The Kazanjian Red Diamond, one of the most spectacular gemstones ever discovered, goes on display today at the American Museum of Natural History. Red is the rarest color in diamonds — less than 20 are known to exist in the world today. What’s more, the Kazanjian Red Diamond has an amazing back story. The gem was discovered in the 1920s in Litchenburg, South Africa. When found, it was a hefty 35 carats uncut. A diamond broker paid a modest eight pounds per carat for it. It was later sent to Amsterdam to be cut and polished by the Goudiv brothers....