Emerald, the birthstone for May, is the gemstone variety of the mineral beryl, and is the most popular green gemstone in the world.
The history and mythology associated with emerald is vibrant and complex, but it is generally seen to symbolize growth, peace, healing and fertility. It's also the official anniversary gemstone for commemorating the 20th and 35th years of marriage.
Emerald is well-known for its green color, but is found in various shades of green ranging from a blueish to slightly yellowish. The stone is, by definition, rich in color – stones with light tones are normally called “green beryl” instead of emerald, but this isn't a rule in all countries.
As with diamond, the way an emerald shines is affected by inclusions and surface-reaching fractures. It's rare to find an emerald that does not have inclusions which are visible with the unaided eye, and under low magnification most emeralds are actually shown to have a great number of them.
Emerald measures between 7.5 and 8 on the Mohs scale. However, inclusions and fractures can make the stone weaker than its place on the scale would suggest, and this is why emerald jewelry is better saved for special occasions than worn daily. It's also better suited for earrings and pendants, which are usually less exposed to impacts than rings and bracelets.
Emerald is rare because there are only small amounts of beryllium in the Earth's crust, and the optimum conditions for the element are different to other necessary elements that give the stone its color – chromium and vanadium. Colombia is by far the world's largest source of emerald, and emeralds sold in North America are normally Colombian.
The word emerald has been derived from similar Latin and Greek words meaning “green gem”.
According to the world's oldest book, the Papyrus Prisse, "good words are more difficult to find than the emerald, for it is by slaves that it is discovered among the rocks." It probably refers to gemstone mines thought to have been used by Egyptian pharaohs between 3000 and 1500 B.C.
Emeralds have been a popular choice with rulers throughout history, from Cleopatra, to Alexander the Great, to Queen Elizabeth II. The Incas and Aztecs of South America, where the best emeralds are still found today, considered emerald a holy gemstone, and in the 16th century Spanish conquistadors looted thousands of the stones from South American mines. Since then, royalty in many different countries have looked to South America for supplies of emeralds for rings, necklaces, bracelets and crowns.
Today, emeralds are commonly worn by celebrities, popularized in part by actress Elizabeth Taylor.
As with diamond, emerald is graded using the basic four parameters of color, cut, clarity and carat, each of which can affect its value.
The most important attribute is color, closely followed by clarity – a fine emerald must have not only a vivid green hue, but also a high level of transparency to be considered a top gem. However, while diamonds have their clarity graded at 10x magnification, emeralds are graded by eye. This means an emerald with no inclusions visible by the unaided eye is considered flawless.
The most valuable color is a slightly bluish green in a medium dark tone, with strong to vivid saturation. Emeralds of the highest quality can be more expensive than diamonds.
Most emeralds are oiled in order to fill in surface-reaching cracks, which improves their clarity and stability. While this is accepted practice, oil-treated emeralds are worth much less than untreated emeralds of similar quality. Other treatments, such as the use of green-tinted oil, are not acceptable in the trade.
Emerald treatment is graded on a four-step scale, from none, to minor, to moderate, to highly enhanced.
Emerald's vibrant green color and mysterious rarity has made it a popular choice for jewelry for thousands of years.
It is one of the 'big four' gemstones, along with diamond, sapphire and ruby, for the way it has been consistently prized over the centuries. However, despite its beautiful hue it is the least durable of the four. With that in mind, people need to take extra care of their emerald jewelry.