0.31 Mohs hardness 5.0 Vickers hardness 1043 MPa Brinell hardness 700 MPa CAS registry number 7440-48-4 Selected isotopes Main article: Isotopes of cobalt iso NA half-life DM DE ( MeV ) DP 56Co syn 77.27 d ε 4.566 56 Fe 57Co syn 271.79 d ε 0.836 57 Fe 58Co syn 70.86