A rare blue diamond weighing 41.82 carats has been recovered from the Cullinan mine in South Africa, with experts saying the stone could be worth more than $40 million. The company operating the mine described the diamond as being of exceptional color and clarity.
Grant Mobley, a gemologist and editor at Only Natural Diamonds Watch & Jewelry, said the stone ranks among the rarest finds on earth and could set a new record once cutting and grading determine its final worth.
The stone belongs to a classification called Type IIb, which accounts for roughly 0.1 percent of all natural diamonds, according to the Gemological Institute of America. Diamonds of this type form with boron present in their structure and almost no nitrogen. It is the boron that produces the blue color, as it filters out warmer wavelengths of light and allows cooler blue tones to dominate.
What makes extremely rare blue diamonds so scientifically unique
The company said this is the first significant blue stone pulled from Cullinan since a 39-carat rough blue diamond was found there in 2021 and eventually sold for more than $40 million. The mine has previously produced two other notable blue stones.
The De Beers Cullinan Blue, a 15.10-carat diamond, sold at auction in 2022 for $57.5 million, and the Blue Moon of Josephine, a 12.03-carat stone, sold in 2015 for $48.4 million.
Petra Diamonds has recovered a rare blue diamond from the Cullinan mine in South Africa. At 41.82 carats, the stone could break auction records once cut and graded. pic.twitter.com/o1NOyYLxKB
— Tom Marvolo Riddle (@tom_riddle2025) March 27, 2026
The newly found diamond is still being analyzed, and its final value will not be known until it is cut and graded. Before any cutting begins, specialists spend months studying the stone.
They need to understand how color sits within it and how the crystal is structured, so they can plan cuts that protect as much weight and color saturation as possible. A misjudged cut on a colored diamond of this quality can cost millions in lost value.
Cullinan’s record-breaking history and the road ahead
Cullinan has a well-established place in diamond history. The mine, which opened in 1902 and is expected to remain productive into the 2040s, produced the 3,106-carat Cullinan Diamond, the largest gem-quality stone on record, which was later cut into nine major gems now held in the British Crown Jewels. Petra reports annual production of between 1.4 million and 1.9 million carats over the past five years.
The find comes as the natural diamond market faces pressure from several directions. Prices for one-carat natural diamonds dropped as much as 26 percent between 2022 and 2025, according to Rapaport, driven by the growing popularity of lab-grown diamonds, reduced consumer spending, declining wedding rates, and trade pressures.
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