T-XCO2 with Pressure Slider. Temperature-XCO2 diagram for the chemical system CaO-SiO2-MgO-H2O-CO2. H2O and CO2 are treated as mobile components that are free to come and go. The diagram is calculated by "TWQ" software written by Rob Berman and using the internally consistent thermodynamic database of Berman (1991). Move the pressure slider to see how the diagram changes as the pressure changes. Click on the "Show Assemblages" button and mouseover the T-XCO2 diagram to see the mineral assemblages for each region on the T-XCO2 diagram. Mineral assemblages are shown on a CaO-SiO2-MgO ternary assemblage diagram.