Neodymium, nee uh DIHM ee uhm (chemical symbol, Nd), is a metallic element belonging to the rare-earth group. Its atomic number (number of protons in its nucleus) is 60. Its relative atomic mass is 144.24. An element's relative atomic mass equals its mass (amount of matter) divided by 1/12 of the mass of carbon 12, the most abundant form of carbon.