Some Preliminary Thermodynamic and Kinetic Considerations

At this junction it seems appropriate to consider some further thermodynamic and kinetic arguments that bear on carbonate diagenetic problems discussed in this chapter and in Chapters 7 and 8. Because most carbonate diagenetic reactions take place in an aqueous environment (seawater, freshwater, brines) over a range of temperature and pressure, it is rapidly becoming 

It should be emphasized that an equilibrium can be established between a metastable phase(s) and its environment. Aragonite, for example, can be precipitated from seawater at 25°C, but it is unstable at Earth-surface T and P, and can persist metastably because of kinetic reasons. This statement is illustrated by the following calculation. We can use the free energies of formation of Table 6.1, and calculate the Gibbs free energy of reaction for the mass action equation representing aragonite-calcite equilibrium  

surface seawater is IAP/Ksat = 4.3 times oversaturated with respect to this phase, but the magnesian calcite should spontaneously convert to nearly pure calcite plus dolomite according to  

It is the case that in surface seawater at 25°C, the ion activity products of all the minerals aragonite, magnesian calcite (15 mole %), calcite and dolomite are 

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