The Ultra-Rare Mellon Blue Diamond is Coming to Christie’s Auction House this November
Christie’s Auction House announced today that one of the world’s most extraordinary diamonds is headed to the block: the Mellon Blue. This 9.51-carat Fancy Vivid Blue diamond, graded Internally Flawless, will be the crown jewel of the Magnificent Jewels auction on November 11 at the Four Seasons Hotel des Bergues in Geneva. With an estimate between $20 and $30 million, the Mellon Blue is far more than a dazzling stone—it carries a storied provenance, a touch of mystery, and the kind of rarity that has captivated collectors for generations.
Once worn by the legendary American philanthropist Bunny Mellon, the diamond has already made headlines as one of the highest-priced colored diamonds ever sold at auction. Now, more than a decade after its record-breaking appearance, it returns to the world stage, where its history, science, and glamour will once again be under the spotlight.
What is the Mellon Blue Diamond?
The Mellon Blue diamond is an exceptional Fancy Vivid Blue diamond weighing 9.51 carats, graded Internally Flawless, most recently set as a ring and estimated to sell between $20M and $30M.
The stone “is a rare expression of nature’s brilliance and remarkable for both its intense colour and its extraordinary purity,” says Christie’s in a press release. Indeed, blue diamonds are some of the rarest of colored diamonds, and the Mellon Blue’s flawless grade makes it even more exceptional. This is the second time in recent years that the diamond has been seen at auction—in 2014, the diamond was sold at Sotheby’s Auction House in New York for $32.6M, one of the highest prices paid for a colored diamond at the time.
Meet the Expert
- Rahul Kadakia has worked at Christie’s International Head of Jewellery since 1996 and was recently appointed as President in Asia Pacific and leader of the Global Luxury and Asian & World Art Groups
- He is one of the world’s most recognised auctioneers, overseeing Christie’s auctions in Geneva, Hong Kong, London, and New York, not only for Jewellery, Watches and Wine, but also Asian Art, Design, and Modern, Contemporary and Post-War Art.
The Mellon Blue and the Science of Blue Diamonds
Blue diamonds get their color from the presence of trace boron in their crystal lattice structure, which replaces some of the carbon atoms, allowing them to absorb red and yellow light, resulting in their stunning blue coloration. They typically form even deeper within the Earth’s crust than other diamonds, and while they may look similar to blue sapphires, the two stones couldn’t be more different: blue sapphires are made of corundum colored by titanium and iron, and are 10,000 times more abundant in nature.
The source of boron in the Earth’s mantle remains a geological mystery, though some scientists think it may have originated in ancient oceans where boron-rich materials were carried into the Earth’s interior through subduction zones—regions where oceanic plates are pushed deep beneath the planet’s surface. According to the Gemological Institute of America (GIA), their color can also be caused by radiation exposure or associated with hydrogen. Regardless of the exact process, the extreme combination of high pressure, heat, and boron impurities is so rare that these diamonds remain one of the scarcest fancy-colored diamonds.
The Mellon Blue and Bunny Mellon’s Legacy
The Blue Mellon diamond has a rich history and was most recently owned by Rachel Lambert Mellon, better known as Bunny Mellon, an American horticulturist, philanthropist, and art collector. “Bunny Mellon was a symbol of elegance and sophistication, and her refined taste extended to her jewellery, which she selected with the same care and sensitivity she brought to her interiors and gardens,” shares Christie’s in a press release. Bunny Mellon famously redesigned the White House Rose Garden with Jackie Kennedy in 1962 and designed the landscape for Hubert de Givenchy’s home. She also assisted with the restoration of the “Potager du Roi” at the Château de Versailles.
“Christie’s has sold nine of the top 10 jewels at auction in the first half of the year, driving year-on-year growth by 25%, with two various owner live auctions selling 100% in New York and in Geneva,” shared Rahul Kadakia, Christie’s International Head of Jewellery, in a press release. “We are now looking confidently to the second half of 2025 by announcing “THE MELLON BLUE”. This stunning Fancy Vivid Blue Diamond, once belonging to America’s Garden Queen, and is among the finest coloured diamonds to appear for sale at auction.”
