|Chemical composition||Be3Al2(SiO3)6 Beryllium aluminum silicate|
|Fracture||Conchoidal to uneven|
|Optic nature||Uniaxial -|
|Refractive index||1.566 - 1.600|
|Birefringence||0.004 - 0.010|
|Specific gravity||2.67 - 2.78|
|Pleochroism||Weak to distinct|
There are two schools of thought concerning whether green beryl colored by vanadium should be considered an emerald. The GIA considers it to be so, Gem-A does not. Up until about 40 years ago, no one considered vanadium beryl to be an emerald, despite known deposits such as those in Afghanistan and Pakistan. The Chelsea Colour Filter was developed specifically to separate emerald from vanadium beryl, as the chromium content in an emerald will make it appear red under the filter while the vanadium stones are inert.
In the early 1960's, large deposits of vanadium beryl were discovered in Brazil. Much to the frustration of the miners and dealers, the industry refused to consider this material as emerald due to it's lack of chromium content. In 1963, the GIA issued it's first lab report identifying vanadium colored green beryl as emerald. In their curriculum, they now teach that vanadium beryl is emerald.
However, this was not accepted by the entire industry. Whether they are or aren't still depends on to whom you are talking or on where you are doing your studies.
Vanadium emeralds tend to be less included than their chromium-colored brethren.