Mohs scale of mineral hardness
Emerald (Tamil: மரகதம்)is a variety of the mineral beryl (Be3Al2(SiO3)6) colored green by trace amounts of chromium and sometimes vanadium. The hardness of Beryl is 7.5–8 on the 10 point Mohs scale of mineral hardness. The toughness (resistance to breakage) of Emerald is classified as generally poor, hence most emeralds are highly included.