"To the same class of fiery red stones belong the 'lychnis' [probably tourmaline] so called form the kindling of lamps, because at that time it is exceptionally beautiful...I find that there are other varieties as well, one of which has a purple and the other a scarlet sheen. These when heated in the sun or being rubbed between the fingers, are said to attract straws and papyrus fibers."
-- Pliny the Elder (AD 23-79)
Tourmaline is a complex boro-silicate of aluminium and various other metals - its scientific formula consists of fifth characters. It contains long, prismatic crystals that have a rounded triangular shape in cross section, with strong striations along its length.
Because of its variety of colors, tourmaline is easily confused with many precious gems. This relatively inexpensive stone has the greatest color range of all the gemstones - colorless, pink, green, blue, brown, and all kinds of intermediate shades. There is also an attractive and unusual purplish color known as "Siberite" - a name reserved for crystal found in the Russian Ural Mountains.
Parti-colored stones of two or these colors are quite common - for example, pink at one end, colorless in the center, and green at the other end of a crystal or faceted stone. Some crystals, when cut across their width, will show a pink center surrounded by a green border, looking very much like a slice of watermelon. This "Watermelon Tourmaline" comes mainly form Brazil.
Brazil is also home to an attractive, intense emerald green stone - popularly known as "Brazilian Emrald". Known, too, by the name chrome green tourmaline, this could be confused wit genuine emerald by the general public. At one time, this variety of green tourmaline was consecrated and set in episcopal rings.
A cross-section of other tourmaline crystals will reveal a green center surrounded by a pink border. These come from gem-bearing gravels and mines in parts of Africa, such as Mozambique, Angola, Tanzania and Zambia.
The Dutch colonists, nothing the magnetic quality of tourmaline when it was heated, used long, unfashioned crystal of the gem to draw ash from their tobacco pipes. For This reason they named the stone ashentrekker - Ash Puller.
Although tourmaline has been used in the making of jewelry in the Middle and Far East for centuries, it was not until the Dutch introduced the stone into Europe, around the year 1700, that tourmaline became widely known and admired. From about 1750 onward, the stone became highly fashionable as a gemstone. As its popularity increased, the common name was changed from ashentrekker to the Sinhalese turmali.
When faces are present on both ends of a natural crystal they can be seen to have developed with different orientations and do not correspond. This phenomenon is known as hemimorphism, and gives the stone certain electrical properties. Tourmaline, for example, is pyroelectric, developing an electrical charge when heated. This makes it ideal for using in thermometers. Tourmaline also exhibits piezoelecticity, when its crystal are placed under stress. This property is used in underwater detection equipment and in depth and pressure gauges. Another feature of the gem is that, when slices of tourmaline are cut from a prism face, along the length of a crystal, they have the ability to polarize light.