Cullinan Mine Delivers Again: Petra Unearths Rare 41.82-Carat Blue Diamond

Petra Diamonds has once again reminded the jewelry world why South Africa’s Cullinan Mine holds near-mythic status. On Tuesday, the miner announced the recovery of an extraordinary 41.82-carat blue diamond — a rare Type IIb stone noted for its striking color and clarity.

Even in rough form, the gem is arresting. Its deep, saturated blue hue and apparent transparency place it among the most important blue diamond discoveries of recent years. Petra described the stone as being of “seemingly exceptional quality.”

Blue diamonds are among the rarest of all natural diamonds, with their color caused by trace amounts of boron absorbed deep within the Earth. Type IIb diamonds account for less than half of 1% of all diamonds ever discovered. Many form 300 miles or more below the Earth’s surface, far deeper than most other diamonds, which only adds to their mystique.

What excites collectors and connoisseurs alike is the stone’s potential future. Based on historical recovery rates of around 30 to 40 percent, expert cutters could fashion a polished “hero” diamond weighing approximately 14 to 18 carats. That range is particularly compelling because it aligns closely with the most famous and valuable blue diamonds ever sold at auction.

Among them are the following: the 14.62-carat Oppenheimer Blue, which fetched $57.5 million at Christie’s Geneva in 2016; the 15.10-carat De Beers Blue, sold by Sotheby’s in 2022 for $57.47 million; and the 12.03-carat Blue Moon of Josephine, which achieved $48.5 million in 2015. More recently, the 17.6-carat Bleu Royal brought $43.8 million at Christie’s in 2023. Should Petra’s new discovery yield a polished diamond of comparable size and quality, it could one day join this elite group.

The Cullinan Mine’s legacy only deepens that possibility. The historic deposit (renamed from the Premier Mine in 2003) famously produced the 3,106-carat Cullinan Diamond in 1905 — the largest gem-quality diamond ever discovered — as well as a remarkable lineage of celebrated blue diamonds over the past century. In recent years alone, the mine has yielded multiple high-value blue stones that have gone on to set price-per-carat benchmarks.

Petra Diamonds is currently analyzing the rough stone to determine the optimal cutting strategy and eventual method of sale.

Credits: Images courtesy of Petra Diamonds.