Page "Refractory metals" Paragraph 1

Most definitions of the term ' refractory metals ' list the extraordinarly high melting point as a key requirement for inclusion.

By one definition, a melting point above is necessary to qualify.

The five elements niobium, molybdenum, tantalum, tungsten and rhenium are included in all definitions, while the wider definition, including all elements with a melting point above, includes a varying number of nine additional elements, titanium, vanadium, chromium, zirconium, hafnium, ruthenium, osmium and iridium.

Transuranium elements ( those above uranium, which are all unstable and not found naturally on earth ) and technetium are never considered to be part of the refractory metals.