Manganese oxide tunnel structures and their intergrowths.

Natural hollandite and romanechite are widespread barium-containing manganese minerals. High-resolution transmission electron microscopy indicates that intergrowths of the two minerals occur in a coherent manner on the unit-cell level with no apparent ordering of the hollandite and romanechite. Other structures have been imaged that are based on the hollandite and romanechite structures. Electron microscopy holds a key to unraveling the myriad structural complexities of the manganese oxides.