D.R. Khullar holds that mining in India depends on over 3,100 mines, out of which over 550 are fuel mines, over 560 are mines for metals, and over 1970 are mines for extraction of nonmetals. The figure given by S.N. Padhi is: 'about 600 coal mines, 35 oil projects and 6,000 metalliferous mines of different sizes employing over one million persons on a daily average basis.' Both open cast mining and underground mining operations are carried out and drilling/pumping is undertaken for extracting liquid or gaseous fuels. The country produces and works with roughly 100 minerals, which are an important source for earning foreign exchange as well as satisfying domestic needs. India also exports iron ore, titanium, manganese, bauxite, granite, and imports cobalt, mercury, graphite etc.