BiotiteBiotite is a member of the mica group of silicates (sheet silicates), like chlorite and muscovite. It occurs in more geological environments than any of the other micas. It is a common rock forming mineral, being present in at least some percentage in many igneous rocks (e.g. granite and rhyolite), and metamorphic rocks (e.g. schist, gneiss).
Chemical composition - K(Fe, Mg)