Faith Nyasuguta
A rare blue diamond weighing nearly 42 carats has been unearthed at South Africa’s famed Cullinan Mine, reigniting global fascination with one of the world’s most storied diamond sources. Industry experts estimate the exceptional stone could fetch as much as $40 million when it eventually goes under the hammer, making it one of the most valuable diamond discoveries in recent years.
The gem, weighing 41.82 carats, was recovered by Petra Diamonds, which operates the Cullinan Mine located about 20 miles east of Pretoria. The company described the stone as a type IIb blue diamond of “seemingly exceptional quality,” praising both its vivid colour and high clarity. What has further captured attention is the diamond’s rough shape, which closely resembles the outline of the African continent, adding to its symbolic and collectible appeal.
Type IIb diamonds are among the rarest gems on Earth, accounting for less than 0.1 percent of all natural diamonds ever found. Their striking blue colour is caused by trace amounts of boron incorporated into the crystal structure deep within the Earth. These diamonds form under extreme pressure at great depths before volcanic activity pushes them closer to the surface, where they can eventually be mined.
Specialists are still studying the rough stone to determine the best cutting strategy. Petra Diamonds has said the goal will be to balance maximising the final polished size while preserving the diamond’s colour and clarity – an intricate process that can significantly influence its ultimate value. As with most rough diamonds, the finished gem is expected to be considerably smaller than its original weight.
Johannesburg-based diamond dealer Gregory Katz told media outlets that the stone could realistically command between $30 million and $40 million once cutting and polishing decisions are finalised. He described the discovery as “a significant find,” noting that high-quality blue diamonds of this size and classification rarely come to market.
The Cullinan Mine has a legendary reputation in the diamond world. It famously produced the Cullinan Diamond in 1905, the largest gem-quality rough diamond ever discovered. That historic stone was later cut into nine major diamonds, several of which now form part of the British Crown Jewels, cementing the mine’s place in gem history.
The discovery comes at a challenging time for the global diamond industry. Natural diamond prices have faced pressure in recent years due to weaker demand and the rapid rise of lab-grown alternatives, which offer consumers cheaper options. Against this backdrop, the Cullinan blue diamond is expected to attract strong interest from elite collectors and long-term investors seeking rare, natural stones.
Petra Diamonds has not yet announced when the diamond will be sold, but anticipation is already building. Once again, Cullinan has reminded the world why it remains one of the most extraordinary diamond mines on the planet.
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