Emeralds are a variety of the mineral beryl (Be3Al2(SiO3)6,) colored green by trace amounts of chromium and sometimes vanadium. Hurlbut, Cornelius S. Jr, & Kammerling, Robert C., 1991, Gemology, p. 203, John Wiley & Sons, New York Beryl has a hardness of 7.5 - 8 on the 10 point Mohs scale of mineral hardness. Most emeralds are highly included, so their toughness (resistance to breakage) is classified as generally poor. The word "emerald" comes from Latin smaragdus, via Greek smaragdos, its orig… (More on Emerald)