(Gr. prasios, green, and didymos, twin) In 1841 Mosander extracted the rare earthdidymia from lanthana; in 1879, Lecoq de Boisbaudran isolated a new earth, samaria, fromdidymia obtained from the mineral samarskite. Six years later, in 1885, von Welsbachseparated didymia into two others, praseodymia and neodymia, which gave salts of differentcolors. As with other rare earths, compounds of these elements in solution havedistinctive sharp spectral absorption bands or lines, some of which are only a fewAngstroms wide.

The element occurs along with other rare-earth elements in a variety of minerals.Monazite and bastnasite are the two principal commercial sources of the rare-earth metals.It was prepared in relatively pure form in 1931.