Tourmaline is not a single mineral, but a group of related minerals, all having the same basic crystal structure while varying widely in chemical composition, thus color. It is the most multicolored mineral type known, commonly green, red, pink, blue, gray, brown and black, while white, colorless, yellow, orange and purple are less common. Crystals are frequently multicolored, containing two or more distinct colors (Watermelon Tourmaline). With its vitreous luster, colors and durability (7 – 7.5 on the Mohs hardness scale), it is extremely popular among collectors and is a well-known gemstone.
The crystal system for Tourmaline is hexagonal, typically forming elongated prismatic crystals and short, stubby prismatic crystals, both with striations and rounded, triangular cross-sections. Crystals clusters can be columnar and radiating. Other forms include acicular and massive.
For specimen localities for Tourmaline, see the individual Categories for Elbaite, Rubellite and Schorl.