Tourmaline has a variety of colors. Usually, iron-rich tourmalines are black to bluish-black to deep brown, while magnesium-rich varieties are brown to yellow, and lithium-rich tourmalines are almost any color: blue, green, red, yellow, pink, etc. Rarely, it is colorless. Bi-colored and multicolored crystals are common, reflecting variations of fluid chemistry during crystallization. Crystals may be green at one end and pink at the other, or green on the outside and pink inside; this type is called watermelon tourmaline. Some forms of tourmaline are dichroic, in that they change color when viewed from different directions.
Some tourmaline gems, especially pink to red colored stones, are altered by heat treatment to improve their color. Overly dark red stones can be lightened by careful heat treatment. The pink color in manganese-containing near-colorless to pale pink stones can be significantly increased by irradiation with gamma-rays or electron beams. Irradiation is almost impossible to detect in tourmalines, and does not, currently, affect the value. Heavily included tourmalines, such as rubellite and Brazilian Paraiba, are sometimes clarity-enhanced. A clarity-enhanced tourmaline (especially the Paraiba variety) is worth much less than a non-treated gem.
Gem and specimen tourmaline is mined chiefly in Brazil and Africa. Other locations which produce gem-quality tourmaline are Sri Lanka and India. Tourmaline is mined in Tanzania, Nigeria, Kenya, Madagascar, Mozambique, Namibia, Afghanistan, India, Sri Lanka, and Malawi.
Tourmaline is also the gem of the eighth anniversary. To learn more about all the wonders of tourmaline, visit the GIA encyclopedia.