Lutetium is a chemical element with symbol Lu and atomic number 71.
It is a silvery white metal, which resists corrosion in dry, but not in moist air.
It is considered the first element of the 6th-period transition metals (or, on occasion, the last element in the lanthanide series), and is traditionally counted among the rare earths.

https://en.wikipedia.org/wiki/Lutetium