introduce of tourmalin

Colors can vary from clear, to pink, rosy-red, yellow, honey, green, blue, violet, brown and black . Some crystals are pink at one end and green at the other. Concentric color zoning often occurs as well. The colored varieties, when transparent and flawless, are cut as gems.

Varieties of tourmaline, distinguished by their color due to the presence of certain minerals, have been given the following names:
Schorl (iron tourmaline) -- black 
Dravite (magnesium tourmaline) -- brown 
Rubellite (alkali tourmaline) -- pink 
Brazilian Emerald (alkali tourmaline) -- green
Achroite (alkali tourmaline) – colorless