The experts have valued this gem recovered recently from the NMDC mine somewhere between Rs 2.5 and 5 crore.

"So far this 37.68 carat is the biggest ever diamond we have recovered from the Panna's Majjhgavan mines," National Mineral Development Corporation (NMDC) Assistant General Manager Rajeev Wadhwa told PTI here today. Panna mines is about 500 km from here.

NMDC officials said the white rough diamond of octahedron shape is of "good quality".

The mining major's Mumbai-based valuers will arrive in Panna sometime next month to assess the commercial value of the precious gem, Wadhwa said. The gem is expected to be auctioned later.

The previous big haul from Panna mines was in June 2010 when a 34.37 carat diamond was recovered.

Earlier, the mines had produced a 32 carat diamond in 2005 and a 30.30 carat diamond in 2003, which were sold for about Rs 1 crore each.

The Panna mines at Majjhgavan are Asia's biggest mechanised diamond mines and its diamonds are rated next only to those produced from South African mines.

NMDC, which is the only organised producer of diamond in the country, began its mining operations in Panna diamond mines in 1968 and since then it has unearthed a large number of diamonds from its pit.

The mining operations, which closed in Panna in 2005 for want of forest clearance and approvals from the adjoining Panna National Park, resumed in August 2009 after getting a conditional nod from the Supreme Court. Panna park is also a tiger habitat.

The Panna mines have an estimated reserves of 12 lakh carats of diamond.