Calcite is not precipitated immediately from a supersaturated Ca-bicarbonate solution that becomes supersaturated by degassing CO/sub 2/. The degree of supersaturation increases until calcite begins to precipitate at ..delta..G approx. -1 kcal/mole. Over the whole range of the initial CO/sub 2/-degassing and the subsequent precipitation, the carbon isotope composition of the dissolved carbonate changes systematically. Measurements at the calcite-precipitating spring of Gueterstein, Germany indicate that this variation is controlled kinetically and cannot be attributed to a Rayleigh-type fractionation. An analytical expression for a kinetic model is derived. From this expression the ratio of rate constants for /sup 13/C- and /sup 12/C-species, controlling the partitioning, can be obtained.
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Michaelis et al. (1985) studied this question.