Determination of carbonate minerals with different Mg content in limestone and dolomite by electron microprobe analysis

The results of the identification of carbonate minerals with different magnesium content present in Triassic limestones and dolomites using electron microprobe analysis. The following carbonate phases were identified: low-magnesium calcite, high-magnesium calcite, proto-dolomite, ordered dolomite, and dehuntite in samples from the Lower Muschelkalk formations: Gogolin Unit, Dziewkowice (Terebratula) Unit, and Karchowice Unit, and the Upper Muschelkalk: Tarnowice Unit. They are deposits of the Polish part of the Germanic Basin. The results allowed the calculation of the chemical formulae of the identified carbonate phases. High-Mg calcite has a higher Mg content than low-Mg calcite but lower than typical for proto-dolomite. Proto-dolomite has a lower content of Mg in comparison to the stoichiometric value for dolomite, which is typical for ordered dolomite. The identified huntite phase, because of reduced content of Mg, was named as de-huntite. The diagenetic process – dehuntization – was probably responsible for the reduced Mg content in this phase. The results of the research are the source of new data connected with the mineral composition of Triassic limestones and dolomites of the South-West part of Poland. The data provides complete information on the mineral phases of carbonate rocks of the European Germanic Basin.