Terbium is the second of the four elements whose names are pieces of Ytterby, that uniquely productive Swedish quarry near Stockholm. The naming of yttrium, terbium, erbium and ytterbium from a single place-name reflects the extraordinary confusion of their discovery, for the rare earths of Ytterby were separated only slowly and in the wrong order more than once, so that the names were reassigned and swapped over the years before settling into their modern form. Terbium has no mythological or alchemical tradition, being a nineteenth-century rare-earth discovery; its identity is geographical, a syllable of a Scandinavian village, and its modern importance lies in the pure green light its compounds emit in fluorescent lamps and screens.
The mix-up between erbium and terbium in particular persisted well into the 1870s, with different chemists using the two names for opposite substances in different countries, until careful comparative work, especially by Marignac, settled the confusion and fixed the modern assignment that holds today. Terbium remains one of the scarcer rare earths in the crust, and its price has tracked the same critical-minerals anxiety now attached to praseodymium and neodymium. Mosander drew both terbium and erbium from a single mineral sample in 1843, a pace of discovery that made him, alongside Auer von Welsbach and Lecoq de Boisbaudran, one of the most productive individual finders in the whole crowded history of the rare earths.