Petra Diamonds has sold a 20.08 carat blue diamond found at South Africa’s famous Cullinan mine for $14.9m (£11.49m).
The company said that this was equivalent to roughly $741,000 per carat.
It added that the buyer was a leading diamond company that wished to remain anonymous.
Richard Duffy, Petra’s chief executive, said: “We are very pleased with this result which is in line with our expectations and confirms the resilience in the value of very high quality blue diamonds, undoubtedly one of nature’s rarest treasures.
“We look forward to following this exceptional stone’s journey to its polished form.”
The sale is especially good news for Petra as in September the independent diamond company announced a double-digit fall in annual profits as a result of weak prices.
London’s largest diamond mining group reported adjusted core profit of $153m in the 12 months to 30 June, plunging 22 per cent from the previous year.
This year has proved challenging for diamond sales so far, with a combination of oversupply, ongoing trade tensions and increased sales of lab-grown diamonds all responsible for a decline in sales.
The Cullinan mine is renowned as a source of the extremely rare blue diamond, as well as the site of the discovery of the largest rough gem in history, the eponymous Cullinan diamond.
Clocking in at 3,106 carats, this stone was cut in half, with the resulting pieces forming part of the UK’s crown jewels.
In recent years, the Blue Moon of Josephine, a 12 carat gem from the mine, sold for $48.5m, or $4m per carat.
Main image credit: Petra Diamonds