Geochemistry

Reversing Crystal Growth

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Science  11 Nov 2005:
Vol. 310, Issue 5750, pp. 945-947
DOI: 10.1126/science.310.5750.945d

Much of the chemistry and dynamics of Earth's surface depends on the dissolution of minerals: It determines the composition of soils, rivers, and oceans and affects the amounts of major gases, such as CO2, in the atmosphere. Rapid dissolution weakens rocks, facilitating erosion, and dissolution and corrosion are critical in evaluating the performance of engineered structures. Various data have implied that the dissolution rates of many minerals are complex functions, depending subtly on interacting waters, for example.

Dove et al. show, both theoretically and through experiments, that for quartz, and likely for other silicate minerals, well-developed theories of crystal nucleation and growth can be used to understand dissolution. Nucleation theory involves four parameters: temperature, oversaturation, and two parameters that describe the energy and kinetics associated with a step on a growing crystal. The authors derive the analogous equations for dissolution at dislocations and vacancies, and show that the theory fits well with experimental data for quartz, feldspar, and a common clay mineral, dissolving in waters under a range of pH and salt conditions. If the result holds across a full range of minerals, it would allow the prediction of dissolution and corrosion under a variety of conditions and temperatures. — BH

Proc. Natl. Acad. Sci. U.S.A. 102, 15357 (2005).

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