EnvironmentalChemistry.com: Erbium EnvironmentalChemistry.com: Erbium: Atomic structure, chemical and physical properties, and table of nuclides. (Erbium) http://environmentalchemistry.com/yogi/periodic/Er.html
ChemGlobe: Erbium ChemGlobe: Erbium: Electronic, thermal, and steric data along with an isotope table. (Erbium) http://www.vcs.ethz.ch/chemglobe/ptoe/_/68.html
WebElements: Erbium WebElements: Erbium: Extensive information on history, uses, occurrence, compounds, and properties. (Erbium) http://www.webelements.com/webelements/elements/text/Er/key.html
Lenntech: Erbium Lenntech: Erbium: Physical data, chemical properties, health and environmental effects. (Erbium) http://www.lenntech.com/Periodic-chart-elements/Er-en.htm
Erbium Erbium: Includes the history of the element, and a data sheet. (Erbium) http://www.scescape.net/~woods/elements/erbium.html