The solubility of a low-Fe clinochlore between 25 and 175 °C and Pv = PH2O
Aja, Stephen U.; Small, Joe S.
European Journal of Mineralogy Volume 11 Number 5 (1999), p. 829 - 842
published: Sep 30, 1999
manuscript accepted: Apr 6, 1999
manuscript received: Apr 29, 1998
ArtNo. ESP147051105004, Price: 29.00 €
Abstract Solid mixtures of kaolinite-chlorite (± quartz) and/or chlorite-gibbsite have been equilibrated in aqueous 1.0 M NaCl, 0.001 and 0.005 M MgCl2 solutions at 25, 125 and 175 °C and saturated vapor pressures. Reversibility of fluid-mineral equilibria was demonstrated by approaching final solution compositions from high and low log a1/2 Mg 2+/aH+ and from silica under- and super-saturation. At the end of the experiments, the solutions were separated using immiscible displacement techniques. The chlorite-kaolinite equilibrium suggests a temperature-dependent reaction mechanism which may partly reflect changes in speciation of aqueous ions as well as variations in reaction kinetics. Log K for the chlorite-kaolinite reactions have been calculated to be 52.43 ± 7.50, 62.33 ± 6.89 and 79.06 ± 2.60 at 25, 125 and 175 °C, respectively. Acomparison of the measured Mg/H activity ratios at 25 °C with values predicted for (end-member) clinochlore-kaolinite equilibria indicates that the experimentally measured assemblage is more stable; this suggests a large value of Gibbs energy of mixing (ΔG°mix) for chlorite solid solutions.