Rare 5.50-Carat Blue-Green Diamond 'Ocean Dream' Sells for $17.3 Million at Christie's Geneva

The 5.50-carat natural blue-green diamond known as the Ocean Dream sold for $17.3 million at a Christie's auction in Geneva in May 2026, roughly doubling its previous auction price from 2014.

According to international auction house Christie's, the Ocean Dream is classified as a Fancy Vivid Blue-Green diamond and is considered the largest known diamond in its specific colour category. The triangular-cut gemstone has an SI1 clarity grade and weighs 5.50 carats. Its original rough stone weighed 11.70 carats and was discovered in Central Africa during the 1990s before being cut and polished.

History and Exhibition

• Smithsonian Display: In 2003, the diamond was featured in "The Splendour of Diamonds" exhibition at the Smithsonian National Museum of Natural History in Washington, DC, alongside other notable gemstones such as the De Beers Millennium Star and the Steinmetz Pink.
• Auction Record: The diamond previously sold at Christie's Geneva in May 2014 for approximately $8.5 million (CHF 7.7 million).
• May 2026 Sale: The stone returned to Christie's Geneva, fetching CHF 13.56 million (approximately $17.3 million), exceeding its presale estimate of CHF 7 million to CHF 10 million.

Formation and Rarity

Natural coloured diamonds develop their hues due to structural differences and impurities. In the case of green diamonds, natural radiation over geological periods interacts with the crystal structure, displacing carbon atoms to create colour centres that alter light absorption. While radiation often affects only the outer layers, the Ocean Dream's vivid appearance throughout makes it exceptionally rare.