A gemstone that has a complicated and very varied chemical composition which, rather than internal impurities, accounts for its being found in a wide range of colours. The most common colour is black (schorl), but the transparent colourless variety (achroite) is highly valued. The coloured varieties include blue, red, pink, green, brown, and yellow (with sometimes pink and green in the same crystal), and are known as indicolite, rubellite, dravite, and siberite.
Tourmaline shows strong dichroism, the effect being dependent on the manner of cutting, which is often mixed cut. Some specimens of all colours have fibrous inclusions and, when suitably cut, show chatoyancy (tourmaline cat's-eye). The varieties can be readily distinguished from other stones of similar colours, e.g. yellow zircon and green peridot.
Local misnomers that have been applied to tourmaline include 'Brazilian emerald', 'Brazilian peridot', 'Brazilian chrysolite', 'Brazilian sapphire', 'Ceylon chrysolite', and 'Ceylon peridot'.
From: An Illustrated Dictionary of Jewelry, autor: Harold Newman, publishers: Thames and Hudson