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 only alters at
1292-1472 degrees F (700-800 degrees C). The color distribution is often irregu-lar; a dark slightly bluish green is most desired.
Only the finest specimens are transparent. Often the emerald is clouded by inclusions (compare to page 58). These are not necessarily classified as faults, but are evidence as to the genuineness of the stone as compared with synthetic and other imitations. The expert refers to these inclusions as jardin (French-garden).
The physical properties, 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 them. 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. Deposits are found in biotite schists, clay shales, in lime-stones, with pigmatites. Mining is nearly exclusively from host rock, where the emerald has grown into small veins or on walls of cavities. Alluvial placers 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, especially the Muzo mine northwest of + mined by native tribes, the Muzo deposit was abandoned and redis-e 17th century. The mine yields fine-quality stones of a deep green , apart from shafts, is mainly by step-form