Praseodymium

Praseodymium is a soft, silvery rare-earth metal that slowly forms a green crust in air. Carl Auer von Welsbach separated it in 1885 from didymium, a substance thought to be one element that turned out to be two: praseodymium and neodymium. Its name means green twin.

It is mined with other rare earths, mostly in China. Praseodymium is often mixed with neodymium in strong rare-earth magnets, like the neodymium magnets in speakers and electric motors. It colors glass and ceramic glazes yellow-green, and goes into the protective goggles worn by glassblowers and welders. It also strengthens some alloys used in aircraft engines.