Recent electrochemical and x-ray photoelectron spectroscopic (xps) investigations of sulfur enrichment at sulfide mineral surfaces have been reviewed. The nature of the hydrophobic species acquired in the absence of conventional collectors by some sulfides under oxidizing conditions or when treated with hydrosulfide in the presence of oxygen has been discussed. It is concluded that the sulfur-rich surfaces resulting from metal loss in the former case, and sulfur deposition in the latter, are not significantly different in principle. A distribution of sulfur environments is possible, from sulfidic to bulk-elemental in character, depending on the proximity to metal atoms. For low sulfur enrichment, the surface is best regarded as a metal-deficient sulfide. A moderately high level of metal deficiency may result in restructuring to form a polysulfide.