Neodymium is a metal in the lanthanide or rare earth series of elements, which stretches from lanthanum (La) through lutetium (Lu).
The isolation of the element was difficult, as was the case for most of the lanthanides. Their chemical similarity means that they are often found in the same mineral deposit and that they behave similarly when one tries to separate them. In 1841 Mosander separated a rare oxide that he called didymia from another mineral lanthana. In 1885 Auer separated didymia into two other oxides, praseodymia and neodymia, which in turn gave salts of different colors. Pure neodymium metal was not isolated until 1925.
Neodymium metal is one of the most reactive of the lanthanides, so the bright, silvery metal tarnishes rapidly in air forming Nd2O3.
Didymium, composed of Pr2O3 and Nd2O3, is used to make welder's goggles, since this oxide filters out certain wavelengths of light.
Neodymium oxide is also found in photographic filters, as the coloring material in blue-violet glass, and in ceramic capacitors.
Finally, neodymium is used the magnets in headphones.