The tourmaline group includes a number of related species and varieties. They share a common crystal structure but have slightly different chemical compositions. Though tourmaline is a very popular gemstone, the different varieties distinguished by mineralogy are not well known even in the gems business. Both gem dealers and consumers are more familiar with a number of trade names for tourmaline.
The tourmaline varieties defined by mineralogy include: Buergerite and Schorl, iron-containing tourmalines; Dravite, a magnesium tourmaline; Elbaite, the most common tourmaline, containing lithium; Liddicoatite, a calcium tourmaline; and Tsilasite and Uvite, manganese tourmalines.
The better-known trade names include Rubellite, a ruby-red color; Indicolite, referring to any shade of blue tourmaline; Paraiba, the neon blue-green colored by traces of copper; Verdelite, green tourmaline; Watermelon, a tri-color variety; and Chrome Tourmaline, an intense green colored by chromium.
Though Paraiba tourmaline has attracted enormous attention since its discovery in 1989, in fact all the blue tourmalines are quite rare, and high quality specimens are sought after by collectors. Indicolite can range in color from light to deep blue. It is strongly pleochroic, meaning it shows different hues when viewed from different directions. As indicolite appears darker when viewed down the c-axis of the crystal, this must be taken into account when cutting. Poor cutting can result in a loss of transparency and brilliance, especially in darker specimens. Indicolite tourmaline is mainly found in smaller sizes, and gems over 1 carat are especially rare.
Though you will still find names like Rubellite and Indicolite used in the gem trade, they are becoming less common. It is becoming more common to use color names -- red tourmaline, blue tourmaline, etc. -- instead of the trade names. Even Watermelon tourmaline is increasingly referred to as Bi-color or Tri-color tourmaline. This practice matches the test reports issued by well-known gemological labs who use the trade names as secondary names only, if they use them at all.
Indicolite or blue tourmaline is found in Brazil, Sri Lanka, the United States (Maine and California), Madagascar, Nigeria and Mozambique.
- First Published: January-25-2010
- Last Updated: October-08-2010
- © 2005-2013 GemSelect.com all rights reserved.
Reproduction (text or graphics) without the express written consent of GemSelect.com (SETT Company Ltd.) is strictly prohibited.