Micromorphology and chemical composition of naturally occurring jarosite in coastal floodplain acid sulfate soils from aastern Australia

Recent research has suggested that secondary mineral deposits, such as jarosite, may be useful indicators of the weathering environment of soil landscapes. Although the presence of jarosite is often reported in Acid Sulfate Soils (ASS), little research has been done on its behavior within ASS. It is recognized that jarosite is a ‘store' of acidity, slowing down acid release into the soil and hence reducing acid export. However, the significance of jarosite as a ‘source' of acidity as it breaks down within an ASS has yet to be determined. The purpose of this research is to characterize naturally occurring jarosites in ASS, to provide background data for ongoing research into its properties and impact. Natural jarosite accumulations were extracted by hand from ASS material. Synthetic jarosite was prepared for comparison with natural samples. Samples were analyzed by XRD for identification, chemical content by aqua regia digestion and ICP-OES, crystallinity and micromorphology using analytical scanning electron microscopy. Electrical conductivity, soluble and exchangeable pH, basic cations and metals were measured using a 1:5 jarosite:solution ratio and ICP-OES analysis. Readily available acidity was obtained as titratable actual acidity. The data indicates variability in micromorphology and chemical properties, particularly Na+ and K+ contents and mean crystal diameter. The implications of these results to jarosite formation and stability behavior are discussed.