Abstract is: Yttrium is a chemical element with the symbol Y and atomic number 39. It is a silvery-metallic transition metal chemically similar to the lanthanides and has often been classified as a "rare-earth element". Yttrium is almost always found in combination with lanthanide elements in rare-earth minerals, and is never found in nature as a free element. 89Y is the only stable isotope, and the only isotope found in the Earth's crust. The most important uses of yttrium are LEDs and phosphors, particularly the red phosphors in television set cathode ray tube displays. Yttrium is also used in the production of electrodes, electrolytes, electronic filters, lasers, superconductors, various medical applications, and tracing various materials to enhance their properties. Yttrium has no known biological role. Exposure to yttrium compounds can cause lung disease in humans. The element is named after ytterbite, a mineral first identified in 1787 by the chemist Carl Axel Arrhenius. He named the mineral after the village of Ytterby, in Sweden, where it had been discovered. When one of the chemicals in ytterbite was later found to be the previously unidentified element, yttrium, the element was then named after the mineral.