Beryl is the name given to a family of six chemically related stones, including aquamarine, bixbite, emerald, goshenite, heliodor, and morganite. All beryls are considered precious stone and are composed of Be3Al2(Si6O18). They form according to a hexagonal crystal structure, and have a hardness of 7.5-8 on the Mohs scale. *Please see Emerald and Aquamarine in their own listing.