The ratio of the specific component of the surface energy to the total surface energy has previously been related to the hydrophilicity of a surface (Eq. (6)) [28]. At low surface coverage, the sites that are taken up by the probe molecules are the most hydrophilic, and the lower energy sites are more hydrophobic. This is shown in the secondary y-axis of Fig. 7 which gives the degree of hydrophilicity for the galena and quartz samples analysed in this research