Birnessite minerals (layer-type MnO2) produced by bacteria and fungi participate in important biogeochemical processes in oxic and suboxic environments, particularly nutrient and contaminant metal sorption. Birnessite minerals are among the strongest environmental oxidants, contributing to the decomposition of natural organic matter, the oxidative degradation of complex organic pollutants, and the respiration of metal-reducing bacteria in aquatic and terrestrial environments. Despite the importance of biogenic birnessite, several aspects regarding their reactivity remain poorly understood. We hypothesize that biogenic birnessite minerals are distinct in terms of their sorption reactivity and redox reactivity relative to abiotic birnessite minerals due to their occurrence within a biofilm matrix, their large abundance of vacancy sites, and nano-scale dimensions. The objectives of this project are to determine how metal-organic and organic-mineral interactions modify birnessite reactivity, and to determine how mineral properties and structure modify the stability of birnessite against (photo)reductive dissolution. A fundamental understanding of these processes is essential to the development of biogeochemical models that describe aqueous and surface speciation, reactive transport and environmental toxicity. The results from this research have important implications for attenuation of pollution in natural systems; remediation schemes in engineered systems and water treatment; water resource management and water security; and nutrient cycling in terrestrial and marine ecosystems.
This data publication contains scanning electron microscope (SEM) and (scanning) transmission electron microscope ((S)TEM) images as well as electron energy loss spectra (EELS) and Raman spectra of the principal slip surface of carbonate fault mirrors. We analysed a total of eleven samples to investigate the formation mechanisms of fault mirrors in carbonates. The samples were taken as drill cores in Central Greece from two different outcrop locations. The first location, close to Arkitsa, is a large anthropogenic outcrop exposing three large fault planes. The second location is close to Schinos and was also formed by human interaction at the side of a gravel road. The data set contains supplemental material to the publication "Mechanisms of fault mirror formation and fault healing in carbonate rocks" by Ohl et al., (2020). In addition to the electron microscopy images we provide the spectra files of the Raman and EELS measurements for the identification of the carbon species in relation to the principal slip surface. The publication concludes that decarbonation of calcite during fault slip and the subsequent reaction of the decarbonation products produces fault mirror surfaces. Post-seismic hybridization of carbon results in partly-hybridised amorphous carbon and contributes to connecting hanging wall and footwall. In addition, post-seismic carbonation of portlandite produces secondary nano-sized calcite crystals < 50 nm facilitating fault healing.