Abstract
Solution composition-sensitive disjoining pressure acting between the mineral surfaces in fluid-filled granular rocks and materials controls their cohesion, facilitates the transport of dissolved species, and may sustain volume-expanding reactions leading to fracturing or pore sealing. Although calcite is one of the most abundant minerals in the Earth’s crust, there is still no complete understanding of how the most common inorganic ions affect the disjoining pressure (and thus the attractive or repulsive forces) operating between calcite surfaces. In this atomic force microscopy study, we measured adhesion acting between two cleaved (104) calcite surfaces in solutions containing low and high concentrations of Ca2+ ions. We detected only low adhesion between calcite surfaces, which was weakly modulated by the varying Ca2+ concentration. Our results show that the more hydrated calcium ions decrease the adhesion between calcite surfaces with respect to monovalent Na+ at a given ionic strength, and thus Ca2+ can sustain relatively thick water films between contacting calcite grains even at high overburden pressures. These findings suggest a possible loss of cohesion and continued progress of reaction-induced fracturing for weakly charged minerals in the presence of strongly hydrated ionic species.
Highlights
Calcite is one of the most ubiquitous nonsilicate, rock-forming minerals found abundantly in many distinct geological environments
Our symmetric system with two calcite surfaces is experimentally challenging due to undefined contact topography, our work provides strong insight into ion-dependent adhesion
We showed that the adhesive forces acting between the weakly charged calcite surfaces in Ca2+bearing aqueous solutions are not strongly affected by varying Ca2+ concentrations
Summary
Calcite is one of the most ubiquitous nonsilicate, rock-forming minerals found abundantly in many distinct geological environments. The interfacial properties and cohesion of (104) calcite surfaces in contact with geologically relevant solutions are suggested to influence several major deformation processes, including chemomechanical weathering,[1] fluidinduced subsidence and water-weakening,[2−4] subcritical fracturing,[5] and carbonate-hosted seismicity.[6] Solution composition-dependent disjoining pressures (DPs), associated with water films sustained on mineral grains in calcite-bearing rocks and in a wider range of mineralogical settings, may control reaction-driven fracturing processes[7,8] and damage by salt crystallization.[9] More information is needed on the ionspecificity of surface forces and cohesion in all of these systems to understand the nanoscale details of these common deformation processes
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