Assessment of feldspar solubility constants in water in the range of 0 to 350 C at vapor saturation pressures

Journal Article · Mon Mar 01 04:00:00 EST 1999 · American Journal of Science

DOI:https://doi.org/10.2475/ajs.299.3.173· OSTI ID:355675

Arnorsson, S; Stefansson, A ^[1]

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1. Univ. of Iceland, Reykjavik (Iceland). Science Inst.

The equilibrium constants for endmember feldspar hydrolysis for the following reactions: NaAlSi{sub 3}O{sub 8} + 8H{sub 2}O = Na{sup +} + Al(OH){sub 4}{sup {minus}} + 3H{sub 4}SiO{sub 4}{sup 0}; KAlSi{sub 3}O{sub 8} + 8H{sub 2}O = K{sup +} + Al(OH){sub 4}{sup {minus}} + 3H{sub 4}SiO{sub 4}{sup 0}; CaAl{sub 2}Si{sub 2}O{sub 8} + 8H{sub 2}O = Ca{sup +2} + 2Al(OH){sub 4}{sup {minus}} + 2H{sub 4}SiO{sub 4}{sup 0} are accurately described by five equations where temperature is in K. They are valid in the range 0 to 350 C, at 1 bar below 100 C and at vapor saturation pressures (P{sub sat}) at higher temperatures. The equations for low-albite and microcline are valid for Amelia albite and for microcline with the same degree of Al-Si order (Z = 0.95), respectively. The same kind of log K-temperature equations have also been retrieved for alkali-feldspar and plagioclase solid solutions. The calculated feldspar equilibrium constants of this study indicate much higher solubility under weathering conditions than generally accepted to date, the difference being more than one and a half orders of magnitude at 0 C for both high- and low-albite, but somewhat less for microcline, sanidine, and anorthite. This higher solubility is largely a consequence of new data for the thermodynamic properties of H{sub 4}SiO{sub 4}{sup 0}. The present results have a particularly important bearing on the stability of feldspars under weathering conditions and the study of interaction between water and rock/soil in this environment. They are, however, also important for the study of equilibrium/dis-equilibrium conditions in active geothermal systems.

• Sponsoring Organization: USDOE
• OSTI ID: 355675
• Journal Information: American Journal of Science, Journal Name: American Journal of Science Journal Issue: 3 Vol. 299; ISSN AJSCAP; ISSN 0002-9599
• Country of Publication: United States
• Language: English

Related Subjects

15 GEOTHERMAL ENERGY
FELDSPARS
GAS SATURATION
HYDROLYSIS
KINETIC EQUATIONS
ROCK-FLUID INTERACTIONS
SOLUBILITY
WATER VAPOR
WEATHERING