Porosity generated during the fluid-mediated replacement of calcite by fluorite

Abstract

Mineral replacement reactions are common phenomena in natural and laboratory environments where solids have re-equilibrated with aqueous solutions and are characterized by the generation or destruction of porosity in the product phase(s). Here, the evolution of porosity during the replacement of calcite by fluorite is used as a model system to characterize the kinetics of volume variations. Non-porous single crystals of calcite were reacted with sodium fluoride solutions for different reaction times. The crystals were pseudomorphically replaced by highly porous fluorite. Complementary use of porosimetry techniques, high resolution imaging, and mass-balance calculations revealed the total, open, and closed porosity in the samples. The infiltration of aqueous fluids in the Earth depends on the evolution of porosity and hence porosity variations are important in various geological processes such as, rock weathering and soil formation, fluid-controlled metamorphism, mineral ore emplacement, or oil and gas reservoir compaction. Such mechanisms can also be used to develop geo-inspired materials designed for industrial and medical applications.