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Tourmaline occurs in a wide range of colors. It is one of the most favored gemstones for collectors due to its incredible variety of colors and the beauty of its crystals. Most tourmalines are known by the variety name following their color: Rubellite (pink to red but also brownish, purplish or orangey), Verdelite (yellowish green to bluish green), Indicolite (violetish to greenish blue), Dravite (yellow to brown), Achroite (colorless), Schorl (black), Paraiba (electric blue typical from Paraiba area in Brazil), Chrome Tourmaline (intense green).
Highly saturated tourmalines with fine clarity will be highly priced with some exceptions, such as for Rubellite which is usually very included. Burma (Myanmar) is known for its fine tourmalines, which are mined in Mogok (most varieties), the Molo area near Momeik (Schorl and Rubellite) and the Shan and Kayin states (green tourmaline). But most of the tourmaline commonly in the market is now coming from Brazil and Madagascar.
Tourmaline forms as a trigonal crystal in a variety of geological settings; as an associated mineral in metamorphic rocks as gneiss or schist, as long prisms in granitic pegmatite usually with a feldspar matrix, or as single crystals after alteration of the pegmatite resulting, for example, in kaolinisation.
In this granite pegmatite it occurs in the immediate vicinity in the enclosing host rocks. Pegmatite tourmaline is commonly black and is associated with quartz and feldspar. The light colored gem tourmalines are much rarer, usually occurring in pegmatite core zones.
Other occurrences for tourmaline are in hydrothermal veins where heated mineral bearing liquids or gases from deep igneous sources later cooled and crystallized along rock fractures, in granites due to late stage alteration of micas and feldspars by boron containing fluids, and by boron metasomatism in contact and regionally metamorphosed rocks.
Some tourmaline bearing mica schist may have formed by regional metamorphism of argillaceous sediments containing evaporate borates. Because of tourmaline's relatively high hardness and specific gravity, it is often found in elluvial and alluvial deposits as for example in the gravels of Mogok in Burma or in those of Sri Lanka.
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