The Mellon Blue Diamond | Exceptional Rarity

The Mellon Blue Diamond — a 9.51-carat Fancy Vivid Blue, Internally Flawless stone — will lead Christie’s Magnificent Jewels sale in Geneva on 11 November 2025, carrying an estimate of US$20–30 million.

Formerly part of the collection of Rachel “Bunny” Mellon, the diamond was last seen publicly in 2014 at Sotheby’s New York. Then weighing 9.75 carats and graded VVS2, it set a world auction record for a blue diamond at US$32.6 million. In the years since, the stone has been carefully re-cut to 9.51 carats, achieving the Internally Flawless clarity it now holds.

Blue diamonds of this caliber are among the rarest gems in existence. Their extraordinary color results from trace amounts of boron within the crystal structure, a natural phenomenon found in only a fraction of diamonds. To find one with such saturation, clarity, and size is a geological miracle — and to see it paired with flawless cutting is to witness the highest level of craftsmanship.

With its distinguished provenance, exceptional rarity, and remarkable refinement, the Mellon Blue stands as one of the most important diamonds ever to appear at auction.

Photography courtesy of Christie’s.
Gem Exploring Editorial.