Mineral surfaces – Part I: Surface-sensitive techniques
Over the decades that Earth scientists have been studying the solids and fluids of the Earth, our traditional mineralogical and geochemical methods have taught us a great deal about the composition and properties of the materials that make up our surroundings in nature and also about the materials of the deep Earth and the Universe. Through this information, we have been able to form conceptual models about the reactions that take place at mineral surfaces, at the interface between solid and fluid – be it a gas, a solution, or a melt. An interface is a boundary between phases. It is at the interface, the growing or dissolving front of the solid, where composition of both solid and fluid are defined and mineral structure and morphology are determined. Even processes such as solid-state diffusion and mineral transformation under heat and pressure, begin at a point or a line that may be a physical defect or a chemical inhomogeneity, and continue along a front that separates properties that are slightly different than in the rest of the solid.
Earth scientists have many bulk analytical methods at their disposal. Typically, we have been able to choose among: X-ray diffraction (XRD), electron microprobe (EPMA), scanning electron microscopy (SEM), inductively coupled plasma mass or atomic emission spectroscopy (ICP-MS or ICP-AES), atomic absorption spectroscopy (AAS), optical and other forms of microscopy, infrared, Mössbauer and other forms of spectroscopy, potentiometry, chromatography and other wet-chemistry methods. These techniques give us information about the morphology, composition and structure of minerals