- a gray to black mineral, hydrous manganese oxide, MnO(OH); gray manganese ore.
- any of a series of salts containing tetravalent manganese and derived from either of two acids, H4MnO4 or H2MnO3.
- a blackish mineral consisting of basic manganese oxide in monoclinic crystalline form: a source of manganese. Formula: MnO(OH)
