Emerald is the green to bluish green variety of beryl, a mineral species that also includes aquamarine as well as beryls in other colors.
Emeralds
Emerald is a gemstone and a variety of the mineral beryl colored green by trace amounts of chromium and/or sometimes vanadium. Most emeralds are highly included, so their toughness is classified as generally poor. Emerald is a cyclosilicate.