The Mellon Blue Diamond
This exceptional 9.51-carat, Fancy Vivid Blue, Internally Flawless, pear-shaped diamond has been confirmed as the headline lot of Christie’s Magnificent Jewels auction in Geneva on 11 November 2025, carrying an estimate of US$20–30 million.
Significance
Peak color and clarity. “Fancy Vivid Blue” is the highest saturation grade in the GIA color scale. At more than nine carats, with Internally Flawless clarity, the Mellon Blue Diamond belongs to the most exclusive category of natural colored diamonds.
Illustrious provenance. The gem was owned for decades by Rachel Lambert “Bunny” Mellon, the distinguished American horticulturist, philanthropist, and tastemaker whose impeccable eye and refined style remain legendary.
Auction spotlight. The Mellon Blue Diamond will be previewed in Hong Kong and Geneva before taking center stage in Geneva this November.
Journey through history
The Mellon Blue Diamond has already made auction history. In 2014, a 9.75-carat, pear-shaped Fancy Vivid Blue diamond from Bunny Mellon’s collection was sold in New York for US$32.6 million, at the time setting a world auction record for a blue diamond. That stone carried a GIA report describing it as VVS2 clarity with a “working diagram” noting its potential to be polished to Internally Flawless.
Today, the Mellon Blue is described as 9.51 carats, Internally Flawless, Fancy Vivid Blue and mounted as a ring. The slight difference in weight and the elevation in clarity are consistent with a careful repolishing since 2014, though Christie’s has not released technical details. For gemologists, this is an instructive reminder of how a diamond’s life continues long after its first cutting.
For the Curious
Color origin. Natural blue diamonds typically owe their hue to trace boron atoms within the crystal lattice, and are most often classified as Type IIb. While Christie’s has not released the type classification for this diamond, Fancy Vivid blues in this size are extraordinarily rare.
Significance of Vivid. In GIA grading, “Fancy Vivid” represents the strongest possible color saturation. At near-ten carats, the Mellon Blue Diamond sits in a category with only a handful of known comparables.
Due diligence. The new GIA grading report will be available in the auction catalogue, providing full verification of weight, clarity, and color origin.
Symbol of rarity
Blue diamonds represent less than 0.02% of natural diamonds, and very few combine vivid saturation, flawless clarity, and exceptional size. The Mellon Blue Diamond, with its elegant pear cut and remarkable provenance, embodies the pinnacle of rarity and refinement.
When it comes under the hammer in Geneva this November, it will not only be a test of the market for colored diamonds—it will reaffirm the enduring fascination of gems that carry both natural beauty and cultural legacy.
Photography courtesy of Christie’s.
— Gem Exploring Editorial.
