Partition coefficients in calcite: Examination of factors influencing the validity of experimental results and their application to natural systems

Abstract

Partition coefficients of metals in calcite have been of great interest in the study of the geochemistry of sedimentary carbonate mineral deposition and diagenesis. However, they are not equivalent to thermodynamic constants and generally represent phenomenological measurements under a given set of conditions. In recent years a number of factors, which were not previously considered of importance, have been found to exert major influences on the relation between the compositions of solutions and the calcites which precipitate from them. In this paper, we examine the complexities associated with the coprecipitation of metals in calcite using the behavior of Sr and Mg, which have received the most detailed study, as examples. Given the growing number of parameters which have been found to exert major influences on partition coefficients, and the failure of experimentally determined partition coefficients to predict even the composition of modern marine cements, we recommend that they be applied to natural systems with considerable caution.