Petra Diamonds found the second largest diamond in its history last week in the South African mine where the world’s biggest stone was found over a century ago.
The 425.1 carat diamond is a type II - the most collectable form which only makes up a fraction of global stocks. It is also completely colourless.
Analysts at the Royal Bank of Canada said the stone is likely to fetch between $25m and $35m ten years after Petra sold a similar 507 carat stone for a then-record $35m.
The miner also found a 101 carat diamond on 8 March this year.
“These stones reaffirm management’s message on: the prevalence of these higher value stone types at Cullinan; and that the mine’s plant is successfully recovering them,” said RBC analyst Tyler Broda.
“Any higher value stones will undoubtedly help to offset ongoing challenging price trends in lower value stones as was recently highlighted by a recent weak second sight from De Beers.”
The stone was found at the Cullinan mine, where explorers discovered the Cullinan diamond, a 3,106 carat beast in 1905. Two of the stones cut from the Cullinan were used to decorate the crown jewels.