Emerald, the green kind of Beryl, is the most famous and helpful green gemstone. Its rich green colour, combined with durability and rarity, makes it one of the most valuable gemstones. Deep green is the most wanted colour in Emeralds. In general, the paler the colour of an Emerald, the lesser its value. Very pale-coloured stones are not called Emeralds but rather “Green Beryl”. They are sometimes heat-treated, which makes their colour turn blue and transform into Aquamarine.