Terbium

Description: Terbium is a relatively stable element in air. It is a silver-gray, malleable and ductile metal that is soft enough to be cut by knife. There are two crystal modifications with transformation temperatures of 1289°C. There are 21 recognized isotopes with atomic masses ranging from 145 to 165. The oxide is a dark maroon or chocolate color.

Source: Terbium was isolated only recently along with the development of ion-exchange techniques for separating rare-earth elements. It can be produced by reducing anhydrous chloride or fluoride with calcium metal in a tantalum crucible.