The kinetics of the reaction, Biogenic carbonate + Mg⁺⁺ ^rarr Dolomite + Ca⁺⁺, have been studied at 300°C. in aqueous solution. Within the dolomite stability field the rate of dolomitization is increased by the following.

a. Increased instability of the reactant.
b. Increased calcium plus magnesium concentration of the dolomitizing solution.
c. Increased magnesium/calcium ratio of the dolomitizing solution.
d. Increased molar solution/solid ratio.
e. Increased temperature.

Each of the above five kinetic variables favors dolomitization in hypersaline environments. However, dolomitization has not yet been precluded in a normal marine environment.

Present carbonate-forming sediments consist predominantly of the metastable minerals aragonite and magnesium calcite. At 300°C. these minerals, compared with calcite, are preferentially dolomitized. In nature, at lower temperatures, similar preferential reaction is observed. In limestone from Bonaire and Jamaica, the magnesium calcite components, in most cases red algae, have been replaced selectively by dolomite. Such preferential dolomitization indicates the penecontemporaneity of the process. The dolomitizing reaction is the mechanism whereby the

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metastable mineral equilibrated.

Because aragonite and magnesium calcites, in most cases, equilibrate moderately rapidly in time, either by replacement, inversion, exsolution, or dissolution, their disappearance from a rock might be a logical process of carbonate diagenesis. If true, diagenetic processes, as opposed to post-diagenetic processes, would in many cases reflect the environment of deposition.

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