Pyrrhotite Group Minerals
Overview
The pyrrhotite group is defined as all the iron monosulfides of the general formula Fe1-xS (0 < x < 0.125) that possesses a NiAs type substructure. They exhibit a hexagonal close packed structure with [FeS6] and [SFe6] units (Carpenter and Desborough, 1964; Arnold, 1966). This includes troilite (FeS) and the monoclinic and hexagonal pyrrhotites. The pyrrhotites are extremely complex from both a physical and chemical standpoint. They crystallize in the hexagonal or monoclinic systems; troilite (FeS) is hexagonal, whereas pyrrhotite (Fe1-xS) may be monoclinic or hexagonal. These minerals usually appear in massive form, and are commonly found in basic igneous or ultrabasic rocks, in hydrothermal mineral deposits, and in contact-metasomatic sediments. Interest in the
pyrrhotite group arises from their occurrence in metallurgical processes, their properties, and their common occurrence in many types of ore deposits. They are also of importance in terms of geomagnetism monoclinic pyrrhotite being one of the main magnetic minerals in the earth’s crust. Structurally, they are all derivatives of the NiAs structure (Vaughan, 1978; Nesbitt et al., 2002).
Pyrrhotite minerals are abundant in nature, and possesses a dark, brownish rusty colour on their surface. They often occur with pyrite (FeS2), chalcopyrite (CuFeS2), pentlandite ((Fe,Ni)9S8), and magnetite (Fe3O4).
A better understanding of the chemical and physical behaviour of pyrrhotite is of
commercial interest for mineral processing industry, as pyrrhotite is one of the major iron
ores used as feedstock in flash smelting processes for metal extraction (Wang et al.,
2005b).
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