10 most expensive stones on Earth

The most expensive gemstones per carat aren't the biggest diamonds, they're the purest colors sold at auction. This countdown ranks ten record sales from a $115,000 alexandrite to the $57.7M Williamson Pink Star at $5.1M per carat, 191,000x gold. It traces the Regent Kashmir sapphire, Rockefeller emerald and Paraiba tourmaline, and explains why rarity doesn't equal price and why one ruby lost half its value in 8 years.