Transformational Changes in Argillaceous Minerals due to Cyanobacteria

Abstract

The aim of the study was to investigate the transformations of bentonite, illite, kaolin and smectite–zeolite clay at the laboratory experiments under the growth and fossilization of alkaline cyanobacteria Microcoleus Chthonoplastes. Cyanobacteria influenced the chemical properties of studied clays. It had no visible influence on the mineralogy of bentonite and kaolin. Whereas the development of more smectitic layers within the illite matrices in case of illite clay and defect ‘island’ layer in the interlayer space of montmorillonite in smectite–zeolite clay were found. Cyanobacteria affected the properties of iron compounds, which are present in all studied clays as impurities. Both dissolution and precipitation processes of iron compounds were observed. In the experiments with smectite–zeolite and kaolin an increase in magnetic susceptibility and magnetization values connected with the precipitation of Fe in the form of metastable ferrihydrite followed by the formation of goethite were found. This process correlated with the mineralization of organic matter, which plays the role of inhibitor and prevents goethite crystallization during the growth of cyanobacteria. In the case of bentonite a decrease in both magnetic susceptibility and magnetization values connected with oxidation of Fe2+ in the magnetite (maghemite) structure and precipitation of goethite took place. Ferrihydrite is a key mineral in the biogenic cycle of Fe.