In India the highest concentration of manganese is found in the Dharwar system of rocks. The richly manganiferous faces of this system-the Gondi and Obdurate series contain enormous aggregates of manganese ores such as psilomelane, braunite, pyrolusite, hollandite, etc. Of these the first two form nearly 90 per cent of the ore masses.
These mainly belong to the syngenetic type of ore bodies, i.e. those which were formed contemporaneously with the enclosing rock, while the last belong to the epigenetic class of ores, i.e., those formed by a process of concentration at a later date. Manganese deposits are connected with the intrusive rock, Kodurite (a basic plutonic rock); elastic sediments of the Gondite rocks; and lateritic deposits due to metasomatic surface replacement of Dharwar slates and schists.
Psilomelane (Mn2Oj, BaO, H20) and braunite (Mn203) ores account for over 90 per cent of the total reserves of manganese in the country. Pyrolusite (Mn02) and cryptomelane are other important ores.
Manganese ores are termed differently depending upon the percentage of manganese content. Ores with 40 to 60 per cent of manganese are classed as manganese ore; with 10 to 30 per cent of iron (and 10 to 40 per cent of manganese) as ferruginous manganese; with iron 40 per cent and manganese from 5 to 10 per cent as manganiferous iron; and iron more than 50 per cent but manganese less than 5 per cent as iron ore.