Hydrogen figures importantly in many geologic processes. Yet the structural role of hydrogen in minerals is not well understood, mainly because of the difficulty in accurately locating a hydrogen atom in a structure. Hypothetical hydrogen positions from energy calculations can provide useful insight into certain problems related to the role of hydrogen. Practical applications are concerned with improving the interpretation of structure determinations based on diffraction experiments and improving the interpretation of spectroscopic observations (infrared absorption Raman emission). This article reviews ionic theory, as it pertains to hydrogen in minerals, and describes applications of energy calculations to problems in muscovitc, the humite group, topaz and amphiboles.