Erbium is a member of the lanthanide series, which stretches from lanthanum (La) to lutetium (Lu).
The element was discovered by Carl Gustaf Mosander (1779-1858), who also discovered lanthanum and terbium. He had already found lanthanum in yttria, a mixture of rare earth oxides, and he decided to examine this material further in 1843. Yttria is a mixture of several oxides: ceria (cerium oxide); lanthana (lanthanum oxide); and didymia (a mixture of the oxides of praseodymium and neodymium). Mosander separated these from the yttria, and, in the portion that remained, he discovered two new oxides: a yellow oxide he called erbia and a rose-colored oxide he named terbia. From erbia he found the new element erbium, and the new element terbium came from terbia. In a single experiment Mosander found two as yet undiscovered elements.
In the solid state, the metal has a hexagonal closest packed structure.
Erbium is one of 4 elements (yttrium, terbium, erbium, ytterbium) named for the town of Ytterby in Sweden.
The pure metal is soft and malleable and tarnishes only slowly in air. It can form the oxide erbium(III) oxide
4 Er(s) + 3 O2(g) 2 Er2O3(s)
Most erbium is isolated from the mineral euxerite.
One use of erbium oxide is as a colorant in glass and in photographic filters.