Construct mineral equilibrium diagrams (at 25° C and 1 atmosphere) for the following mineral assemblage: gibbsite, quartz, kaolinite, halloysite, microcline, muscovite and albite. Use the free energies of formation given in the table below. For each case below, calculate the stability boundaries between all mineral pairs and plot them on a diagram. Then determine which sections of the boundaries are stable and redraft a second diagram with the stable fields labeled. Show all your calculations and annotate your procedure
Case 1. Choose log aK+ / H+ as your abscissa and log aNa+ / H+ as your ordinate for the diagram. Assume the activity of the dissolved silica is fixed at quartz saturation (i.e., assume the solution is in equilibrium with quartz).
Case 2. Choose logaK+ / Na+ as your abscissa and log aH+ as your ordinate for the diagram. Assume the activity of the dissolved silica is fixed at quartz saturation .
Table 1: Free energies of formation in kJ mol-1, at 25° C, 1 atmosphere pressure.
|
Phase |
DG |
| gibbsite | -1154.916 |
| halloysite | -3780.713 |
| kaolinite | -3799.364 |
| quartz | -856.288 |
| muscovite | -5600.670 |
| microcline | -3742.330 |
| albite | -3711.722 |
| water | -237.140 |
| Na+ | -261.900 |
| K+ | -282.490 |
| H4SiO4o | -1308.000 |