Ion partitioning and element mobilization during mineral replacement reactions in natural and experimental systems

Mineral replacement is a common phenomenon in a wide range of geological environments. Metasomatism, metamorphism, weathering, diagenesis and fossilization are examples of processes that can involve the replacement of one or more minerals associated with extensive chemical change. Such replacements are very often pseudomorphic. At relatively low temperatures such as those at the surface or within the upper part of the Earth's crust, where solid-state diffusion can be considered negligible, mineral replacement is the result of interface-coupled dissolution-precipitation reactions, driven by the interplay between the degrees of saturation of natural fluids with respect to different mineral phases. These reactions can play an important role in the mobilization and partitioning of elements. Mineral replacement is accompanied by the generation of porosity, which provides a pathway for the penetration of the fluid within the original parent mineral and facilitates mass transport. This chapter highlights the importance of dissolution-precipitation mineral replacements for element mobilization and ion partitioning in the Earth by presenting and discussing both experimental models and examples of natural processes, development of which can involve significant chemical change, such as during serpentinization and bone fossilization. © 2010 the European Mineralogical Union and the Mineralogical Society of Great Britain &Ireland