So last week we posted about the rare, flawless 7.59 blue diamond that is expected to sell for $19 million at Sotheby’s Hong Kong auction house. But now there’s a new rare fancy blue diamond on the market, that weighs 10.6 carats The radiant cut diamond has made headlines this week and is expected to fetch $9.8 million when it hits the auction house. The diamond has been named the M.S. Rau and is a stunning royal blue sky colour, with a VVS1 clarity grade, just one step down from being completely flawless. The diamond is set in a stunning platinum ring design with small round brilliant cut diamonds totalling 0.97 carats set on the shoulders and 96 vivid pink diamonds weighing 1.02 carats set around the radiant cut diamond in stunning rose gold. Blue diamonds are one of the rarest coloured stones that are extremely desirable in today’s diamond market. The blue colour occurs when a little bit of boron gets trapped in the carbon crystal of the stone.