The ‘Ocean Dream’ has become the most expensive fancy vivid blue-green diamond ever sold at auction British international auction house Christie’s sold a rare blue-green diamond known as the ‘Ocean Dream’, which was found in Central Africa, for more than $17.3 million at its Magnificent Jewels sale in Geneva on Wednesday.  The auction house said the 5.5-carat diamond is the largest fancy vivid blue-green diamond ever certified by the Gemological Institute of America. It exceeded its presale estimate of $8-12 million. It was cut from an 11.70-carat rough stone found in the 1990s.  The gem was shaped into a triangular cut that preserved much of the original rough diamond.  Christie’s said the diamond attracted strong bidding before an unnamed private collector bought it. The bidding lasted around 20 minutes. The auction house said the final price set a new auction record for a diamond of its kind.…