A rare blue diamond, passed between Europe's royal houses for more than 300 years, has been sold at auction for $6.7 million. Known as the Farnese Blue, the pear-shaped 6.16-carat jewel surpassed pre-auction estimates after going under the hammer for the first time at Sotheby's Geneva Tuesday evening. Originating from the Golconda mines in southern India, the fancy dark grey-blue diamond takes its name from the second wife of King Philip V of Spain, Elisabeth Farnese, who received it as a wedding gift in 1715. Over the next three centuries, the jewel was passed down to through generations of her descendants, which -- due to marriages between European houses -- saw it join the royal families of France, Italy and Austria. At one point in history, the Farnese Blue is thought to have appeared on a diamond tiara belonging to Marie Antoinette. The historic diamond was exhibited in London, New York, Singapore and Taipei, before arriving in Geneva ahead of yesterday eveni...