The stone would dwarf the Koh-i-Noor diamond in the British Crown Jewels
Miners in Lesotho have discovered a huge gem stone which may become the largest ever polished round diamond.
The stone weighs 478 carats and is the 20th largest rough diamond ever found, said Gem Diamonds.
The company said the uncut rock was recovered recently from the Letseng mine, owned by the company in Lesotho.
The diamond, which is as yet unnamed, has the potential to yield a 150 carat cut stone, and could sell for tens of millions of dollars, the company said.
"Preliminary examination of this remarkable diamond indicates it will yield a record-breaking polished stone of the very best colour and clarity," said the company's chief executive Clifford Elphick.
It would be bigger than the 105 carat round-cut Koh-i-Noor diamond, which is part of the British Crown Jewels.
It would still be dwarfed by the Cullinan diamond discovered in 1905, which was 3,106 carats uncut and yielded a teardrop shaped diamond of 530 carats called the Great Star of Africa.
The Letseng mine is owned by a mining company of which Gem Diamonds controls 70% and the Lesotho government 30%.