Since ancient times, the emerald has been synonymous with the colour green. Emerald belongs to the beryl family and is one of the 'Big Four' gems along with ruby, diamond and sapphire. The green colour in emerald is a result of tiny traces of chromium and vanadium. The stone can appear very deep, dark green to light green based on the amount of these elements. Of all the green colour gemstones, emeralds are the most beautiful and the most sought-after types. History records show that emeralds existed as early as 4000 BC. In several cultures, people worshipped emerald and considered it as the symbol of love and rebirth.
Colour of a gemstone is the distinctive feature that sets apart its beauty. It is also the crucial factor that determines the value of the stone. There are three components of colour that help in pricing an emerald: saturation, hue and tone. A bright and well-saturated stone is the most sought-after variety among emeralds.
Emeralds come in a range of blue-green to yellow-green, with green being the primary hue. The secondary colours are usually blue and yellow. However, with high levels of yellow or blue, the stone loses the 'emerald' status and becomes a different beryl type. The most popular emerald colours are green to bluish-green, with medium to medium-dark tone and vivid saturation. The stones with no visible colour zoning, even colour distribution and clear transparency are the most expensive emeralds.
At about seventy-five per cent tone, the colour green achieves its optimum saturation level, its gamut level. Grey is a natural mask or saturation modifier in emeralds and can reduce or dull the hue of the stone. For that reason, while purchasing, one should try to avoid gems with visible grey hues.
Beryl is a common mineral and is a part of many gemstones. For instance, yellow or orange Beryl is Heliodor and Morganite is Beryl in pink or salmon colours. The rarest type of Beryl is Bixbite which is a deep, intense red. Although emerald usually comes in intense, deep green, sometimes they are a light green colour or with a tinge of yellow.
The clarity of a diamond is graded by the loupe standard, i.e. 10x magnification. Emeralds, on the other hand, are graded by eye. That is because Emeralds have several surface-breaking fissures and inclusions. Therefore, an emerald becomes invaluable and flawless when it has no inclusions visible to the naked eye. Emeralds without such surface-breaking fissures are very rare. Most stones undergo "oiling" treatment to enhance the clarity of the gem. The rarest and most expensive emeralds are eye clean with an intense primary green colour. Such stones have no more than 15% of any secondary colour or a combination of a dark-medium tone.
The major sources of emeralds are Colombia, Brazil, Zambia, Afghanistan, Australia, Pakistan, Russia and the United States.