Vitriol is the general chemical name encompassing a class of chemical compound comprising sulfates of certain metals – originally, iron or copper. Those mineral substances were distinguished by their color, such as green vitriol for hydrated iron(II) sulfate and blue vitriol for hydrated copper(II) sulfate.

These materials were originally found as crystals formed by evaporation of groundwater that percolated through sulfide minerals and collected in pools on the floor of old mines. The word vitriol comes from the Latin word vitriolus, meaning "small glass", as those crystals resembled pieces of colored glass.

Oil of vitriol was an old name for concentrated sulfuric acid, which was historically obtained through the dry distillation (pyrolysis) of vitriols. The name, shortened to vitriol, continued to be used for this viscous liquid long after the minerals came to be called "sulfates". The term vitriolic in the sense of "harshly condemnatory" is derived from the corrosive nature of this substance.