neodymium (nēˌōdĭmˈēəm) [key], metallic chemical element; symbol Nd; at. no. 60; at. wt. 144.242; m.p. about 1,021°C; b.p. about 3,068°C; sp. gr. 7.004 at 20°C; valence +3. Neodymium is a lustrous silver-yellow metal. It is one of the rare-earth metals in the lanthanide series of Group 3 of the periodic table. It exists in two distinct forms (see allotropy); at room temperature it has a hexagonal crystalline structure, but when heated above about 800°C it assumes a face-centered cubic conformation with specific gravity about 6.8. The metal tarnishes in air; the coating formed does not protect the metal from further oxidation, so it must be stored away from contact with air. The oxide (neodymia, Nd2O3) is light blue. The metal is also attacked by water and by acids. Its salts form various red aqueous solutions. Neodymium is present in the minerals monazite and bastnasite. The metal may be prepared from its halides by reduction. Neodymium is one of several metals in an alloy commonly used in cigarette lighter flints. It also is used in powerful permanent magnets and in coloring glasses. The earth didymia is a mixture of the oxides of neodymium and praseodymium. The lenses of goggles used by glassblowers are made with a didymium glass that absorbs the yellow sodium glare of the flame. Neodymium was discovered in 1885 by C. A. von Welsbach who separated Mosander's "didymium" into two components, the earths neodymia and praseodymia.