emerald, the green variety of beryl, of which aquamarine is the blue variety. Chemically, it is a beryllium-aluminum silicate whose color is due to small quantities of chromium compounds. The emerald was highly esteemed in antiquity; the stones were used for ornaments in early Egypt where some of the first emeralds were mined. The finest emeralds are found in South America in Colombia, where they have been mined for over 400 years. The gem was a favorite in pre-Columbian Mexico and Peru, where it was cut in intricate designs. The treasure taken back to Spain by early explorers included emeralds. Good emeralds are the most highly valued of gem stones. India, Zimbabwe, and Australia are minor sources of the natural stones. Synthetic emeralds are also manufactured in Germany, France, and the United States. The Oriental emerald, a different gem, is the transparent green variety of corundum.