A sample of a 1.7 kg (3.7 lb) hafnium crystal bar, made by the van Arkel-de Boer process. Hafnium is a lustrous, silvery gray, tetravalent transition metal that chemically resembles zirconium and is found in zirconium minerals. Its existence was predicted by Dmitri Mendeleev in 1869. Industrially, it is used in filaments and electrodes.Photo: Alchemist-hp