sulphide minerals

sulphide minerals Minerals in which sulphur is combined with one or more metallic elements are classified as the sulphide minerals. Sulphides are typically metallic grey to brass coloured, and are relatively soft when compared with silicate or oxide minerals. Pyrite, FeS₂, a compound of iron and sulphur, is one of the most common sulphides and is found as a minor component in many rocks. It is also an important accessory mineral in most mineral deposits formed from high-temperature fluids. Its golden metallic colour and common occurrence in gold deposits has lead it to be mistaken for gold; hence its colloquial name of ‘fool's gold’. Other sulphides constitute the most important hosts of several elements that are extracted from ore deposits. For example, sphalerite (zinc sulphide, ZnS) and galena, (lead sulphide, PbS) are the chief ore minerals of zinc and lead, respectively. Other rarer simple sulphides are important sources of cobalt, nickel, copper, molybdenum, cadmium, mercury, antimony, and arsenic. Sulphides in which two metals combine with sulphur are also common and two of these minerals, chalcopyrite (CuFeS₂) and bornite (Cu₅FeS₄), in which copper combines with iron and sulphur, are the most commonly encountered minerals in copper deposits. Minerals in which a metal and sulphur bond with a metalloid element, usually arsenic or antinomy, form a sub-group of the sulphide minerals known as sulphosalts. These are accessory phases, commonly subordinate to the simple sulphides, in many types of mineral deposits. Sulphides are relatively unstable minerals in the surface environment and when exposed to oxidizing groundwaters resulting from mining activities, they degrade, generating high concentrations of acid: hence the term ‘acid mine drainage’.

Bruce W. Mountain