Investigations of the heterogeneous formation of ikaite and of the ikaite transformation as important processes for the genesis of stable calcium carbonate minerals

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Ikaite (CaCO3x6H2O) is an important calcium carbonate mineral in the cold regions of Earth. Numerous occurrences of ikaite and its pseudomorphs are documenting the significant role of the mineral as a substantial part of the polar carbon cycle. Despite its widespread occurrence, conditions of formation and stability of ikaite are poorly known. Especially, knowledge of the heterogeneous nucleation and transformation of ikaite is missing. This impedes a reliable assessment of the conditions of formation and stability of this mineral in nature. Previous work showed that quartz and mica surfaces enlarge the supersaturation range of ikaite formation at T = 0 °C significantly if compared to homogeneous conditions. Presence or absence of mineral surfaces, therefore, is a fundamentally important criterion for ikaite formation. It is still unknown, however, to which extent the effects of mineral surfaces are significant for ikaite nucleation at temperatures above 0 °C. Additionally, the effects of increased temperature on transformation of ikaite into more stable anhydrous calcium carbonates in presence of mineral surfaces are unknown. Knowledge of heterogeneous nucleation and transformation of ikaite at temperatures above the freezing point of water, however, are of immense importance for a correct evaluation of the applicability of this mineral as an indicator of cold temperatures. Moreover, knowledge of heterogeneous formation and transformation of ikaite at T > 0 °C can contribute to a significantly better understanding of the various formation paths of anhydrous CaCO3 polymorphs in the cold regions of Earth. Aim of the project, therefore, is investigating the formation and transformation process of ikaite in presence of mineral surfaces at T > 0 °C. Based on the successfully conducted cryo-mixed-batch-reactor (CMBR) experiments on heterogeneous nucleation of ikaite at T = 0 °C, we will investigate the formation conditions at T > 0 °C in the presence of quartz and mica. Furthermore, knowledge of the stability and the transformation process of ikaite in the presence of these mineral surfaces will be obtained. For these purposes, the impact of the substrates on the nucleation and transformation processes will be investigated using phase analysis (XRD) and microscopy (cryo-SEM and cryo-AFM) additionally to the CMBR-experiments.