Petra’s 42-carat Blue Diamond Reignites Confidence in Natural Gems

The 41.82-carat blue diamond unearthed at the Cullinan mine in South Africa. (Image courtesy of Petra Diamonds.)

Africa-focused miner Petra Diamonds has uncovered an ultra-rare blue diamond weighing just under 42 carats at its Cullinan Mine in South Africa—an exceptional find that could fetch as much as $40 million and is already being hailed as one of the most important diamond recoveries of the modern era.

The rough stone, officially measured at 41.82 carats, falls into the Type IIb category, a class that represents less than 0.1% of all natural diamonds. These stones derive their coveted blue hue from trace amounts of boron, which absorb yellow tones during formation—making large, high-quality examples extraordinarily scarce.

Independent diamond industry analyst Paul Zimnisky described the discovery as a standout even among elite recoveries. He noted that the stone may be the largest high-quality fancy blue diamond found in modern history, with a value potentially reaching tens of millions of dollars and ranking it among the most significant diamond finds of the decade.

Still under evaluation

Petra Diamonds said specialist teams are continuing detailed analysis to determine the most suitable cutting strategy and the optimal timing for bringing the gem to market. Decisions around polishing and sale are critical, as the cut will ultimately define the stone’s final size, clarity and colour intensity—and therefore its value.

A mine with a storied legacy

Cullinan is no stranger to headline-making discoveries. Over more than a century of production, the mine has consistently delivered some of the world’s most iconic diamonds, particularly rare blue stones that command premium prices at auction.

In recent years, notable sales have reinforced this reputation. The De Beers Cullinan Blue sold for $57.5 million in 2022, while the “Mediterranean Blue”—a 10-carat stone cut from a larger rough recovered at Cullinan—achieved $21.5 million at a Geneva auction in May 2025. Earlier, in 2016, the 14.62-carat Oppenheimer Blue set a world record when it sold for 56.8 million Swiss francs ($71.3 million) at Christie’s in Geneva. That same year, a 24.18-carat intense blue diamond from Cullinan fetched $25 million.

Zimnisky said the latest discovery further cements Cullinan’s unique standing in global mining. In addition to producing the famed 3,106-carat Cullinan Diamond in 1905—now part of the British Crown Jewels—the mine has yielded many of the most valuable blue diamonds ever sold.

Located northeast of Pretoria, Cullinan is expected to remain in operation until at least the 2040s, continuing its role as a cornerstone asset in Petra’s portfolio.

A timely boost for the industry

The discovery comes at a challenging time for the global diamond sector. Weak consumer demand, economic uncertainty and rising competition from lab-grown diamonds have forced many producers to cut costs, suspend output and restructure operations. Petra itself has faced pressure to improve cash flow despite various asset-streaming initiatives.

Against this backdrop, Zimnisky believes the high-profile recovery offers a welcome lift for sentiment. He noted that headline stones like this help reinforce the allure of natural diamonds, supporting demand across the broader market.

Petra recently confirmed Vivek Gadodia and Juan Kemp as joint chief executives after serving in interim roles, with a renewed focus on stabilising the business and advancing refinancing efforts.

Looking ahead, Zimnisky said 2026 could mark a turning point for the diamond industry, citing potential catalysts such as the sale of De Beers, improved US-India trade relations, and renewed global marketing initiatives for natural diamonds under the Luanda Accord.

With sentiment at historic lows, he suggested the Cullinan blue diamond may arrive just as the industry begins to rediscover its sparkle.