Biotite is a name used for a large group of black mica minerals that are commonly found in igneous and metamorphic rocks. These include annite, phlogopite, siderophyllite, fluorophlogopite, fluorannite, eastonite, and many others. The name "biotite" is used because these minerals generally cannot be distinguished without optical, chemical, or x-ray analysis. Biotite was named in honor of the French physicist Jean-Baptiste Biot, who performed early research into the many optical properties of mica.