Dysprosium, chemical element, symbol Dy; for physical constants see Periodic Table. Dysprosium, a metallic element, was discovered by Lecoq de Boisbaudran in 1886. The most important natural source of the element is the mineral monazite. It is a member of the lanthanide series of elements and is prepared by the reduction of the trifluoride with calcium metal. Ion-exchange and solvent extraction techniques have led to much easier isolation of the so-called “rare-earth” elements. Dysprosium and its compounds are used in nuclear control rods, laser materials, and as a source of infrared radiation, as well as special glasses and enamels.