n.
Complex silicate mineral that is often used as a gemstone.
Three types of tourmaline, distinguished by the presence of certain elements, are usually recognized: iron tourmaline (schorl) is black, magnesium tourmaline (dravite) is brown, and alkali tourmalines may be pink, green, blue, or colourless. Tourmaline is most common in granite pegmatite s. Gem-quality stones are found especially in the U.S., Brazil, Russia, and Madagascar.