Emerald

The name emerald derives from Greek smaragdos. It means "green stone" and, in ancient times,  referred not only to emeralds but also probably to most green stones.

Emerald is the most precious stone in the beryl group. Its green is incomparable, and is therefore called "emerald green." The coloring agent for the "real emerald" is chrome. Beryls that are colored by vanadium ought to be called​​​​ "green beryl" and not emerald. The color is very stable against light and heat, and alters at 700-800 degree C. The color distribution is often irregular; a dark slightly bluish green is most desired.

Only the finest specimens are transparent. Often the emerald is clouded by inclusions. These are not necessarily classified as faults, but are evidence as to the genuineness  of the stone as compare with with synthetic and other imitations. The expert refers to these inclusion as jardin ( French -Garden ).
The physical property, especially the density, refractive index, and double refraction, as well as the pleochroism, vary according to source area. All emeralds are brittle and combined with internal stress, sensitive to pressure; care must be taken in heating the. They are resistant to all chemicals which are normally used in the household.

Deposits Emeralds are formed by hydrothermal processes associated with magma and also by metamorphism. Deposit are found in biotire schists, clayshales, in lime-stones, wtih pigmatites.

Mining is nearly exclusively from host rock, where the emerald has grown into small veins or on wall of cavities. Alluvial placer are very unlikely to come about as the density of emerald is near that of quartz. Therefore, rare secondary deposits are mostly formed by weathering.

Significant deposits are in Colombia, especial​​y the Muzo mine northwest of Bogota. First mined by native tribes, the Muzo deposit was abandoned and rediscovered in the 17th century. The mine yields fine quality stones of a deep green color. Mining apart from shafts , is mainly by step form terraces. The emerald bearing, soft broken rock is loosened with sticks, lately also through blasting or with bulldozers, and the emeralds picked out by hand. the host rock is a dark carbonaceous limestone. Accompanying minerals are albite, apartite, arangonite, barite, calcite, dolomite, fluorite, and pyrite.

Another important Colombian deposit, the Chivor Mine, is northeast of Bogota. It was also mined by Native Americans. The host rock is gray-black shale and gray limestone. It is mined in terrace, and also from shafts.

During recent decades further emerald deposits, which promise to be successful, have been found in Columbia. There is always a high demand for the rare, so called Trapiche emerald found exclusively in Colombia, a wheel like growth of several prismatic crystals. Only a third of the Colombian emeralds are worth cutting Stones larger than nut size are usually low quality or broken.

In Brazil there are various deposit in Bahia, Goias, and Minas Gerais. Stone are lighter than Colobian ones, mostly yellow green, but they are often free of inclusions. Through deposits newly discovered since the beginning of the 1980s, Brazil has become one of the most important suppliers of emeralds.

Since the second half of the 1950s, emerald deposits have been explored in Zimbabwe. Most important is the Sandawana mine in the south. Crystals are small, but of very good quality.

In the northern Transvaal (South Africa ), emeralds are mined by modern methods using machinery ( Cobra and Somerset Mines ). Only five percent of the production is of good quality. Most stone are light or turbid and only suitable for cabochons.

Emerald deposits were discovered in 1830 in Russia in the Urals north of Yeka