is a chemical element that has the symbol Pr and atomic number 59. Praseodymium is a soft, silvery, malleable and ductile metal in the lanthanide group. It is too reactive to be found in native form, and when artificially prepared, it slowly develops a green oxide coating. The element was named for the color of its primary oxide. In 1841, Swedish chemist Carl Gustav Mosander extracted a rare earth oxide residue he called "didymium" from a residue he called "lantana," in turn separted from cerium salts. In 1885, the Austrian chemist baron Carl Auer von Welsbach separated didymium into two salts of different colors, which he named praseodymium and neodymium. The name praseodymium comes from the Greek prasios meaning green, and didymos twin. Praseodymium is frequently misspelled as praseodynium.