Color : Emerald green, light green, yellow-green, dark green
Color of streak: White
Mohs’ hardness : 7.5-8
Specific gravity : 2.67-2.78
Cleavage : None 
Fracture: Small conchoidal, uneven, brittle 
Crystal system : Hexagonal
Chemical composition : Aluminium beryllium silicate
Refractive index : 1.576-1.582
Double refraction : 0.006
Flourescence : Usually none

The name emerald derives from the Greek Smaragdos, which in turn came perhaps from the Persian. It means “green stones.

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 vaanadium. The color is very stable against light and heat, and only alters at 1292-1472  F / 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 evidence as to the genuineness of the stone as compared with synthetic and other imitations. The expert refers to these inclusions as a “jardin” (garden).

The most desired color is a deep green which is more valuable, even with inclusions, than a pale and clean quality. Distribution of color is often irregular, in spots or stripes.