Cultures of known species of fungi placed on crystals of Iceland spar calcite resulted in extensive dissolution of the calcite. This organically mediated dissolution produced large patches of spiky calcite within a period of 253 days. The dissolution of the calcite occurred via surface-reaction-controlled kinetic processes that were mediated by the fungi. This occurred despite the lack of vast quantities of fluids undersaturated with respect to calcite. Locally, at least 10 mu m of calcite was removed from the original crystal surface.