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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 57 (1973)

Issue: 4. (April)

First Page: 787

Last Page: 787

Title: Interaction of Aqueous Mg2+ with Growing Calcite Crystals and its Effect on the Aragonite ^rarr Calcite Transformation Between 25 and 90 Degrees Celsius: ABSTRACT

Author(s): Amitai Katz

Article Type: Meeting abstract


The interaction of aqueous Mg2+ ions with growing calcite crystals was studied by closed system recrystallization of aragonite to calcite in the presence of aqueous CaCl2-MgCl2 solutions at 25-90°C. The measured heterogeneous coefficients for Mg2+ between calcite and solution (^lgr CMg2+) are independent of the solution's composition and rate of recrystallization. They are strongly dependent on temperature, being 0.0573 ± 0.0017 at 25°C, 0.0681 ± 0.0019 at 35°C, 0.0778 ± 0.0022 at 50°C, 0.0973 ± 0.0021 at 70°C, and 0.1163 ± 0.0034 at 90°C. If, as reported in literature, calcite containing 12-16 mole % magnesium has the same solubility as that of aragoni e, the new ^lgrCMg values exclude its formation directly from sea water. However, in closed systems isolated from seawater, the transformation of aragonite to calcite should start spontaneously once the magnesium-calcium ratio of the interstitial fluids drops from 5 to 2 or less, no freshwater intervention in this process being necessary.

The kinetics of recrystallization in the absence of Mg2+ at 25 and 35°C are strictly diffusion controlled and are, thus, markedly affected by the mass of aragonite per unit-volume of solution taking part in the process. The kinetic effect of Mg2+ is still under study.

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Copyright 1997 American Association of Petroleum Geologists