An unknown Asian collector's flawless blue diamond was successfully bid by Moussaieff Jewellers in London for £4 million at a Sotheby's auction in Hong Kong, becoming the most expensive gemstone in the world. The 6.04 carat, internally flawless blue diamond fetched £650,000 per carat, having smashed a 20-year-old record held by the Hancock Red Diamond of Brazilian origin which fetched £450,000 per carat at the time.
Source: Dailymail