Stabilities of calcite and aragonite
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Abstract
A revaluation of the 25° C activity-product constants of calcite (KC) and aragonite (KA) was made on the basis of the known solubilities of these phases for which the activity of total dissolved calcium was corrected for the presence of the ion pair CaHCO3+ in the aqueous phase. The value of the dissociation constant of CaHCO3+ was taken to be 10-1.225±0.02. This value, combined with values of the analytical concentrations in solutions with partial pressure PCO2 =0.97 atmosphere, leads to KC=l0-8.52±0.04 and KA= 10-8.36±0.04. Based on these K values, standard free energies of formation of calcite and aragonite were calculated to be -270,144±375 and -269,926±375 calories mole-1, (-1,130,282±1,569 and -1,129,370±1,569 joules mole-1), respectively. From the 25°C K values, using appropriate entropy and heat capacity data, values of KC and KA were calculated over the temperature range 0° to 200°C. Possible errors in interpretation of measured pH values and inferred PCO2values and the bearing of these errors on calculations of K values are discussed.
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Stabilities of calcite and aragonite |
| Series title | Journal of Research of the U.S. Geological Survey |
| Volume | 2 |
| Issue | 2 |
| Year Published | 1974 |
| Language | English |
| Publisher | U.S. Geological Survey |
| Publisher location | Reston, VA |
| Description | 10 p. |
| First page | 175 |
| Last page | 184 |
| Online Only (Y/N) | N |
| Additional Online Files (Y/N) | N |
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