TL;DR
The Mellon Blue, Bunny Mellon's 9.51-carat Fancy Vivid Blue diamond, sold for about $25.5 million at Christie's Geneva in November 2025 — roughly $7 million less than its 2014 record price. We tell the story of the storied stone, and what its softer result reveals about the market for great blue diamonds.
On the evening of November 11, 2025, a diamond the color of the deep sea crossed the block at the Four Seasons Hotel des Bergues in Geneva — and made headlines for something diamonds almost never do: losing money. The Mellon Blue, a 9.51-carat pear-shaped Fancy Vivid Blue diamond set in a platinum ring, sold for CHF 20,525,000, about US$25.6 million, at Christie's Magnificent Jewels sale, according to Christie's — the third-highest price ever paid for a vivid blue diamond at the house.
Here is the detail that turns a big number into a genuinely strange story: eleven years earlier, this exact stone had sold for $32.6 million. The Mellon Blue lost roughly $7 million between auctions — about 22% in nominal terms, nearly 60% after adjusting for inflation, Rapaport reported. Diamonds, the trade likes to say, are forever. Their prices, it turns out, are not.
Eleven years earlier: the night it set two world records
Rewind to November 20, 2014. Sotheby's was selling "Property from the Collection of Mrs. Paul Mellon: Jewels & Objects of Vertu" in New York — the estate jewelry of Rachel Lambert "Bunny" Mellon, who had died that March at 103. The star lot was her blue diamond pendant: 9.75 carats, graded Fancy Vivid Blue, estimated at $10–15 million.
Seven bidders opened; two private bidders dueled for about twenty minutes, and the hammer fell at $32,645,000 including buyer's premium — shattering two world records at once: the highest price ever paid for a blue diamond, and the highest price per carat for any diamond, at $3,348,205 per carat, as Rapaport reported at the time. The anonymous buyer was later revealed as Hong Kong billionaire Joseph Lau Luen-hung, who rechristened the stone the "Zoe Diamond" for his daughter, according to industry reporting. Between then and 2025, Lau had the stone recut to improve its clarity — 9.75 down to 9.51 carats, clarity up to VVS1 — Rapaport reported.
Why did the Mellon Blue lose money?
"The regression was shaped heavily by the broader market mood," Tobias Kormind, managing director of European online jeweller 77 Diamonds, told Rapaport: "Geopolitical tensions — from the war in Ukraine to [US President Donald] Trump's tariffs — and a weakened Chinese economy that kept many usual buyers away, left the room distinctly cautious." The irony: in 2014, the record was set by a Hong Kong buyer bidding aggressively from the phone. The stone didn't get less rare in eleven years — the world around it changed, and the auction record kept score.
The woman behind the name: who was Bunny Mellon?
Rachel Lambert "Bunny" Mellon (1910–2014) was an heiress, horticulturalist, philanthropist, and art collector. She was the daughter of Gillette company president Gerard Barnes Lambert and the granddaughter of Jordan Lambert, the inventor of Listerine; her second husband, Paul Mellon, was heir to the Mellon banking fortune.
Her quiet influence reached the center of American public life. In 1961, President John F. Kennedy personally asked her to redesign the White House Rose Garden — the design she produced with Perry Wheeler is essentially the garden the world knows today, as the garden's history records. She collected art on a museum scale — two Rothkos from her collection fetched $76 million at the same 2014 Sotheby's season that sold her diamond. She kept the blue diamond for decades as a pendant: a private pleasure, not a trophy.
What makes a diamond blue?
Natural blue diamonds get their color from trace boron in the crystal lattice — so scarce deep underground that blue diamonds make up less than 0.02% of all mined diamonds, according to Sotheby's, and roughly 0.1% fall in the Type IIb category, per the GIA.
The origin story reads like geology fiction. GIA researchers found that blue diamonds form more than 400 miles down in the Earth's lower mantle — about four times deeper than most diamonds — and that the boron that colors them likely arrived there from ancient seafloors, dragged deep into the mantle by subducting tectonic plates, as the study's reporting explains. The ocean may have written its signature into the Mellon Blue hundreds of millions of years before a cutter touched it.
One more party trick: most diamonds are electrical insulators, but Type IIb blue diamonds can conduct electricity.
That kind of rarity is why a blue stone in any jeweller's case deserves a second look. If this has you looking at colored gemstones in a new light, you can explore the gemstones at Lumière Gems — every stone's color is an accident of geology, and the blue ones are the rarest accidents of all.
Why are blue diamonds so expensive?
There is almost nothing else like them. Natural blue diamonds are less than one-tenth of one percent of all fancy colored diamonds, and Fancy Vivid — the Mellon Blue's grade — is the most saturated category the GIA awards. Going prices run roughly $30,000 per carat for faint blues to more than $1 million per carat for Fancy Vivid stones, per Sotheby's.
Provenance you can verify. The Mellon Blue carried a paper trail few stones can match: a celebrated owner, a world-record auction in 2014, a Christie's reappearance in 2025. Collectors pay for that story the way art collectors pay for exhibition history.
The room has to agree. A blue diamond's value is set in public, by bidders competing in real time. In 2014 the room agreed at $32.6 million; in 2025, a more cautious room agreed at $25.6 million.
Are all blue diamonds natural?
No — and the distinction matters. Blue diamonds can also be grown in laboratories by doping the crystal with boron during growth, producing the same optical color at 70–90% lower cost, according to trade guides. The Mellon Blue, for the record, is entirely natural — its boron arrived by plate tectonics, not by furnace. That is part of what the bidders in Geneva were paying for, even at a discount.
The stone is back in a private collection now, and if its history is any guide, it may be a decade before the public sees it again. It leaves behind an instructive record — a blue diamond that proved even the rarest things on Earth are worth exactly what the room is feeling on the night.