(Beryl sample; image courtesy of Geology.com)
Beryl is the mineral family from which the emerald hails and is distinguished from other gems by its green colour. The emerald is considered one of the four cardinal gems. The green in this gemstone comes from trace amounts of chromium, vanadium and iron (to an extent) and the variations in the trace amounts of these elements that exist in the stone are what determine its (the emerald’s) worth and marketability. It is also this very same colour that holds the emerald as the standard for every green gemstone out there.
Since colour plays a major role in distinguishing one gem from the other (in most cases), we’ll begin with that. Emeralds range, in colour, from a yellowish green to a bluish green, the darker the tone of green in a stone, all the more obvious it is that the gem is an emerald. A light coloured stone (yellowish) suggests it may be a green beryl and not the cardinal gem.
(The Flagler Emerald From the Estate of Mary Lily Kenan Flagler; image courtesy of Sotheby’s.)
Emeralds are mostly cut in a cabochon (not faceted) and that can be owing to the disparity in hues and saturation occurring due to the fissures in the stone. Other than cabochon and an oval cut, emeralds have a certain cut that is rectangular in shape, faceted on the top.
Clarity, where the emerald is concerned, can practically be judged by the naked eye and this is because the fractures occur close to the surface; making the emerald susceptible to breakage. The stone has a hardness of 7.5 to 8 on the Mohs scale which should make it a hard stone but because of the surface breaking fractures and inclusions that occur in most emeralds, the stone isn’t considered durable but brittle.
(Emerald necklace by Cartier; image courtesy of Sotheby’s.)
In order to correct these sorts of impairments and to strengthen the gem while increasing the clarity, the emeralds are treated with oils that seep into the fractures and improve clarity of the stone significantly. Having said that, emeralds that have been treated with oils are worth less in most cases where the market for gemstones is concerned.
More about Emeralds in the next post.