ChemicalElements.com: Erbium
Basic information, atomic structure, and isotopes.
EnvironmentalChemistry.com: Erbium
Atomic structure, chemical and physical properties, and table of nuclides.
Erbium
Includes the history of the element, and a data sheet.
It's Elemental: Erbium
Basic physical and historical information.
Lenntech: Erbium
Physical data, chemical properties, health and environmental effects.
Visual Elements: Erbium
Image, physical information, key isotopes, and ionisation energies.
WebElements: Erbium
Extensive information on history, uses, occurrence, compounds, and properties.
Wikipedia: Erbium
Properties of the element, including its history, applications, and characteristics.