atomic number 27 - a hard ferromagnetic silver-white bivalent or trivalent metallic element; a trace element in plant and animal nutritionmetal, metallic element - any of several chemical elements that are usually shiny solids that conduct heat or electricity and can be formed into sheets etc. cobalt 60 - a radioactive isotope of cobalt with mass number 60; a source of exceptionally intense gamma rays; used in radiation therapy cobaltite - a rare silvery-white mineral; important ore of cobalt smaltite - a gray mineral consisting of cobalt arsenide and nickel; an important source of cobalt and nickel |