Terbium

Terbium is a soft, silvery-white lanthanide metal. It does not occur naturally as a pure element: it is mixed with other rare-earth elements in minerals such as monazite and xenotime. Some of the richest commercial sources are ion-adsorption clays in southern China. To obtain terbium, processors dissolve crushed mineral material, separate the rare-earth elements—often using ion-exchange resins—and then reduce a purified terbium compound to the metal. Terbium ions glow bright green, so terbium compounds are used in phosphors for lighting and screens. Terbium also helps make Terfenol-D, an alloy that changes shape in a magnetic field. This unusual effect makes the alloy useful in devices such as sensors, actuators, and sonar equipment.