Description
A semiprecious gemstone composed of an aluminum borosilicate mineral. Tourmaline occurs in pegmatite deposits, such as found in the Ural Mountains, Bohemia, Germany (Saxony), India, the island of Elba, Norway, England, Greenland, Brazil, Madagascar, and the U.S. (New England, New York, New Jersey, Pennsylvania, California). Tourmalines can be opaque or transparent and range in color from black, dark blue (indicolite), light blue (Brazilian sapphire), brown (dravite), green (Brazilian emerald), red (rubellite) and, though rare, colorless (achroite). Opaque black tourmalines, called schorl, are the most common. Tourmalines form static electricity when they are rubbed or heated. This property makes them useful in pressure gauges, oscillator plates, and other electrical equipment.
Synonyms and Related Terms
schorl (opaque black); tourmalin; turmaline; indicolite (blue); rubellite (pink or red); dravite (brown); achroite (colorless); Brazilian sapphire (light blue); Brazilian emerald (green); Turmalin (Deut, Pol.); turmalina (Esp., Port.); tourmaline (Fr.); toermalijn (Ned.)
| (Na,Ca)(Al,Fe)B3Al3(AlSi2O9)(O,OH,F)4 |
| 7.0 - 7.5 |
| 2.9-3.2 |
| 1.63; 1.66 |
Other Properties
Hexagonal system with small, often rounded, hesgonal crystalline prisms, plates or wedges.
Tourmaline is pleochroic, some forms are dichroic. Fracture = conchoidal or uneven.
Luster = vitreous to resinous. Streak = white Birefringence = high
Hazards and Safety
Tourmaline is piezoelectric (develops a charge when heated) and may attract dust when displayed under a hot light.
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Last updated on: 7/14/2009 2:40:53 PM
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