Petra’s 42-carat blue diamond sparks hope for natural gems

Africa-focused Petra Diamonds (LON: PDL) has unearthed an ultra-rare blue diamond weighing just under 42 carats at its Cullinan Mine in South Africa, a discovery that could sell for as much as $40 million and is already being described as one of the most significant diamonds recovered in modern times.

The rough stone, officially measured at 41.82 carats, belongs to the type IIb category, which accounts for less than 0.1% of all natural diamonds. Independent sector analyst Paul Zimnisky told MINING.COM the gem stands out even among elite finds.

“This stunning stone likely represents the largest high-quality fancy-blue diamond recovered in modern history and could easily be worth tens-of-millions of dollars, perhaps making it the most important diamond recovered this decade,” he said.

Petra said specialists are still analyzing the diamond to determine how it should be cut and when it may eventually come to market. Type IIb diamonds owe their prized blue colour to traces of boron, which absorb warmer tones, and stones of this size and quality are exceptionally rare.

Historic gems

Cullinan has a long track record of producing landmark stones. And fancy vivid blue diamonds larger than 10 carats have consistently commanded premium prices at auction.

The De Beers Cullinan Blue sold for $57.5 million in 2022, followed by the Mediterranean Blue, a 10-carat gem cut from a 31.94-carat rough discovered in 2023 and sold for $21.5 million at a Geneva auction in May 2025. 

In 2016, the 14.62-carat Oppenheimer Blue fetched 56.8 million Swiss francs ($71.3 million) at Christie’s in Geneva, setting a world record for a fancy vivid blue diamond sold at auction. That same year, a 24.18-carat intense blue diamond from Cullinan sold for $25 million, also in Geneva.

Zimnisky said the latest recovery reinforces Cullinan’s unique status in the global mining industry. “The Cullinan mine is certainly one of the most interesting and iconic mines in the world, across commodities,” he said.

“It has been in production since 1902 and has produced the largest gem-quality diamond in history, the 3,106-carat Cullinan Diamond, which was recovered in 1905 and currently resides in the British Crown Jewels. The mine has also produced most of the most valuable blue diamonds in the world, with the latest recovery added to the list.”

Located north-east of Pretoria, the Cullinan mine is expected to remain in production until the 2040s and continues to be a cornerstone asset for Petra.

Welcome boost

The discovery comes as the diamond industry faces weak demand, economic uncertainty and intensifying competition from lab-grown stones, pressures that have forced miners to cut costs, pause production and rethink their structure. Petra has struggled to generate sustained cash flow despite asset-streaming initiatives. 

Zimnisky said the high-profile find offers a rare boost for a battered sector. “This certainly represents some positive news for the diamond industry which has been hit from every angle the last few years,” he said. “The publicity around stones like this sell the ones bought by regular people.”

Petra confirmed Vivek Gadodia and Juan Kemp as joint CEOs in November after they had shared the interim role since February, with Gadodia leading corporate strategy and Kemp overseeing operations. Over the past year, the pair have focused on stabilizing the business while working through the company’s refinancing.

Looking ahead, Zimnisky said broader industry shifts could help lift sentiment. “2026 could be a pivotal year for the diamond industry with the potential for multiple meaningful catalysts including the sale of De Beers, a US trade resolution with India, and a new phase of natural diamond industry marketing via the Luanda Accord,” he said. “Sentiment has got so dire that we could very well be at a turning point just as few are expecting it.”