6. Sapphire
Price per CD: $243,702
Sapphire, next on the list of most expensive gemstones in the world is a variety of corundum, which is aluminum-oxide. Sapphire comes in many colors (inclusions in corundum that can be iron, magnesium, copper or other elements), and the most famous are blue sapphires. The most famous variety is Kashmir sapphire, which comes from the Kashmir region of Pakistan and India.