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Emerald is a beryl, like aquamarine. One is green, the other blue, the difference between them being of a chemical nature. Emerald is a silicate of beryllium and aluminum occurring in nature as crystals of a hexagonal pyramidal shape. The dichroism of the stone is conspicuous, varying from pale green to grass green and dark green according to the chromium content. Hardness is 7.5 on the Mohs scale, and the substance is brittle; so great care is needed during cutting and setting and in preserving the stone.

Emerald was known in ancient times. It was initially mined in the Ural Mountains, Siberia and Egypt. Following Spanish colonization of South America, a number of old Inca mines were discovered, and these have since yielded some of the world's finest specimens. The Muzo, Cosquez, Chivor and Gachaia mines in Colombia are still worked today.

More recently, veins have been found in Brazil, South Africa, Zambia, Pakistan, Afghanistan and India, but none of these stones can equal the beauty of the Colombian specimens.

A flawless emerald is very rare. Indeed, identification of a stone is greatly facilitated by the presence of inclusions or even slight fractures. Most emeralds on the market today contain inclusions that diminish their transparency. Often the colour is irregular, the stone being darker on one side than on the other.

Emerald is without doubt the most imitated beryl. Synthetic stones are produced in Germany (Zerfass), United States (Chatham) and France (Gilson), and it would be extremely difficult for a layman to distinguish a natural from a synthetic emerald. Even expert jewelers can make mistakes, and the Chelsea colour filter which was originally designed to identify emeralds, has proved its limitations in certain dubious cases. In similar circumstances an entire series of scientific tests is called for. In simple terms, verification of an emerald could prove a very costly operation, so I strongly advise you to seek the assistance of a reliable jeweler with a reputation to defend.