Emeralds have the richest green colour of gemstones. With a Moh’s hardness of 7.5 to 8, this gem is a precise combination of beryllium, silicon, aluminium and oxygen atoms.
Historians have estimated that the Egyptians mined emeralds as early as 3500 B.C. Indeed, Egypt was the major source of emeralds until the sixteenth century when the Spanish learned of the abundance of emeralds in the mines of Colombia. Today, this gem with the finest green among all coloured gemstones are mined in Colombia, Zambia, Brazil and Zimbabwe.
The most desirable colour of emeralds are bluish green to green, with strong to vivid saturation and medium to medium dark tone. Chromium, vanadium and iron are responsible for the colour of the emerald. The presence or absence of each of these minerals and their relative amounts determine the hue, tone and saturation of an emerald crystal.
Generally, the higher the chromium or vanadium content, the more intense the green colour. As the content of iron increases, so does the degree of blue in the emerald. Poor cutting would also greatly reduce the value of a finished piece of emerald.
Emeralds typically have inclusions that are visible to the unaided eye. The trade accepts the fact that most emeralds contain eye-visible inclusions. As such, eye clean emeralds are especially valuable as they are so rare.