Niobium

See also:

ChemGlobe: Niobium - Electronic, thermal, and steric data along with a table of isotopes.
ChemicalElements.com: Niobium - Basic information, atomic structure, and isotopes.
EnvironmentalChemistry.com: Niobium - Atomic structure, chemical and physical properties, and table of nuclides.
It's Elemental: Niobium - Basic physical and historical information.
LANL: Niobium - History, sources, properties, and uses.
Lenntech: Niobium - Physical data, chemical properties, and health effects.
USGS Minerals Information: Niobium - Statistics and information on the worldwide supply, demand, and flow of the element (PDF format).
Visual Elements: Niobium - Image, uses, general information, and ionisation energies.
WebElements: Niobium - Extensive information on history, uses, occurrence, compounds, and properties of the element.
Wikipedia: Niobium - Properties of the element, including its history, applications, and characteristics.