Sequential dehydration of the phosphate–sulfate association from Gura Dobrogei Cave, Dobrogea, Romania

Abstract. A rich association of primary guano minerals, including taranakite, hydroxylapatite, brushite and gypsum with relicts illite, kaolinite, alpha (low) quartz calcite, was identified in the fossil bat deposit from Gura Dobrogei Cave, Dobrogea County, Romania. Gypsum Ca phosphates developed preferentially on carbonate bedrock or fallen blocks mass, whereas taranakite clay-rich, detritic sequences. The mineral species cave were characterized by optical methods, scanning electron microscopy, X-ray powder diffraction, Fourier-transform infrared inductively coupled plasma–atomic emission spectrometry analysis. Chemically induced local dehydration low temperatures (up to 100 ∘C even lower) critically depending exothermal reactions prompted formation a secondary association, consisting francoanellite, bassanite monetite. Topotactic substitutions observed cases francoanellite monetite brushite. In its turn, ardealite partially replaced bassanite. sequential process seems driven degradation organic matter microbial action also, presumably, other exothermic at scale (e.g., oxidation ammonia, allogenic pyrite compounds).