Emporia State University
 Image taken from Gallery of Gemstones. |
The tourmaline group of minerals has a number of varieties, with the most common being indicolite (blue), rubellite (pink to red), schorl (black, and commonly used in mourning jewelry), and verdelite (green in all shades). Common properties include a hardness of 7-7.5, specific gravity of 2.82-3.32, and uneven to small conchoidal fracture, with brittle tenacity. |  Pink Tourmaline. Image taken from Gallery of Gemstones. |
 Bi-colored Tourmaline. Image taken from Gem Hut. | Bi-colored tourmaline crystals are common and the stones with a red core and green "skin" are called watermelon tourmaline. The crystal system is trigonal-hexagonal, which is reflected in the common prismatic crystal forms with triangular or hexagonal cross sections. It is doubly refractive with refractive indices of 1.614 and 1.666. Although the fluorescence is weak to none, pleochroism is detected in the different varieties. |
| Tourmaline cat's eye may be found in both pink and green varieties. Gem tourmaline deposits are found in pegmatites. Tourmaline is an October birthstone. Visit this Smithsonian site for a stunning image of natural tourmaline crystals, http://www.nmnh.si.edu/minsci/images/gallery/27.htm.
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 Pink Cat's Eye Tourmaline. Image taken from Gem Hut. |
 Indicolite Tourmaline, heated to improve color. Image taken from Gem Hut. |
Tourmaline is pyro- and piezo-electric, that is when rubbed or by heating and cooling and applying pressure, the crystal will become electrically charged. It was known in times past as the "ash puller," because it was used to pull ash from meerschaum tobacco pipes. This attraction for particles and dust means it must be cleaned more often than other gems. Synthetic tourmaline is used for industrial, not gem, purposes. |  Indicolite Tourmaline, not treated. Image taken from Gem Hut. |
Return to the Syllabus or choose another gemstone below.
| Alexandrite | Amber | Amethyst | Chalcedony | Diamond | Emerald |
| Garnet | Jade | Malachite | Opal | Pearl | Peridot |
| Ruby | Sapphire | Tanzanite | Topaz | Tourmaline | Turquoise |
This page originates from the Earth Science department for the use and benefit of students enrolled at Emporia State University. For more information contact the course instructor, S. W. Aber, e-mail: saber@emporia.edu Thanks for visiting! Webpage created: November 15, 2000; last update: January 7, 2007.
Copyright 1999-2007 Susan Ward Aber. All rights reserved.