Figure 5.11. NaAlSiO4-SiO2 Stability Diagram.
The diagram on the left shows the temperature-pressure (T-P) stability of mineral assemblages that include Nepheline (Ne), Albite (Ab), Jadeite (Jd) and Quartz (Qz) in the 2-component system NaAlSiO4-SiO2. Select a chemical composition with the slider on the right, then mouse over the T-P diagram to see what minerals will be present and in what proportion for that composition at different temperatures and pressures. The mineral proportions are determined by the lever rule.
The two minerals that are in equilibrium depend on the chemical composition, as well as the T and P. Click on the "Show MAD" button to show the Mineral Assemblage Diagrams for this system. Use the slider to change the bulk composition and the MAD will change when the bulk composition crosses the Jd or Ab composition. Notice that for many compositions, only one of the two chemical reactions is possible. Notice also that when two minerals are reacting to form a third mineral, one of the reactant minerals is completely consumed. Which reactant mineral is consumed depends on the bulk composition relative to the proportion of each reactant mineral used to make the product mineral
The Jd = Ne + Ab reaction is based on based on Newton and Kennedy (1968). The Jd + Qz = Ab reaction is based on the thermodynamic model dataset SPaC (version 2015) developed originally by Spear and Cheney (1989).
