The emerald is another variety highly prized in jewelry, and distinguished by its deep color, which is probably due to the presence of a little oxide of chromium
a valuable stone that is usually green or yellow (beril, from beryllus, from beryllos). Mineral composed of beryllium aluminum silicate, Be3Al2(SiO3)6, a commercial source of beryllium. Several varieties are valued as gemstones: aquamarine (pale blue-green); emerald (deep green); heliodor (golden yellow); and morganite (pink). Before 1925 beryl was used only as a gemstone, but since then many important uses have been found for beryllium (e.g., in nuclear reactors, space vehicles, and X-ray tubes). No large deposits have been found, and most production is a by-product of the mining of feldspar and mica. Brazil is a major producer; others include Zimbabwe, South Africa, Namibia, and the U.S