Lutetium is a chemical element with the symbol Lu and atomic number 71. It belongs to the lanthanide series and is a silvery-white metal that is relatively stable in air. Lutetium is one of the rarest and heaviest of the lanthanides, and it is primarily used in various applications, including catalysts in petroleum refining and in certain types of lasers. This element was discovered in 1907 by Georges Urbain, who isolated it from a mineral called monazite. Lutetium has a high melting point and is known for its ability to absorb neutrons, making it useful in nuclear applications. Its compounds are also used in the production of phosphors for LEDs and other lighting technologies.