Discovered by Mosander in 1843. Terbium is a member of the lanthanide or "rare earth" group of elements. It is found in cerite, gadolinite, and other minerals along with other rare earths. It is recovered commercially from monazite in which it is present to the extent of 0.03%, from xenotime, and from euxenite, a complex oxide containing 1% or more of terbia.
Sodium terbium borate is used in solid-state devices. It can be used with ZrO2 as a crystal stabilizer of fuel cells which operate at elevated temperature. Few other uses have been found.