety of mineral including quartz, mica, feldspar, hornblende, chlorite, graphite, and talc. These are in the form of thin flakes that can be easily seperated from each other — indeed the name "schist" is from the Greek term for "split". Most are derived from sedimentary materials like clay or mud that has then undergone a series of metamorphic processes. Others started out as igneous rocks such as basalt; however, it can be very difficult, if not impossible, to determine the exact provenance of those examples that have undergone significant metamorphic change.