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The name tourmaline includes an entire mineralogical family; chemically tourmaline is a mixture of aluminiferous, bouriferous and fluoriferous silicates of various metals. The name derives from the Sinhalese word "turmali" which means "mixed pack"; this refers to the multitude of colors that characterize this mineral. Tourmaline varieties are: acroite (colorless); indicolite (blue-blue color); rubellite (rosy color, ruby red); dravite (brown color); schorl (black color); elbaite (polychrome); uvite (brown, light brown-brown color); green, olive-green, pistachio-green, dark green tourmaline; yellowish, yellow, golden-yellow, yellow-orange tourmaline.
It is one of the most common mineral in the rocks of various types and in particular of the granites, gneis and mica schists, in which however the black variety is generally found. Transparent tourmalines of various colors are generally found in druses and geodes of the pegmatites. The coloring principles are not well defined and undoubtedly the various colors are related to the nature of the oxides that are part of the chemical composition of these minerals. The coloring is uniform but there are often variously colored areas, with gradual passage and sometimes with a clear detachment between the different colors. In fact, tourmalines are characterized by pleochroism visible even with the naked eye: a very intense color is observed in the direction of the main crystallographic axis, while it appears lighter if it is observed through the faces of the prism.
Tourmalines crystallize in the rhombohedral system and the crystals have an elongated prismatic dress with three, six or nine sides. One end of the prism is almost always implanted in the mother rock; otherwise they are often hemiform, so the two ends have different conformations. The crystals show numerous streaks, often very accentuated and parallel to the direction of the optical axis. The sizes of the crystals are varied and often relevant.
Important deposits in which tourmalines are extracted are located in Brazil, Kenya, Tanzania, Madagascar, Mozambique, Sri Lanka, Russia and in the USA. The most beautiful polychrome tourmalines come especially from Madagascar and from Brazil.