If the Wizard of Oz collects real emeralds, he’s doing pretty well for himself. Emeralds, the May birthstone, are a shiny shade of forest green, sometimes leaning more toward teal. They’re a variety of the mineral beryl, but only deeper shades are considered true emeralds.
Emeralds have a hardness of 7.5-8, making it one of the hardest gemstones just below rubies and sapphires. Like most gemstones, the darker the color, the more valuable the emerald. Because most emeralds have inclusions, or imperfections, a clear emerald is even more valuable.
Most premium emeralds come from Colombia, but they’ve been found in Russia and the U.S. as well. The Rockefeller emerald is the most expensive emerald sold to date, going for $5.5 million in 2017.