Mohs hardness 3.0 Vickers hardness 369 MPa Brinell hardness 874 MPa CAS registry number 7440-50-8 Most stable isotopes Main article: Isotopes of copper iso NA half-life DM DE ( MeV ) DP 63 Cu 69.15% 63 Cu is stable with 34 neutrons 65 Cu 30.85% 65 Cu is stable with 36