The alteration of todorokite and kutnohorite minerals containing Mn-ions in different oxidation states under the action of fungus Aspergillus niger, one of the most active stone destructors, was studied in vitro. The products of Mn,Ca-bearing minerals alteration were investigated by powder and single crystal X-ray diffraction, optical microscopy, SEM and EDXS methods. The sequence of formation and morphology of the growing oxalate hydrates were analyzed. It was shown that todorokite and kutnohorite alteration under the influence of fungus A. niger is a complex process including solubilization and redox reactions (Mn2+ to Mn3+,4+ oxidation and Mn3+,4+ to Mn2+ reduction), which lead to crystallization of insoluble manganese oxalate hydrates with different amounts of water — biomimetic falottaite, lindbergite. Kutnohorite alteration leads to micogenic Mn3+,4+ -bearing todorokite formation followed by oxalate formation. Biomimetic lindbergite formation was possible from biomimetic falottaite dehydration as well from the alteration of original Mn,Ca-bearing mineral substrates.
Keywords: fungal alteration of rocks and minerals, biomimetic synthesis, manganese oxidation, oxalate crystallization, Aspergillus niger, todorokite, kutnohorite, falottaite, lindbergite
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