Emeralds as Gemstones
Emeralds are a very rare variety of a mineral called beryl. They are a deep green and rated as a gem. They are a chemical compound defined as Be3Al2(SiO3)6 and called beryllium aluminum silicate. Interestingly enough, emeralds must contain an impurity of chromium or vanadium (or a combination of the two). These impurities give emeralds their color.
As a crystal and a gemstone, emeralds are not as hard as diamonds. They register about 8 on the Mohs Scale. Emeralds frequently have inclusions and other deformities. These, in a limited amount, are thought to lend character to the stone, and to help differentiate natural stones from manufactured stones. A special cut was developed for the emerald because of the natural number of inclusions. The emerald cut is flat on its face and rectangular with facets around the edges.
Emeralds are valued based on properties of cut, color, clarity, and carat. The cut should be multifaceted and will most often leave the face as large and as smooth as possible. The darker the green, the better, and of course, the stone should be clear. Carat is the weight of the stone, which also determines size. Larger, more unusual natural stones will command a higher price. Many of the stones are oiled in order to obscure many of the inclusions. This practice is generally accepted in the gem trade, however, green tinted oils are frowned upon.
In recent years, it has become possible to manufacture Emeralds using hydrothermal synthesis. This requires very high temperatures (500-600°C) and very high pressures (700-1400 bars) as well as correct acidic and light conditions. There is usually a "seed" gem around which the crystalline structure of the Emerald grows. These synthetic emeralds are usually more perfect than emeralds found in nature, yet they are valued somewhat less.
Many countries do at least minimal mining for Emeralds, but the most prosperous mining centers are in Columbia where a certain "trapiche" emerald exhibits a star shaped pattern within its impurities. But emeralds are also mined in Zambia, Brazil, Zimbabwe, and other southern hemisphere locations. In the north, Russia and Canada also have emeralds.
The month of May boasts the Emerald as its birthstone. Human interaction with emeralds seems to have begun in ancient Egypt in mines south of present-day Cairo in about 2000 B.C. Egypt was the main supplier to Asia, Europe, and Africa until the middle ages, when mining ceased in Egypt. Once the New World was discovered Columbia became the source of the most spectacular emeralds. We find many references to Emeralds in literature, but the most famous is perhaps the Emerald City in Frank L. Baum's "Oz" books. The name is commonly used today to describe the lushly green city of Seattle, in the State of Washington. A reference to the "Emerald Isle" would trigger thoughts of Ireland in the minds of most people in the western world not because Ireland has more than its share of the gem, but because the climate has created a green landscape.
Ever since the first one was plucked from the ground and polished on the sleeve of some rough shepherd, emeralds have been much admired and have taken their place among the precious jewels of the world.