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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 pegmatites. Gem-quality stones are found especially in the U.S., Brazil, Russia, and Madagascar.
This entry comes from Encyclopædia Britannica Concise. For the full entry on tourmaline, visit Britannica.com.