QUARTZ SOLUBILITY AT LOW TEMPERATURES

Abstract

New quartz solubility measurements in pure water that approached equilibrium from undersaturation at 21, 50, 74, and 96°C were combined with critically selected quartz solubility data from the literature to create a revised solubility function for the temperature range 0-300°C: log m = -1107.12(+/-10.77)/T - 0.0254(+/-0.0247) where m is the modal solubility and T is in Kelvins. This function predicts 11.0 +/- 1.1 ppm as the solubility of quartz at 25°C. All uncertainties are +/-1 standard deviation. Revised thermodynamic properties of H4SiO4 based on this function are: ΔG°f(H4SiO4) = -1309.231 +/- 0.610 kJ/mol; ΔH°f(H4SiO4) = -1460.913 +/- 0.542 kJ/mol; S°(H4SiO4) = 180.87 +/- 0.49 J/mol K. The ΔG°f(H4SiO4) agrees well with the value of -1309.342 kJ/mol calculated from amorphous silica solubility of 116 ppm at 25°C. In addition, this new solubility function predicts low temperature quartz solubility values that are in good agreement with dissolved silica concentrations found in ancient groundwaters.