Lutetium is a chemical element with the symbol Lu and atomic number 71. It is a silvery white metal that is relatively rare in nature. LUTETIUM is the last element in the lanthanide series, and it is traditionally counted among the rare earth elements. It is also sometimes considered the first element of the 6th-period transition metals. LUTETIUM has few applications, but it is used in some catalysts, as well as in the production of synthetic gemstones.