Rare 10 Ct. Blue Diamond Fetches $21.5 Million at Sotheby’s

By Rob Bates | May 15, 2025

The Mediterranean Blue, an ultrarare 10.03 ct. fancy vivid blue diamond, fetched $21.5 million (17.9 million Swiss francs) in Sotheby’s High Jewelry auction in Geneva on May 13—making it “the most valuable diamond or jewel sold this year,” according to the auction house.

While the final price just topped the diamond’s presale estimate of $20 million, it showed there is still considerable interest in rare colored diamonds.

The stone’s price doubled from its opening bid of $10.7 million during a nearly three-minute bidding battle between two determined suitors. The winning bidder was described by Sotheby’s as “an American private collector keen to add the blue diamond to her collection.”

In a statement, Sotheby’s said that fewer than 0.1% of diamonds show any evidence of blue color, and an even smaller percentage are graded fancy vivid blue.

The 31.94 ct. rough diamond that yielded the Mediterranean Blue was found in 2023 at the Cullinan mine in South Africa. The cutter studied the rough for over a year.

Cullinan has been the source of the largest faceted colorless diamond in the world, the 530 ct. Great Star of Africa, as well as other notable fancy vivid blue diamonds, such as the 12.03 ct. Blue Moon of Josephine and the 15.1 ct. De Beers Blue.

(Photo courtesy of Sotheby’s)