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These are the massive, eruptive dark coloured gneiss. The name being given in honour of Job Charnock whose tombstone in Kolkata was made of this rock. The Nilgiri gneiss is bluish-grey to dark coloured rock, medium to coarse grained in texture. This is plutonic gneiss intruding into the other Archaean rock masses. Nilgiri gneiss is popularly recognised as belonging to the Charnockite series. Itiswidely found in South Ar cot, Palni Hills, Shevaroy Hills and Nilgiri in Tamil Nadu, Nellore in Andhra Pradesh, Balasore in Odisha, Karnataka, Kerala, Malabar, J hark hand, Chhattisgarh and Aravallis (Rajasthan).
The Archaean rocks are the repositories of the mineral wealth of India. These rocks are rich in ferrous and non-ferrous minerals like iron ore, copper, manganese, mica, dolomite, lead, zinc, silver and gold.