what precious gems are the most expensive in the world
World's Most Expensive Gemstone Per Carat Sold at Auction. Identified as one of the unique gems in the world, a flawless blue diamond was honored in 2007 as the most expensive gemstone in the world. The 6.04-carat diamond was sold for $7.98 million at Sotheby's auction in Hong Kong. The flawless blue diamond fetched $1.32 million per carat.