Tourmaline is a group of cyclic or island-structured silicate minerals characterized by containing boron and may contain various elements such as aluminum, sodium, magnesium, iron, manganese, and lithium. There are 22 mineral species, and the general chemical formula is XY 3Z 6[Si 3O 18](BO 3) 3(OH, F, O) 4. Tourmaline is so named because it carries a charge when heated (i.e., the pyroelectric effect). In the mineral crystallochemical classification, it belongs to the silicates and the cyclosilicate subclass; if the 6-ring [Si 6O 18] composed of the strongest bond [SiO 4] is regarded as an atomic group (island), it can be classified as the nesosilicate subclass. In mineral material science, in the structural-functional classification of mineral raw materials, tourmaline belongs to the one-dimensional structural mineral category and the functional mineral subcategory.