Tourmaline (quartz) is a group of minerals, all cyclo silicates. The minerals in this group share a characteristic chemical formula: AX3Y6 (BO3) 3 Si6O18 (O, OH, F) 4. The A may contain calcium or sodium. The X can consist of aluminum, iron, lithium or magnesium. The Y is typically aluminum, but may also be chromium or iron. At the position of A may be some potassium, manganese can be in X and vanadium can be found in Y, but these elements are not common in the formulas of the tourmaline group. Tourmaline is found in pegmatites, metamorfieten, magma tits and alluvial deposits.
Although tourmaline was known already in antiquity in the Mediterranean, he was only in 1703 from Sri Lanka by the Dutch introduced in Western Europe. They named the new gem of a Sinhalese word “Turmali” which means “stone of mixed colors”. If gemstones were used traditionally Rubel left – they were by artists like talisman, because they would increase creativity of artists. Tourmaline have certain unique properties. They are piezo-electric, which means that if a crystal is heated or compressed, different electric charges are formed at the both ends of the crystal. This creates an electrical potential. If an external electrical potential is carried out on the crystal, it vibrates.
The minerals are pleochroïsch, which means that the crystal darker in color is viewed along the longest axis of the crystal, considering than perpendicular to that axis. The four best-known and most abundant tourmaline minerals have different colors and transparencies. ELBAITE is transparent and valuable gemstone. Schorl, which is rich in iron, is the most abundant mineral in the tourmaline group, and is black and opaque. It is mainly formed in pegmatites, the extreme slow cooling gangues of a magma.
The other two tourmalines are regularly encountered draviet and uviet. Draviet is usually brown translucent and may be very large. Uviet green translucent to opaque. Tourmaline is found in the sands of Dutch Quaternary river sediments. Among others it is a characteristic component of Maas Zanden. In the heavy-mineral analysis as in the Netherlands at the Geological Survey during the second half of the twentieth century took place the mineral is classified in the so-called stable group.