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 Emeralds, like all coloured gemstones, are graded using four basic parameters €the four Cs :- Colour, Cut, Clarity and Carat weight. Before the 20th century, jewellers used the term water, as in "a gem of the finest water, to express the combination of two qualities: colour and clarity. Normally, in the grading of coloured gemstones, colour is by far the most important criterion. However, in the grading of emeralds, crystal is considered a close second. Both are necessary conditions. A fine emerald must possess not only a pure verdant green hue but also a high degree of transparency to be considered a top gem. In the 1960s, the American jewellery industry changed the definition of "emerald" to include the green vanadium-bearing beryl as emerald. As a result, vanadium emeralds purchased as emeralds in the United States are not recognised as such in the UK and Europe. In America, the distinction between traditional emeralds and the new vanadium kind is often reflected in the use of terms such as "Colombian Emerald". The colour of an emerald is divided into three components, hue, saturation and tone. Emeralds in antiquity have been mined in Egypt since 1500 BC, and India, and Austria since at least the 14th century. Colombia is by far the world's largest producer of emeralds, constituting 50-95% of the world production, with the number depending on the year, source and grade. Zambia is the world's second biggest producer, with its Kafubu River area deposits (Kagem Mines) about 45 km Southwest of Kitwe responsible for 20% of the world's production of gem quality stones in 2004. In the first half of 2011 the Kagem mines produced 3.74 tons of emeralds. Emeralds are found all over the world.
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