Crystals structures of carbonate phases with Mg in Triassic rocks, mineral formation and transitions

Detailed data on carbonate minerals different in magnesium content including their crystal structures were presented in this article. The samples were collected from the formations of the Lower Muschelkalk and the Upper Muschelkalk. X-ray diffraction and electron microprobe analysis were used for carbonate phases determination. The following minerals with different Mg content were identified: low-Mg calcite, high-Mg calcite, proto-dolomite, ordered dolomite and de-huntite. The content of Mg in high-Mg calcite is higher than in low-Mg calcite but lower than that of proto-dolomite. Proto-dolomite is characterized by lower content of Mg than typical for stoichiometric value for dolomite-ordered dolomite. Due to the reduced Mg content in identified huntite, this carbonate phase was named as de-huntite. The research results are significant because they are a source of new data on carbonate phases with different Mg content which build studied Triassic rocks and crystal structures of these minerals.