Eight samples of prehnite from southern Africa were analysed for their major and trace element geochemistry to investigate the controls on their compositions. Variations in the major elements are limited (Fe3+-Al exchange, limited enrichment in Mn), and trace elements typically occur at levels <10 ppm, apart from Ga and sometimes Ti. The main control on the low trace element contents appears to be the small size of the crystallographic sites. Nevertheless, variations were observed in several elements, such as B, Ti, Sc, W, Mo, As and the rare earth elements. These variations imply a control by the host rock and its surrounds, as well as the identity of co-existing minerals.