Keywords:MDS DFT Contact angle Interfacial water structure In the first part of this paper, an experimental contact angle study of fresh and Cu 2+ activated sphalerite-ZnS surfaces as well as the covellite-CuS (001) surface is reported describing the increased hydrophobic character of the surface during Cu 2+ activation. In addition to these experimental results, fresh sphalerite-ZnS (110), copper-zinc sulfide-CuZnS 2 (110), villamaninite-CuS 2 (100), and covellite-CuS (001) surfaces were examined using Molecular Dynamics Simulation (MDS). Our MDS results on the behavior of interfacial water at the fresh sphalerite-ZnS (110), copper-zinc sulfide-CuZnS 2 (110), villamaninite-CuS 2 (100), and covellite-CuS (001) surfaces include simulated contact angles, water number density distribution, water dipole orientation, water residence time, and hydrogen-bonding considerations. The copper content at the Cu 2+ activated sphalerite surface seems to account for the increased hydrophobicity as revealed by both experimental and MD simulated contact angle measurements. The relatively greater hydrophobic character developed at the Cu 2+ activated sphalerite surface and at the copper sulfide surfaces has been described by MDS, based on the structure of interfacial water and its dynamic properties.