KOLKATA: Is there a diamond field that runs in a wide swathe under the earth’s crust across Andhra Pradesh and Tamil Nadu ? There may well be, according to new research by geologists Subrata Das Sharma and Durbha Sai Ramesh of the National Geophysical Research Institute (NGRE) in Hyderabad.They have suggested that a vast area in southeast India — 200,000 sq km — could contain diamond-bearing rocks in a report published in the August issue of Lithosphere, the peer-reviewed journal of the Geological Society of America.While all this is very preliminary in nature, the findings could potentially bring cheer to the country’s diamond traders and exporters who otherwise have to depend on supplies of rough stones from Botswana, Namibia, South Africa , Russia, Canada and Australia.India, which has an Rs 80,000-crore diamond industry, is the world’s biggest hub for the polishing of rough stones. Local availability will automatically lower the cost of production and increase the margins of diamond traders, many of whom say these have shrunk as rough prices have risen globally in the last six months by 5-10%.Diamond mining isn’t new to India and is said to have begun in the country in 4 AD along the Krishna river. Legend has it that the Kohinoor, once said to be the world’s biggest diamond, was mined near a rivulet in present-day Guntur district in Andhra Pradesh. Other famous diamonds such as the Great Moghul, the Regent and the Orloff have also been mined in India.Diamonds are an allotrope of carbon formed at high pressure and temperature. The layers of the earth where conditions are most favourable for their formation are referred to as ‘diamond stability fields’. These exist under the surface of the earth in the cratonic region at depths in excess of 150 km, Das Sharma told ET in an interview.As far as southeast India is concerned, there is a historical record of well-recognised kimberlite and lamproite emplacements in the eastern Dharwar (Karnataka) and Bastar ( Chhattisgarh ) cratons.“Our findings could lead to increased diamond mining in the country, but this will depend on the interests of mining companies. Diamond mining could become viable once an appropriate mining strategy is worked out,” Das Sharma told ET.