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Resumen:
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The magnesium and iron sulfate mineral slavikite has been found in Pastora Mine, Aliseda, Cáceres, Spain, in association with a number of other sulfate minerals such as alunogen, fibroferrite and tschermigite. Remarkably, slavikite is the major phase on some walls of Pastora Mine. To the best of our knowledge, this is the first reported occurrence of slavikite in Spain. Here, we present a mineralogical characterisation of the slavikite found in Pastora Mine using X-ray powder diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, electron probe micro-analysis and thermogravimetry. This characterisation also includes an analysis of the morphology of slavikite crystals based on the Bravais-Friedel-Donnay-Harker method, and the determination of the following slavikite formula from microprobe analyses and thermogravimetric data: Mg4Fe10(SO4)15(OH)8·13(H2O). Finally, we discuss the possible formation conditions of slavikite in Pastora Mine on the basis of available geological information and water analyses. We hypothesise that the presence of slavikite as major sulfate phase in some sites of Pastora Mine is partially the result of a process of mineral enrichment in which the moderate solubility of slavikite and wet and dry weathering cycles play a major role.
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