Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Praseodymium is a chemical element that has the symbol Pr and atomic number 59. Praseodymium is a soft, silvery, malleable and ductile metal in the lanthanoid group. It is somewhat more resistant to corrosion in air than europium, lanthanum, cerium, or neodymium, but it does develop a green oxide coating that spalls off when exposed to air, exposing more metal to oxidation â€” a centimeter-sized sample of Pr completely oxidizes within a year. For this reason, praseodymium is usually stored under a light mineral oil or sealed in glass.