A widely distributed bluish fluorescence, excited by 365 mμ. is frequently enhanced by weak annealing and always destroyed by heating to red heat. It is found in atmospheric dust and condensation products, in surface waters, in sedimentary and in magmatic minerals as well as in some meteorites. It is due to traces of organic substances and not identical with the Ewles-effect (fluorescence of adsorbed water). A systematic investigation might lead to geologically significant results.