(Gr. neos, new, and didymos, twin) In 1841, Mosander, extracted from cerite a newrose-colored oxide, which he believed contained a new element. He named the elementdidymium, as it was an inseparable twin brother of lanthanum. In 1885 von Welsbachseparated didymium into two new elemental components, neodymia and praseodymia, byrepeated fractionation of ammonium didymium nitrate. While the free metal is in mischmetal, long known and used as a pyrophoric alloy for light flints, the element was notisolated in relatively pure form until 1925. Neodymium is present in misch metal to theextent of about 18%. It is present in the minerals monazite and bastnasite, which areprincipal sources of rare-earth metals.