Composition : Complex silicate of aluminium and boron
Specific gravity : 3.02-3.26
Hardness : 7-7.5
Refractive index : 1.616-1.652
Birefringence : 0.014-0.021
Variety :
Pleochroïsm : distinct or strong according to the color
Cut :
Tourmalines are classified in several varieties according to their color:
Achroite : colorless and very rare
Rubellite : from pink to red according to its lithium content
Dravite : from yellow-brown to dark brown
Verdelite : all nuances of the green including green emerald
Indigolite or Indicolite : all nuances of blue
Siberite : from pink lilac to purplished blue
Schorl : black
Tourmalines of only one color are rather rare. A crystal can have ranges of the same color or several colors. The variety known as “Watermelon” is made of a red heart surrounded by a green cortex.
History :
Tourmaline takes from the Singhalese “turamali” whose exact meaning is not surely known (maybe "stone attracting ash")!
Tourmaline 
