In an indication of growing fondness and market for coloured stones ahead of this holiday season, a large blue diamond, one of the world's rarest, could fetch $35 to $55 million at Sotheby's auction next week. The stone was discovered in South Africa's famed Cullinan mine in January 2014 and cut into a cushion shape from a 29.62 carat rough crystal. Its current owner, New York-based jeweler Cora International, bought it from Petra Diamonds, the mine's owner, according to Sotheby's.The rare stone was discovered in South Africa's famed Cullinan mine in January 2014 and cut into a cushion shape from a 29.62 carat rough crystal. Its current owner, New York-based jeweler Cora International, bought it from Petra Diamonds, the mine's owner, according to Sotheby's.

As David Bennett, worldwide chairman of Sotheby's international jewelry division, says about the  blue diamond, "The market for vivid blue diamonds of this level, it's so rare. Each stone is individual, in a sense. The GIA (Gemological Institute of America) graded 400 blue diamonds and only four of the 400 were graded (fancy) vivid blue. So even amongst this extremely rare class of blue diamonds, to get one vivid blue, 12 carats, internally flawless, is once in a blue moon.