Impact of composition and local, bulk and surface structure of fibrous carbonates on their fabric and morphology

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Although carbonates containing radiaxial fibrous and/or fasicular optical calcite cements are considered to be one of the best proxies for the geochemistry of ancient oceans, their formation and the structural origin of their unusual properties are only poorly understood. Therefore, in this project bulk and surface structure and composition of fibrous radiaxial calcites will be studied together with seed formation and growth conditions. Using crystallographic techniques such as the analysis of the crystal structure, globally and space resolved, and the analysis of the composition and structure of surfaces, a most complete relation of structure, composition and morphology will be obtained. The comparison of natural and synthetic (experimental) samples should allow for a rational understanding of processes involved. In crystal growth experiments also the question of rhythmic growth will be addressed. In particular the influence of changing composition of mother liquor on the morphology and composition of the crystal is of interest. All products will undergo crystallographic characterization. In addition, the influence of organic molecules such as amino acids, sugars, lignin etc. on the growth process will be studied considering micrite formation conditions. For an understanding of processes in atomic resolution, from model systems of large calcite crystals interacting with these organics, the structure of the surface including the organic add-layer will be analyzed using grazing incidence X-ray diffraction (GIXRD) and atomic force microscopy (AFM) experiments.