Erbium (Er) is a silvery, metallic element of the lanthanide series, discovered by C. G. Mosander in Stockholm in 1843; it is named after the Swedish town of Ytterby, where the mineral from which it was first isolated was found. There are six naturally occurring isotopes, and the chief ores are monazite and bastnaesite. Twelve radioactive isotopes have been identified. Soft and malleable, erbium is used in specialized alloys, and erbium oxide is used as a pink colorant for glass. Its most common isotope is 166Er (33.41%).

atomic number 68
relative atomic mass 167.26
relative density 9.045
melting point 1,522°C (2,772°F)
boiling point 2,863°C (5,185°F)