Morphology of Pyrite in Alum Shale, Oslo, Norway

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Abstract
The XRD of a stone-sawn pyrite lump shows that the mineral is pure, apart from some inclusions of quartz. EDX-analysis, carried out in connection with the SEM, also confirms the XRD findings in that pyrite is the only sulphide of importance in these shales. Three major morphological forms of pyrite were observed and studied. SEM and HLS clearly showed that framboidal pyrite is an important morphological form in these shales. Samples of pyrite and alum shale were collected from excavations under the Norwegian Parliament (Stortinget) in connection with a garage construction in 1987. The weathering of these shales involves the oxidation of the pyrite which in turn produces ferric ions and acidities. The ferric ions catalyse the oxidation of more pyrite producing more acidity, which accelerates the weathering of the shales. Because of its large surface area, the oxidation rate of framboidal pyrite has been shown by many workers to be greater than that of other forms.