|Atomic mass||158.9254 amu|
Terbium, discovered in 1843, is a soft, ductile, malleable and silvery element of the lanthanide series.
Terbium is extremely reactive when exposed to air or oxygen and must be kept in an inert atmosphere.
Terbium is a rare-earth metal occurring in low concentration in monazite sand, which is a mixture of phosphate of calcium, thorium, cerium, and most of the other rare-earths. This sand is often 50% rare-earth by mass and about 0.03% terbium. Other sources of terbium are oxide mixtures found in xenotime and euxenite. Such oxide mixtures often contain up to 1% terbium.
Terbium is used in special lasers and as a dopant in solid-state devices.