1. Data from chemical analysis of fresh and especially sea water as well as natural hydrothermal solutions from active hydrothermal fields and from fluid inclusions clearly show that potassium and sodium are the main components of such
solutions. These components have a big, sometimes decisive influence on water-rock interaction processes.
2. Thermodynamic calculations and experimental data show that in the area of low pH (<5) potassium and sodium aluminosilicates does not form, independently of particular solution composition. At low temperature (below 250 oC) kaolinite (dikkite) and sometimes nakrite clearly predominate. As temperature rise these minerals are replaced by pyrophyllite. Further raise of temperature cause a pyrophyllite replacement by andalusite, distane or sillimanite, depending on pressure.
3. In moderate pH area (about 5-8) the most possible minerals are potassium and sodium micas -- muscovite and paragonite correspondingly. At the same time for paragonite crystallization Na+ must be present in predominant or even overwhelming amount over K+.
Moreover, according to experimental data by G. Popov, paragonite formation is simply impossible at temperatures below 350 oC even if Na+/K+ exceeds 10. Probably, we must consider that paragonite crystallization is possible, however at high values of sodium-potassium ratio. At higher temperatures this ration can be lower to make paragonite crystallization possible.
4. In high pH area (>8) K-feldspar and albite dominate. Thermodynamical calculations and experimental data by Orwill, Baletsky, Zyryanov and others show that for replacement of KFS by albite the Na+ predominance over K+ is also necessary, but not as big as for muscovite replacement by paragonite. As temperature increase the Na+/K+ ratio decrease.
5. These data lead to a preliminary explanation of long-known phenomenon that in a water-rock system at a temperature from 25 oC to 500 oC sodium concentrates mostly in liquid phase and potassium in solid phases. Moreover, it is easy to imagine a situation that sodium-potassium solution during increase of pH and decrease of temperature -- and these parameters are related -- will deposit first muscovite and then albite. The results of the similar processes can sometimes be observed even within a single mineral grain.
Baletsky, V.S., Geochemistry 3, 332-338 (1971).
Orwill, P.M., A.J.S. 261, 201-137 (1963).