Johannesburg - A 122.52 carat blue diamond has been discovered at Petra Diamonds' Cullinan mine, the company said on Friday.
“The rarity of a blue diamond of this magnitude sets it apart as a truly significant find,” Petra said in a statement.
Last year, Petra sold a 25.5 carat blue diamond for US16.9 million (around R181.9m at the present conversion rate).
In May, Christie's auction house sold a 13.22 carat pear-shaped diamond, the Winston Blue - the biggest flawless vivid blue diamond found - for US23.8 million (R256.5 million).
The Cullinan mine is the world's most important source of blue diamonds according to Petra. It bought the mine in 2008.
The mine is famous for the 3106.75 carat Cullinan diamond, found there in 1905. The two stones cut from it, the Great Star of Africa and the Second Star of Africa, are part of the Crown Jewels of the United Kingdom.
“The incredible rarity of blue diamonds, along with the rich history associated with many of the more important stones, has made them one of the world's most highly valuable and collectable items,” the company said.
The colour of blue diamonds is caused by small amounts of boron trapped in the crystal carbon structure when the diamond is formed.
The latest diamond would not be sold before the end of the month as it was being analysed to determine its value.