The tetravalent manganese oxides: identification, hydration, and structural relationships by infrared spectroscopy

A compilation of the infrared powder absorption spectra of most naturally occurring tetravalent and trivalent manganese oxides is presented which is intended to serve as a basis for the spectroscopic identification of these minerals in both ordered and disordered varieties, including those too disordered for X-ray diffraction studies. A variety of synthetic manganese oxides are also included for comparison to the natural phases. The samples include: aurorite, birnessite, braunite, buserite, chalcophanite, coronadite, cryptomelane, groutite, hausmannite, hollandite, lithiophorite, maoganite, manganese(Ill) manganate(IV), manganosite, manjiroite, marokite, nsutite, partridgeite, pyrolusite, quenselite, rancieite, ramsdellite, romanechite, sodium manganese(Il,III) manganate(IV), todorokite, and woodruffite. The spectra indicate that well-ordered water occurs in ramsdellite, chalcophanite, and most romanechites. Disordered water is observed in the spectra of nsutite, hollandites, birnessite, todorokite, buserite, and rancieite. The infrared spectra of well-ordered todorokite, birnessite and rancieite differ which indicates that they possess different structures and should be regarded as distinct mineral species. Much variation is observed in the spectra of pyrolusites, nsutites, birnessites, and todorokites which is interpreted as arising from structural disorder. Spectral trends suggest that todorokite, birnessite and rancieite have layered structures.