Hafnium is a ductile metal with a brilliant silver luster. Its properties are considerably influenced by the impurities of zirconium present. Of all the elements, zirconium and hafnium are two of the most difficult to separate. Their chemistry is almost identical, however, the density of zirconium is about half that of hafnium. Very pure hafnium has been produced, with zirconium being the major impurity.
Natural hafnium contains six isotopes.
Hafnium has a total of 40 recognized isotopes and isomers. Such rods are used in nuclear submarines. Hafnium has been successfully alloyed with iron, titanium, niobium, tantalum, and other metals. Finely divided hafnium is pyrophoric and can ionite spontaneously in air. Care should be taken when machining the metal or when handling hot sponge hafnium.