Hafnium: historical information
Hafnium was thought to be present in various zirconium minerals many years prior to its discovery, in 1923, which was credited to Dirk Coster and George Charles von Hevesey. It was finally identified in zircon (a zirconium ore) from Norway, by means of X-ray spectroscopic analysis. It was named in honour of the city in which the discovery was made. A number of earlier claims seem less likely.
Most zirconium minerals contain 1 to 3% hafnium and it is their chemical similarity which made their separation difficult. It was originally separated from zirconium by repeated and tedious recrystallization of the double ammonium or potassium fluorides.