Characteristics of Manganite (γ-MnOOH) in Manganese-Rich Gangpur Group of Rocks, Orissa

Manganite γ-MnOOH, in the manganese-rich rocks of Precambrian Gangpur Group, Sundargarh district, Orissa, shows dissimilar fabrics and belongs to three generations but has more or less similar chemical composition. It occurs as patchy inclusions, accicular crystallites, egg-shaped micro-nodules, medium to coarse-grained mosaics, vein and fissure fillings and as wedge-shaped linings. The manganite is either formed froin Mn-oxide (jacobsite and vredenburgite) phases through retrogressive metamorphic transformation (Ma1) or generated through pseudomorphic replacement of Mn-sillicate (rhodonite and tcphroite) or Mn-carbonate (rhodochrosite) by chemical weathering under supergene conditions (Ma2). The vein filling type is the latest in its paragenesis (Ma3). Despite different mineral lineages, manganites are chemically similar though crystallites located in veins and fissures are relatively pure.