Emerald, a Precious Gemstone

The name emerald derives from the Greek word "smaragdos" which means "green stones". Emerald is the most precious of the beryl group, which also includes morganite, yellow beryl and aquamarine, to name a few. Its green color is incomparable and therefore called "emerald green". The coloring agent for an emerald is chrome. An emerald's color is very stable against light and heat and only alters at 1292-1472 degrees Fahrenheit. The color distribution is often irregular, but a dark slightly bluish green is the most valuable.

Emeralds have a Mohn's hardness rating of 7.5 - 8, which makes them a great candidate for faceting and setting in jewelry. Their chemical composition is: Al₂ Be₃ Si₆ O₁₈ (aluminum beryllium silicate). They have a transparency of transparent to opaque and usually no florescence. Only the finest emeralds are transparent. The majority of emeralds are clouded by inclusions. These are not classified as faults, but are evidence that the emerald is genuine. An expert in gemology will refer to these inclusions as "jardin" a french word meaning garden. Emeralds are resistant to all chemicals used in the household but they are brittle and combined with internal stress are sensitive to pressure and heat.

Emeralds are formed in the ground by hydrothermal processes associated with magma and also by metamorphism. Deposits are found in clay shales, lime-stones, and in biotite schists. Mining is exclusively from a host rock where the emerald has grown into small veins or on walls of cavities.

Significant deposits are in Colombia, especially the Muzo mine northwest of Bogota. First mined by native tribes, the Muzo deposit was abandoned and rediscovered in the 17th century. This mine yields some of the finest quality stones with a deep green color. The emerald-bearing soft broken rock is loosened with sticks and then picked by hand. In recent years some of the larger deposits are mined by blasting or with bulldozers. The host rock at the Muzo mine is limestone and some of the other minerals found within that rock are: albite, apatite, aragonite, barite, calcite, dolomite, fluorite and pyrite. Colombian emeralds are the most valuable and sought after emeralds in the world and are usually marketed as such.

During recent decades further emerald deposits, which promise to be successful have been found in Colombia. In Brazil there are various deposits in Bahia, Groias and Minas Gerais. These stones are much lighter than Colombian emeralds and tend to be mostly a yellow-green, but are often free of inclusions. There are emerald mines in Zimbabwe and South Africa but only 5% of the production is of good quality. Most stones from this area are light or turbid and only suitable for cabochons. Further emerald deposits are in Russia, Afghanistan, Australia, India, Madagascar, Pakistan, Tanzania and the United States (North Carolina). The ancient emerald mines of Cleopatra (worked as early as 2000 B.C.) in upper Egypt are no longer worked and of historical interest only.

Due to very similar colors, emeralds can be confused with other green gemstones such as: demantoid, diopside, dioptase, fluorite, hiddenite and peridot. In order to hide very fine hairline fractures, emeralds are often dipped into special oils or prepared with artificial resin in a vacuum. This is usually done in the country of origin. In the United States, FTC guidelines require disclosure of any type of treatment to gemstones.

Emeralds are the birthstone of May and are said to heal headaches and sciatica.