Emerald

Emerald is a gemstone and a variety of the
mineral beryl (Be3Al2(SiO3)6) colored green by
trace amounts of chromium and sometimes
vanadium. Beryl has a hardness of 7.5–8 on the
Mohs scale. Most emeralds are highly included, so
their toughness (resistance to breakage) is
classified as generally poor. Emerald is a
cyclosilicate. The word "emerald" is derived (via
Old French: esmeraude and Middle English:
emeraude), from Vulgar Latin: esmaralda/esmaraldus.