Ytterbium is a chemical element with symbol Yb and atomic number 70. Its density and melting and boiling points differ from those of the other lanthanides. Once extracted and prepared, ytterbium is somewhat hazardous as an eye and skin irritant. The metal is a fire and explosion hazard. At present, ytterbium is mainly used as a dopant of stainless steel or active laser media, and less often as a gamma ray source.