Hollandite and cryptomelane in the manganese oxide deposits of the Sausar Group, India

The phase chemistry and the structure of hollandite-cryptomelane series in the Precambrian Sausar Group of India are reinvestigated. The tunnel-cations of the hollandite-cryptomelane series of the present investigation do not show complete exchanges. Crystal symmetry of these minerals is affected by the amounts and the composition of the tunnel cations. With increasing Ba2+ content, symmetry of cryptomelane in Tirodi area changes from tetragonal to monoclinic. These minerals appear to have been formed in a wide range of metamorphic grade from the lowest (chlorite-biotite) to the highest (sillimanite) grades. The local breakdown of hollandite to hausmannite ± Ba-feldspar must have occurred by the change of fO2 condition of the system during metamorphism