Green Emerald Gemstone Emerald is perhaps the most famous of green gemstones. It is also certainly one of rarest and most valuable. Green emerald is the most precious member of the beryl group, and it is even classified as one of the 'precious four' gemstones - which also includes ruby, sapphire and diamond. In the world of colored stones, the green color of emerald is unparalleled. Its color is owed to traces of chromium and in some cases, vanadium. Like all beryl, emerald has excellent hardness and durability, although some heavily included emerald stones may be more fragile than others. The finest emerald is thought to come from Colombia, followed by Brazilian and African emerald. Nearly all emerald is color and clarity enhanced through a routing oiling process, usually done right at the mining source.