Terbium is a metallic chemical element which is classified in the rare earth elements, also known as lanthanides, of the periodic table of elements. It is not found in a pure form in nature, but it can be recovered from an assortment of minerals; China is the source of much of the world's terbium. Like other rare earth elements, terbium is comparatively well distributed across the Earth, but it is not widely used; most consumers do not interact with terbium, although they may own some products with terbium components.
When terbium is isolated, it is silvery gray and relatively soft and easy to work. The element has a crystalline structure, and at least two allotropic forms, meaning the structure of the element can vary when it is in a solid state, depending on the circumstances. On the periodic table of elements, terbium is identified with the symbol Tb, and its atomic number is 65. The element also has a number of isotopes and salts which are used in various applications.
Discovery of the element is credited to Carl Mosander, who was experimenting with minerals from Ytterby, a town in Sweden. Mosander also discovered several other elements, and he was also a teacher of chemistry at the Swedish Museum of Natural History. He discovered terbium in 1843, when he identified an impurity in another element, yttrium. The element was named for Yttrby, an apparently fruitful place for the discovery of new elements since it also lent its name to yttrium, ytterbium, and erbium.
The element is used in some x-ray machines and also in color television tubes. It is also used as a dopant in lasers and semiconductors, and it is alloyed with a number of other metals for various purposes. Various terbium isotopes are used in research. The bulk of the world's terbium comes from the mineral bastnaesite, which is treated with solvents to extract the useful elements it contains.
As is the case with other rare earth elements, terbium is mildly toxic, and therefore people should probably avoid exposure, if possible. Inhalation of dust or fumes from terbium should be avoided with the use of face protection, and radioactive terbium isotopes should be handled in controlled environments under the supervision of people who are familiar with radioactive materials.