The Samarian Spinel
The gemstone on the left is the world's largest spinel. It is 5.5 cm (2.17 in.) wide and weighs 500 cts. The gemstone on the right weighs 270 carats and is the world's 4th larget spinel. The world's second largest spinel weighing 398.72 carats is set in the top of the Imperial Crown of Russia, and the world's third largest spinel. The Black Prince's Ruby, weighing 170 (140?) carats is part of the British Crown Jewels, set in the front of the Imperial State Crown, is also another large spinel.
The stone on the right in this photo, though smaller, has greater historical significance. It bears a 350-year-old inscription attributing it to Jehangir, the Mogul Emperor of India. According to legend, in response to criticism for having his name inscribed on the stone, Jehangir stated "This stone shall make my name more famous than the entire dynasty of Tamerlane." His prediction was at least partly correct, as Tamerlane's dynasty died out after 150 years, while Jehangir's name lives on inscribed on a number of gemstones in the Iranian treasury and foreign museums. This particular stone used on an armband for Nader Shah in 1739 AD.
The larger 500-carat stone has a hole in it. According to a diary entry of the court physician to Nasseridin Shah, the King told the physician that the stone once adorned the Golden Calf, and that a diamond later covered the hole. There is no way to confirm Nasseridin's Shah's fanciful description, and the diamond has since fallen off.