A model poses with an emerald and diamond tiara during a Sotheby's auction press preview on May 11, 2011 in Geneva. The tiara composed of 11 Colombian pear-shaped emeralds and weighing over 500 carats, was created for Princess Katharina Henckel von Donnersmarck and is alleged to be the most valuable tiara to have appeared at auction for over 30 years. It is expected to sell between US Dollars 5.1-10.2m, (Euros 3.5-7m) when it is auctioned at the Magnificent and Noble Jewels on May 17 in Geneva. AFP PHOTO / FABRICE COFFRINI