Top quality emeralds are a deep grass green with a slightly bluish cast. Lesser quality stones are lighter shades of green and can have a more yellowish tone. Fine, top quality emeralds are even more valuable than diamonds
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Emeralds are beryllium-aluminium-silicates with a good hardness of 7.5 to 8. They belong to the large gemstone family of the beryls, as does the light blue Aquamarine.
Pure beryl is colorless. The colors do not occur until traces of some other element are added. In the case of the emerald, it is mainly traces of chromium and vanadium which are responsible for the fascinating color.
Emeralds are found in many countries, but Columbia and Brazil are the major producers. Columbia is recognized as the source for the finest stones.
Emeralds usually contain many cracks, fissures, and inclusions. Because of this, the majority of these stones are "oiled". What this means is, they are immersed in oil which reduces the visibility of the inclusions. The oil also improves the clarity. It is important that the oil not be "washed" away by cleaning solutions.
Because emeralds are brittle stones, care should be taken when wearing or cleaning them. They should never be immersed in an ultrasonic or subjected to steam cleaning.