1. The Archaean Group

Ancient crystalline and highly metamorphosed gneisses of the Archaean System are found in the plateaus of Tamil Nadu, Nilgiris, Karnataka, Andhra Pradesh, Maharashtra, Chhotanagpur, West Bengal, Odisha,Jharkhand, Chhattisgarh, Madhya Pradesh, Meghalaya, Mikir, Bundelkhand (U.P.) and the Aravallis (Rajasthan). The Bengal gneiss known as Khondolite is found in the Eastern Ghats. These rocks are rich in metallic and non-metallic minerals, precious stones and building materials.