Magnesium calcite in Muschelkalk limestones of the Polish part of the Germanic Basin

Magnesium calcite, which is usually observed in many natural low-temperature environments, was identified in Triassic limestones of the Polish part of the Germanic Basin. The occurrence of unstable magnesium calcite in Triassic limestones is remarkable. High-Mg calcite was identified in all beds of the Muschelkalk Karchowice Formation: Lower Crinoidea Beds, Lower Biohermal Beds, Upper Crinoidea Beds and Upper Biohermal Beds. The general chemical formulas of magnesium calcite of mentioned unites are: (Ca(0.87–0.80),Mg(0.13–0.20))CO(3), (Ca(0.83–0.75),Mg(0.17–0.25))CO(3), (Ca(0.81),Mg(0.19))CO(3), (Ca(0.78–0.77),Mg(0.22–0.23))CO(3) respectively. This mineral originated probably during the early stage of diagenesis, during compaction of limestones deposited in a warm, shallow marine environment. Some amounts of magnesium come from high-Mg skeletons of marine organisms (such as echinoderms). Diagnenetic processes and the conditions in seawater, especially higher salinity, influence the preservation of high magnesium calcite in the Muschelkalk limestone of the Polish part of the Germanic Basin.