Figure 5.15. Identify Reactions using 3-component assemblage diagrams.
The diagram on the left shows the temperature-pressure (T-P) stabilities of 6 minerals (A,B,C,D,E,F) in a 3-component (c1,c2,c3) chemical system. Although this diagram is not based on real experiments, it follows thermodynamic rules and clearly shows equilibrium features of a 3-component system. Follow the instructions for diagram interaction, then click the "Identify Reactions" Button.
Mouse over the T-P diagram on the left to see the compositions of the minerals plotted on the ternary composition diagram on the right. The tie lines connecting minerals that can occur together at equilibrium change when the mouse crosses reaction lines as the T and P are changed. Use this information to identify the Reactions 1 to 5 marked on the T-P diagram.
The minerals that will be in a rock at equilibrium depends not only on the T and P, but also on the chemical composition of the rock. Select a T and P by clicking on the T-P diagram, then mouse over the ternary diagram to indicate a bulk composition with your mouse. The bulk composition is indicated by a white dot and shown quantitatively on the upper right. Furthermore, the equilibrium mineral assemblage for your bulk composition is shown quantitatively on the upper left and graphically with areas proportional to the numerical values determined with the ternary lever rule.
Click on the "Show MAD" button to show the Mineral Assemblage Diagram your selected mineral composition. The MAD will change if the bulk composition is changed. Or click on the ternary diagram to hold a particular bulk composition, click on the change TP button, and mouse over the T-P diagram to see the mineral assemblage changes graphically and numerically when the mouse crosses a reaction line.
