Geomycology can be simply defined as ‘the scientific study of the roles of fungi in processes of fundamental importance to geology’. As such it can be considered as a sub-discipline of geomicrobiology and a component of biogeochemistry. The geomycological importance of fungi is significant in several key areas, such as nutrient and element cycling, rock and mineral transformations, bioweathering and mycogenic biomineral formation. Such processes can occur in aquatic and terrestrial habitats, but it is in the terrestrial environment where fungi probably have the greatest geochemical influence. Of special significance are the mutualistic relationships with phototrophic organisms, lichens (algae, cyanobacteria) and mycorrhizas (plants). Centra...