Siderit-Magnesit-Mischkristallbildung im system Mg2+-Fe2+-CO 3 2− -Cl 2 2− -H2O

The formation of the solid solution series MgCO₃-FeCO₃ in the system Mg²⁺-Fe²⁺-CO ₃ ^2? -Cl ₂ ^2? -H₂O has been investigstad between 200° C and 500° C. The experimental results show that the composition of any of these carbonates strongly depends on the temperature: At high temperatures mixed crystals rich in MgCO₃ are formed and low temperatures lead to the formation of FeCO₃-rich carbonates. Thus, at 200° C a Fe-poor (Mg-rich) solution is in equilibrium with a Fe-rich carbonate. At temperatures higher than 350° C a Fe-rich (Mg-poor) solution coexists with a Fe-poor (Mg-rich) solid phase; see Fig. 1. At 350° C a solution with a mole fraction^mFe²⁺/(^mFe²⁺+^mMg²⁺) of 0.20 leads to the formation of magnesite very poor in Fe, whereas at 250° C the same solution is in equilibrium with sideroplesit, containing 80 Mol-% FeCO₃, see Figs. 2 and 3. The importance of the experimental results for the formation of deposits of magnesite and siderite is discussed.