CHARACTERISTICS OF MANGANITE (GAMMA-MNOOH) IN MANGANESE-RICH GANGPUR GROUP OF ROCKS, ORISSA

Manganite gamma-MnOOH, in the manganese-rich rocks of Precambrian Gang pur Group, Sundargarh district, Orissa, shows dissimilar fabrics and b elongs to three generations but has more or less similar chemical comp osition. It occurs as patchy inclusions, accicular crystallites, egg-s haped micro-nodules, medium to coarse-grained mosaics, vein and fissur e fillings and as wedge-shaped linings. The manganite is either formed from Mn-oxide (jacobsite and vredenburgite) phases through retrogress ive metamorphic transformation (Ma1) or generated through pseudomorphi c replacement of Mn-sillicate (rhodonite and tephroite) or Mn-carbonat e (rhodochrosite) by chemical weathering under supergene conditions (M a2). The vein filling type is the latest in its paragenesis (Ma3). Des pite different mineral lineages, manganites are chemically similar tho ugh crystallites located in veins and fissures are relatively pure.