Gmelin Handbook of Inorganic and Organometallic Chemistry

Described are manganese minerals of the hollandite group of MO2-type Mn tunnel oxides. The tunnel sites in these structures are occupied mainly by Ba2+ in hollandite, by K+ in cryptomelane, by Na++ in manjiroite, and by Pb2+ in coronadite. All hollandite-group Mn oxides are typically formed at low-temperature conditions. Only hollandite is about equally abundant as a low- and high-temperature phase which distinguishes it from the other members of the group. Since the hollandite-group oxides often contain K as a tunnel cation, they can be used for dating ore emplacement as well as weathering processes by the K - Ar and 40Ar - 39Ar methods.