n. [ NL. from Ytterby, in Sweden, where gadolinite is found. Cf. Terbium, Yttrium, Ytterbium. ] (Chem.) A rare earth element of the lanthanide series associated with several other rare elements in the mineral gadolinite from Ytterby in Sweden. Symbol Er. It has atomic number 68 and an atomic weight of 167.26. The pure element is metallic with a bright, silvery luster. It is relatively stable in air, not oxidizing as quickly as some other rare earths. Its salts are rose-colored and give characteristic spectra, and the pink oxide has been added as a colorant in glass and porcelain enamel glazes. Its sesquioxide Er2O3 is called erbia. HCP61 [ 1913 Webster +PJC ]