Emerald together with aquamarine and beryl, belongs to the beryl group, being the most precious of the group. Its green is incomparable, and is therefore called “emerald green” (not only in mineralogy). The pigment is chrome, sometimes vanadium. The color is very stable against light and heat, and only alters at 700-800°C.
Only the finest qualities are transparent. Often the emerald is clouded by inclusions (liquid or gas bubbles,healing cracks and foreign crystals). 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” (gardens).
The most desired color is deep green which is the most valuable, even with inclusions, than a pale and clean quality. Distribution of color is often irregular, in spots or stripes. The luster is usually vitreous.
The physical properties of, especially the specific gravity and double refraction as well as pleochroism, vary according to source area. All emeralds are brittle and combined with internal stresses, sensitive to pressure; care must be taken in heating them. They are resistant to chemicals with the exception of fluoric acid.
The most important deposits are in Columbia first mined by the Incas.

*Info by Walter Schumann “Gemstones of the World”

*info by Walter Schumann ” Gemstones of the World”