Cullinan Mine Unveils 42-Carat Type IIb Blue Diamond Valued at $40 Million
A rare blue diamond weighing 41.82 carats has been discovered at South Africa’s historic Cullinan Mine, reinforcing the site’s reputation for producing some of the world’s most exceptional coloured diamonds. Industry experts estimate the stone could fetch $30–$40 million at auction.
Petra Diamonds, which operates the mine approximately 20 miles east of Pretoria, described the find as a “type IIb blue diamond of seemingly exceptional quality in terms of both colour and clarity.” Specialists are still assessing the rough stone to determine the optimal cutting and sale strategy.
Type IIb diamonds are among the rarest in nature, accounting for less than 0.1% of all diamonds. Their distinctive blue hue comes from trace amounts of boron, forming at extreme depths before volcanic activity brings them closer to the surface.
The Cullinan Mine is legendary in the gem world as the site where the Cullinan Diamond—the largest gem-quality rough diamond ever found—was discovered in 1905. That historic stone was cut into nine major gems, several of which now feature in the British Crown Jewels.
Johannesburg diamond dealer Gregory Katz said the new find could command between $30 million and $40 million once cutting and polishing are complete.
He noted that while cutters aim to preserve size, the finished polished diamond will be smaller than the rough stone, highlighting the skill required to maximise its value.
The discovery comes amid challenging market conditions, with global diamond prices under pressure due to changing consumer spending and the rise of lab-grown diamonds, which offer a cheaper alternative to natural gems.
Despite this, the 42-carat blue diamond is expected to attract significant interest from collectors and investors, both in Africa and internationally. Petra Diamonds has not yet announced when the stone will go to market, but the mining and luxury sectors are watching closely.
