San Diego Natural History Museum--Your Nature ConnectionSDNHM Field Guide
[Tourmaline. Collection of the San Diego Natural History Museum.]

Tourmaline

From the Singhalese word, touramalli, meaning "mixed colored stones."

Description and Occurrence

Tourmaline crystal is shaped like a prism and has lengthwise ridges. It exhibits a wide range of colors -- more than any other gemstone -- and is highly prized for that quality. A delightful example of coloration is the watermelon tourmaline; it typically changes from red to green in a concentric color zonation, i.e., from the center out. A colorless variety, achroite, is very rare.

According to the the two most recent classification systems, members of the Tourmaline Group include: buergerite (brown), dravite (brown), elbaite (multicolored to green), schorl (black), and uvite (black, brown, yellow-green). Elbaite can be broken down even further to individual varieties: achroite (colorless), rubellite (red), indicolite (blue), verdelite (green), and tsilaisite (Mn-rich).

Southern California is a world-recognized source of high quality tourmalines. Fine examples of red, pink, blue, green, and watermelon gemstones come from pegmatites in Riverside and San Diego Counties.

Tourmaline has also been found in Sri Lanka; Madagascar; Brazil; near Alamas, Baja California; Afghanistan; Mozambique; and Russia.

Field Notes: Tourmalines may be multi-colored, or show different colors when viewed through different axis (pleochroic). Rubbing or heating the crystal produces a static charge, and the crystal will attract dust particles. Black tourmaline is the most common variety and is often mistaken for another common mineral, hornblende.


Physical Properties

Color Streak Transparency Luster Hardness Cleavage Fracture Specific gravity Crystal form
colorless, all colors white transparent to opaque vitreous 7 to 7.5 poor conchoidal, uneven, brittle 3 to 3.3 hexagonal

Photo: Tourmaline. Collection of the San Diego Natural History Museum
Photo credit: Linda West

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