Iyoite is a very rare manganese copper chloride hydroxide mineral with the formula MnCuCl(OH)<sub>3</sub>. Iyoite is a new member of the atacamite group, and it an analogue of botallackite characterized in manganese and copper ordering. Iyoite is monoclinic (space group P2<sub>1</sub>/m). It is chemically similar to misakiite. Both minerals come from the Ohku mine in the Ehime prefecture, Japan.