hardness 2.5 Vickers hardness 216 MPa Brinell hardness 25 HB MPa CAS registry number 7440-57-5 Most stable isotopes Main article: Isotopes of gold iso NA half-life DM DE ( MeV ) DP 195 Au syn 186.10 d ε 0.227 195 Pt 196 Au syn 6.183 d ε 1.506 196 Pt β