Cleaved feldspar surfaces under dry and humid conditions: an AFM study

Abstract

The Earth’s surface is largely shaped by the interaction between water and the minerals of its crust. Feldspars, the most common aluminosilicates, are made of a framework of corner-sharing silica and alumina tetrahedra, enclosing cations such as potassium (K+ ), sodium (Na+ ), and calcium (Ca2+ ). The chemical re- actions at the feldspar-water interface contribute to geological processes such as erosion and weathering [1], clay formation [2], and ice nucleation [3], with im- plications for geology, agriculture, atmospheric chemistry, and climate science. We exposed cleaved surfaces of different feldspars to air and Ar with de- fined humidity and examined the evolution of their mesoscale morphology with atomic force microscopy (AFM). Overlayers with distinct patterns develop over time. They remain stable after rinsing the surface with ultrapure water, suggest- ing a permanent alteration of the surface morphology. We attribute the distinct patterns to local chemistry differences and different cation leaching rates [1]. [1] Brantley and White, Chem. Weath. Rates of Sil. Min. (2018) [2] Bleam., Clay Min. and Chem., 87-146 (2017) [3] Atkinson, et al., Nature 498, 355-358 (2013)