Untersuchungen über das Gleichgewicht zwischen K-Feldspat, Quarz und Muskovit und die Anwendung auf Fragen der Gesteinsbildung bei tieferen Temperaturen
✍ Scribed by H. E. Usdowski; H. L. Barnes
- Publisher
- Springer
- Year
- 1972
- Tongue
- English
- Weight
- 753 KB
- Volume
- 36
- Category
- Article
- ISSN
- 0010-7999
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✦ Synopsis
During equilibration of K-feldspar, quartz and muscovite with dilute KCl-solutions, the change in pH of the solution was measured as a function of time. The resulting equilibrium constant, K T = a K +/att +, is 104-~14-0.08, 105.s6 • and 106.~ at 300, 60 and 30 ~ C respectively (standard states at 1 bar) and are consistent with the best higher temperature data. At 30~ this constant is consistent with the a K +/at~ + ratio of seawater. From K T and the activity of K + in seawater, a pH of 8.2 is calculated, essentially identical with the pH which results from dissolution of CaCO 3 under atmospheric C02-pressurc. Consequently, detrital K-feldspar, quartz, muscovite, and calcite are stable in seawater. Apparently, the seawater-pH is controlled by CaCO 3 as well as K-feldspar, quartz and muscovite. Independently both equilibria show virtually f2~e same pit, within the variability due to disordering, solid solution and surface energy effects.
Assuming that the K-concentrations of pore solutions vary between about 4000 and 40 ppm, these solutions have alkalic pH-values in the temperature range between 30 and 300 ~ C if K-feldspar, quartz and muscovite are present. In limestones the pH is fixed by the dissociation of CaCOa; the occasionally observed formation of K-feldspar in these rocks requires a minimum K-concentration of approximately 4 ppm.