A SHORT OUTLINE OF THE TUNNEL OXIDES

Abstract

Within the large and comprehensive group of oxide minerals, the most relevant subgroup in the frame of microporous materials is that of the so-called “tunnel oxides.” This rather generic term historically refers to a number of minerals which, from a chemical point of view, are (mainly) manganese oxides. In nature manganese occurs in three different oxidation states—Mn2+, Mn3+ and Mn4+—with the latter being the dominant form in tunnel oxides.