MINERALS/Sulphides 577 Figure Parent and derivative crystal structures in the sulphide minerals (A) The sphalerite (ZnS) structure with the chalcopyrite (CuFeS2) and stannite (Cu2FeSnS4) structures (B) The sphalerite and chalcopyrite unit cells with octahedra of metals outlined, within which may be an additional metal ion in the minerals talnakhite (Cu9Fe8S16), mooihoekite (Cu9Fe9S16), and haycockite (Cu4Fe5S8); the arrangement of additional occupied metal sites is as shown (also shown are the dimensions of the parent sphalerite cell in (A)) (C) The niccolite unit cell of high temperature FeS, which has vacancies in place of iron atoms in monoclinic pyrrhotite (Fe7S8) that are ordered as shown, with vacancies represented by squares (and only iron atom layers shown); also shown in a projection onto the basal plane are the distortions that occur in the troilite modification of FeS Adapted from Institute of Materials, Minerals and Mining, Sulphite Deposits their origin and Processing, ed P Gray, 1990 Table Magnetic and electrical properties of some major sulphide minerals Mineral species Magnetic properties Electrical properties Sphalerite (ZnS) ‘Iron sphalerite’ (Zn,Fe)S Galena (PbS) Pyrite (FeS2) Cattierite (CoS2) Chalcopyrite (CuFeS2) Covellite (CuS) (monoclinic) Pyrrhotite (Fe7S8) Carrollite (CuCo2S4) Pentlandite (Ni,Fe)9S8 diamagnetic paramagnetic diamagnetic diamagnetic ferromagnetic (Tc 110 K) antiferromagnetic (TN 823 K) diamagnetic(?) ferrimagnetic (Tc 573 K) Pauli paramagnetic Pauli paramagnetic insulator (Eg$3.7 eV) semiconductor (Eg$0.5 eV for ca 12 at.% Fe) semiconductor (n and p type, Eg$0.41 eV) semiconductor (n and p type, Eg$0.9 eV) metallic semiconductor (n type, Eg$0.5 eV) metallic metallic metallic metallic Eg, band or ‘energy’ gap; Tc, Curie temperature; TN, Ne`el temperature indicates, whereas such non-transition-metal sulphides as sphalerite and galena are diamagnetic; diamagnetism is also exhibited by pyrite and marcasite (the other FeS2 polymorph) Substitution of iron for zinc in sphalerite leads to paramagnetic behaviour, and many transition-metal sulphides show various forms of magnetic ordering at lower temperatures, including antiferromagnetism (e.g chalcopyrite), ferromagnetism (e.g cattierite), and ferrimagnetism (e.g monoclinic pyrrhotite, although hexagonal pyrrhotites are antiferromagnetic) Other transition-metal sulphides that are metallic conductors exhibit the weak temperatureindependent paramagnetism known as Pauli paramagnetism Metallic conductivity occurs in many sulphides of diverse magnetic character, and, in addition, numerous sulphides are semiconductors and a smaller number (e.g pure sphalerite) are insulators Among semiconducting sulphides, both intrinsic and impurity (or extrinsic) conduction mechanisms occur, and conduction both via electrons (n-type) and via holes (p-type) is common Such variations are often a consequence of the presence of very minor impurities or of