Metallic chemical element; symbol Fe atomic number 26; (group VIII of the periodic table). Unlike lighter elements, iron cannot be fused to yield energy, and unlike heavier elements it does not yield energy on fission. It exists in four distinct natural crystalline forms. It is a good conductor of heat and electricity. White dwarfs consist almost entirely of iron. Iron is a component of hemoglobin, the oxygen-carrying pigment of the red blood cells of terragen vertebrates.