| Summary: | Throughout Earth, rocks respond to changing physical and chemical conditions by converting one rock type to another. These conversions have conventionally been described in terms of solid-state mechanisms, in which new minerals nucleate and grow through exchange of elements by diffusion. The slow rates of solid-state diffusion suggested geological time scales for these processes. However, rocks in Earth's crust are not dry (1), and even very low concentrations of aqueous solutions can increase reaction rates substantially (2). In the presence of a fluid phase, mineral conversions turn out to proceed not via solid-state diffusion but through dissolution and recrystallization at the mineral-fluid interface (3). Well beyond mineralogy, these insights may prove useful in developing new methods of materials synthesis, for carbon removal from the atmosphere, and for safe nuclear waste storage.
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