A 10.02-carat Fancy Intense Blue diamond is expected to be among the top lots at Sotheby’s High Jewelry auction in New York this week, carrying a pre-sale estimate of more than $6 million.

The unmounted gemstone is a cut-cornered rectangular modified brilliant and has been positioned as the headline offering of the sale. According to Sotheby’s, the diamond is only the third Fancy Intense Blue stone weighing 10 carats or more to be offered at auction since 2008, highlighting the rarity of such material in the public market.

The auction house noted that the diamond’s colour saturation and size place it in a category seldom seen at international jewellery auctions. The stone is being offered loose, allowing the eventual buyer the flexibility to incorporate it into a bespoke jewellery design.

The High Jewelry sale also includes several other notable coloured diamonds, including a 6.76-carat Fancy Grayish Blue diamond and a 5.02-carat Fancy Intense Pink diamond, reflecting continued demand for rare fancy-colour stones among collectors and investors.

Blue diamonds remain among the rarest natural diamonds traded globally, with high-quality stones of significant size appearing infrequently at auction. Their scarcity and collector appeal have historically supported strong valuations in major sales.

The New York auction forms part of Sotheby’s annual High Jewelry calendar and features a mix of coloured diamonds, white diamonds and signed jewellery from leading maisons. Market observers will watch the outcome of the sale to gauge current appetite for exceptional natural coloured diamonds amid evolving luxury and investment trends.