Mohs hardness 4.0 Vickers hardness 638 MPa Brinell hardness 700 MPa CAS registry number 7440-02-0 Most stable isotopes Main article: Isotopes of nickel iso N.A. half-life DM DE ( MeV ) DP 56 Ni syn 6.075 d ŠÅ - 56 Co ŠÃ 0.158, 0.811 - 58 Ni 68.077% 58 Ni is