One of the most beautiful gemstones around, the emerald is the gemstone for May. This gorgeous green gemstone has been used by humans in jewellery for over 4000 years and remains in strong demand today. The emerald is the star of the beryl family of gemstones, overshadowing its more delicate coloured siblings, like the aquamarines, morganites and golden beryls. Emerald have a hardness in the range 7.5–8, and can be quite brittle.
We describe the colour of an emerald as being green but it is a colour that can vary between pure dark green to a bluish green to a softer forest green, with some yellow.
Historically, emeralds came mainly from mines in the Eastern Desert of Egypt, with some in Roman times from mines in Austria and a few from Afghanistan, until the discovery of the South American mines in the 16th century. These new mines produced larger stones with beautiful dark greenvcolours and with fewer inclusions. Columbian emeralds are still considered the finest stones. Emeralds are also mined now in Brazil, Zambia, and Zimbabwe, with many other smaller deposits found in other countries, including Australia.
Emeralds usually contain inclusions; in fact, the presence of these inclusions can be a good sign that the gemstone is natural and not synthetic. Because of these inclusions, most emeralds will have been treated in some way, but some treatments are more acceptable than others. Heating and oiling of emeralds using a colourless oil like cedarwood oil or Canadian balsam oil is an accepted treatment and has a long history in the industry. It is used to fill internal fissures inside emeralds which improves the colour. The treatment is a stable one but not permanent and should be disclosed, however, it is often considered to be industry practice and so well known that disclosure should not be necessary. Some emeralds are treated with coloured oils or resins such as opticon. The use of coloured oils must be disclosed to purchasers. There are other treatments but oiling and filling are the main ones used.