Emerald – May Birthstone
Emeralds are a form of beryl, like aquamarines, and have been mined and used in jewellery for thousands of years. Somewhat· confusingly, the word “emerald” was used until the late 19thC to refer to all green stones. The geographical origin of a stone is vitally important to its value. Most emeralds come from Colombia, the most sought-after from the Muzo and Chivor mines. Emeralds are also found in the Urals, Siberia, East Africa, India and Pakistan. There is also an important deposit at the Sandawana mine in Zimbabwe. Some of the most important surviving emerald Jewellery was made in 16thC India, and it was originally thought that the stones were Indian; it is now known that the emeralds were brought to India from Colombia by the Spanish. These older Colombian stones are of better quality than those mined today, the best deposits having been exhausted.
Some of the good-quality old stones have been recut, so that it is possible for a modern-looking gemstone really to be old material reused.
Unlike diamonds and sapphires which vary in colour, emeralds are only ever green. Their colour results from the presence of chromium, though there may also be traces of vanadium, the pigment found in violet sapphires. The best stones from the Muzo mine in Colombia are a rich, deep grass green with a slight yellow tinge and at the same time a flash of blue. The lesser-quality stone show lack of depth or brilliance. Although emeralds, when viewed separately, may seem to be uniform in colour, when they are compared with each other, the differences in hue are obvious. Stones from the Sandawana deposit in Zimbabwe are sometimes almost flawless, and are a deep green, darker than Colombian stones, with a blackish tinge and no hint of yellow. Siberian or Ural emeralds tend to be a paler mid-green and are of lower value. Almost colourless emeralds are sometimes found, and in past centuries these were set with green foil backs to intensify their colour. In its natural state, the emerald is formed in a long hexagonal system, rather like a stick of candy, which runs through its host rock.
It is extremely rare to find a finely coloured emerald without inclusions; even in the good-quality stone these are visible. An emerald with few or no inclusions may well be cause for suspicion. Most emeralds seen on the market today are heavily flawed, sometimes extremely so. Siberian and Ural stones tend to be the most included, which lends the stones a milky, rather dull appearance.
Many modern emeralds have been “oiled” – the inclusions are filled with natural petroleum oil – and this treatment is termed “enhancement”. It is not so acceptable in the gemmological field for inclusions to be filled with coloured resin or synthetic oils.
Emeralds are soft and very brittle compared to other gemstones, and are therefore easily damaged. Check stones carefully for chips or abrasions due to wear. Because of their delicacy, great care should be taken in setting and unsetting emeralds. Emeralds should be set with gold rather than platinum claws because the latter metal can scratch the stone’s surface.
In 17thC Mughal India emeralds were often cut as hexagons, richly engraved with scrolling flora and foliage, and occasionally birds. Many were extremely large, over 100ct, and were worn unmounted as pendants. Many of these stones were later exported and mounted as brooches by Western jewellers. Partly to make them less susceptible to being knocked and partly to enhance the colour, a version of the rectangular step-cut with cut corners was developed in the mid-19thC. (This has become known as the “emerald cut” because it is so often used for this stone. Superior-quality emeralds are also multi-faceted, as in cushion cut and mixed-cut rings. More flawed stones are usually cut as cabochons or as beads for necklaces. Occasionally, they are also cut as cameos or intaglios but, due to the risk of splitting, this is a difficult technique.
To own Emerald is to own a piece of history, a piece of nature and work of art. Each one is truly individual. With its array of inclusions and clouds, the gem is not fame for its crystal clarity, but is steeped in so much history that we automatically ignore the gem’s imperfections when we study a piece and accept that these impurities are simply “ the fingerprints of Mother Nature”.