Terbium is reasonably stable in air. It is a silver-gray metal, and is malleable, ductile, and soft enough to be cut with a knife. Two crystal modifications exist, with a transformation temperature of 1289°C.
Melting point: 1356 °C Boiling point: 3230 °C
A foil is a thin sheet of pure metal. Given its fragile nature, some foils have protective coatings.