
A remarkable 10-carat blue diamond, dubbed the “Mediterranean Blue Diamond,” is expected to achieve up to $20 million when it goes under the hammer at Sotheby’s in Geneva on 13 May. The diamond, which boasts the highly coveted “fancy vivid blue” colour grade, represents one of the most prized and rare categories in the world of coloured diamonds.
Discovered in 2023 at South Africa’s famed Cullinan mine, the Mediterranean Blue was originally a rough diamond weighing an impressive 31.94 carats. What followed was an extraordinary journey — a full year of study, including precise analysis to maximise both beauty and value, and six months of planning and expert cutting to reveal the gem in its final cushion-shaped form.
Sotheby’s, which is overseeing the auction, describes the diamond as a standout in its class. Jessica Wyndham, head of high jewellery at Sotheby’s Geneva, remarked, “The market for coloured diamonds continues to go from strength to strength.” Indeed, blue diamonds of this size and calibre are vanishingly rare, and collectors around the world are likely to compete fiercely for the chance to own such an exceptional gem.

Fancy vivid blue is the highest grading for coloured diamonds, denoting a saturation and purity of colour that few stones ever achieve. The Mediterranean Blue, with its intense oceanic hue and exceptional clarity, is a testament to nature’s rarity and human craftsmanship.
Over the years, similar diamonds have fetched extraordinary prices. In 2016, the “Oppenheimer Blue,” a 14.62-carat fancy vivid blue diamond, sold for a staggering $68.7 million at Christie’s in Geneva, setting a world record for any fancy vivid blue diamond sold at auction. That same year, another exceptional blue stone — a 24.18-carat intense blue diamond also mined from the Cullinan site — sold for $25 million, reinforcing the global appetite for ultra-rare coloured diamonds.
The Cullinan mine, known for producing some of the world’s most famous diamonds — including parts of the Cullinan I and II, which are part of the British Crown Jewels — has once again proven its status as a source of legendary stones.
With demand for coloured diamonds surging, particularly among high-net-worth collectors and investors seeking portable, tangible assets, the upcoming sale of the Mediterranean Blue Diamond is expected to draw worldwide attention.
Its appearance at auction not only marks a rare opportunity to acquire a gem of unmatched beauty and provenance, but also reflects the continuing strength and allure of the coloured diamond market — where rarity and story combine to create lasting value.