The principles of scanning probe microscopy (SPM) are illustrated with examples from oilfield mineralogy, particularly emphasising sulphate minerals involved in scale formation and cement hydration chemistry. The topography of the (010) cleavage surface of gypsum observed by atomic force microscopy shows atomically flat terraces separated by shallow steps often only one unit cell high. SPM allows direct observation of processes on mineral surfaces while they are in contact with solutions. The dissolution etching and crystal growth of gypsum and barite are discussed and rates of step migration estimated. The orientation of steps is related to the crystallographic axes. The action of phosphonate crystal growth inhibitor on gypsum and of a chelating scale solvent on barite are also shown. The multiphase microstructure of an oilwell cement clinker is described in relation to its hydration chemistry in contact with water and its reaction with sulphate ions.

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