The emerald stone has captivated nations and civilizations for almost 4,000 years. Emeralds are named after the mineral cryolite, which is an ore of mercury. The word "emerald" is derived from the Greek emerenthon, meaning "quicksilver." Although mercury is a toxic substance, the ancient Greeks used it in medicine because of its holiness. It was only banned by an EU law in 2004. Before that, people had no idea how dangerous it was. Even though we now know better, some people still believe that emeralds can cure diseases and offer protection against evil eyes. In mythology, the goddess Athena was often represented as wearing an emerald helmet. This shows that the ancient Greeks too knew about the lucky properties of emeralds. They also used them in jewelry to represent wisdom. Today, they are mostly used in gemstones because of their beautiful color. The best emeralds come from India, although there are also good ones found in America and Africa. In fact, all green gems are called emeralds. But not all emeralds are equal. There are two main types: flawless and flawed. Flawless emeralds are very rare (about 1% of the world's supply).