Gem Diamonds, the London-listed miner, yesterday unveiled a 196-carat diamond that was found last month at its mine in Lesotho.
The group said that the stone will attract a "substantial price" and that initial tests "indicate that it is expected to produce top colour and top clarity polished diamonds". The Government of Lesotho owns a 30 per cent stake in the mine.
Gem said that since buying the rights to the Letseng project four years ago, the mine has produced three of the world's top 20 biggest diamonds, including the 603-carat Letseng Promise, which was found in August 2006.
The find comes a year after fellow Southern Africa diamond miner Petra unearthed a 507-carat stone from its assets in near Johannesburg.
The Cullinan Heritage, the 19th largest diamond ever found, was sold to a Hong Kong jeweller in February for $35.3m.