• hollandite
• thermal behavior

Since their technological importance and their abundance, a series of studies on a number of tunnel oxide minerals has been undertaken and discussed in this thesis, aiming at better understanding their properties.
Several X-ray diffraction experiments at ambient and non-ambient conditions will be shown, with special attention to the cation distribution within the tunnels and the thermal behavior of these minerals. A series of experiments carried out to identify the presence of water molecules within the tunnels will be described.
Besides, the revision of the nomenclature of a specific group of minerals with tunnel structures (hollandite supergroup, the major subject of this work) will be presented