A ring is a round band, usually made of metal, worn as ornamental jewelry. The term ring by itself always denotes jewellery worn on the finger; when worn as an ornament elsewhere, the body part is specified within the term, e.g., earrings, neck rings, arm rings, and toe rings. Rings always fit snugly around or in the part of the body they ornament, so bands worn loosely, like a bracelet, are not rings. Rings may be made of almost any hard material: wood, bone, stone, metal, glass, gemstone or plastic. They may be set with gemstones (diamond, ruby, sapphire or emerald) or with other types of stone or glass.Emerald is a gemstone and a variety of the mineral beryl (Be3Al2(SiO3)6) colored green by trace amounts of chromium or sometimes vanadium.[2] Beryl has a hardness of 7.5–8 on the Mohs scale.[2] Most emeralds are highly included,[3] so their toughness (resistance to breakage) is classified as generally poor. Emerald is a cyclosilicate.