Tourmalines are classified as semi-precious stones – any other gemstones besides diamonds, rubies, sapphires, and emeralds. Naturally, it forms a prismatic crystal habitat and vertical striations that parallel the long axis of the crystal. A tourmaline is distinguished by its three-sided prisms; no other common mineral displays this characteristic. Pleochroism is an optical phenomenon in which a gemstone exhibits different colors when observed at different angles. Color is darkest looking down the c-axis of the crystal and lightest when viewing perpendicular to the c-axis. On the Mohs scale
of mineral hardness, a tourmaline measures 7.0 – 7.5. This gemstone is mostly mined in countries Brazil, Afghanistan, Mozambique, Namibia, Nigeria, Pakistan, and Tanzania.
Tourmalines can be found in various colors: red (rubellite), blue (indicolite), green (chrome), yellow (canary) and many others. Black tourmalines, also known as schorl tourmaline, is the most common species of tourmaline and contains trace amounts of sodium and iron. Dravite tourmalines are brown tourmalines and contain trace amounts of sodium and magnesium. Lithium
tourmalines are known as elbaite tourmalines. Tourmalines that are colored a spectacular bright blue to bright green are paraiba tourmalines. Paraiba tourmalines are colored by trace amounts of copper. There are also violet specimens of paraibas; these contain both copper and manganese.
An interesting occurrence, color zoning, produces single crystals that contain two or more different colors of tourmaline. The most popular bicolor tourmaline is “watermelon tourmaline.” Furthermore, some tourmalines are also described as chatoyant – minerals that exhibit a “cat’s eye.” Chatoyant tourmalines are properly cut as a cabochon.
Common treatments perforned on tourmaline stones are heat and irradiation. Both these treatments can lighten an undesirable color. Imitation tourmalines are stones which appear physically similar however differ in chemical composition. Tourmaline imitations are usually not gem-quality therefore solely utilized for industrial purposes.