|Sotheby’s Hong Kong auctioned the largest and most valuable blue diamond ever - the 15.1 carat, internally flawless, fancy vivid step-cut De Beers Cullinan Blue. The 39.35 carat rough stone was discovered by Petra Diamonds in South Africa’s Cullinan mine in April 2021. The diamond has a value “in excess of $45 million.” There have been only five blue diamonds over 10 carats ever to appear at auction, and, until now, none of them has topped 15 carats.|
|Petra Diamonds (LON:PDL) 39.34 carat Type IIb gem recovered at its Cullinan mine in April
was sold to
De Beers and manufacturer Diacore
for $40.2 million.
Petra’s Blue Moon of Josephine diamond, cut from a 29.6-carat rough blue diamond, sold for $48.5 million in 2015.
The price of $4 million per carat remains the world record. The Blue Moon of Josephine lost about 59% of its mass during cutting. If the same holds for the 39.34-carat blue diamond, the result would be a 16-plus-carat gem. At $4m per carat, the polished stone would be worth $64m.|
Diamonds get their natural blue color from small amounts of boron trapped in the crystal carbon structure during its formation.