Tourmaline - 4mm bead bracelet from Brazil

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 sit 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 already known in antiquity in the Mediterranean, he was by the Dutch from Sri Lanka only in 1703 introduced in Western Europe. They named the new gem of a Sinhalese word "Turmali", which means "stone with mixed colors." If gems were used traditionally Rubel left - they were used by artists like talisman, because they would increase creativity of artists. Tourmalines have certain unique features. They are piezo-electric, which means that if a crystal is heated or compressed, different electrical charges are formed at the both ends of the crystal. For example, an electrical potential is created. If an external electrical potential is carried out on the crystal, it vibrates. The minerals are pleochroïsch, which means that the crystal darker color is viewed along the longest axis of the crystal, then seen at right angles to that axis. The four best known and most common 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, extreme slow cooling passage rocks of magma. The other two tourmalines are regularly encountered draviet and fluor-uvite. Draviet is usually brown translucent and can be very large. Fluor-uvite green translucent to opaque. Tourmaline is found in the sand fraction of Dutch Quaternary river sediments. It's include a characteristic ingredient of Maas Zanden. The heavy mineral analysis as in the Netherlands at the Geological Survey took place during the second half of the twentieth century, the mineral is classified among the so-called stable group