Stabilities of calcite and aragonite

Journal of Research of the U.S. Geological Survey
By: , and 



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.

Additional publication details

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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