Karst, by definition, is the result of rock dissolution. If the rock is not completely soluble, residues will remain ("acquired" particles). This insoluble material, present in the springs issuing from the karst body after some time lag, provides information regarding karst processes taking place within the rock body. The presence of pathways between the surface and the endokarst is reflected by an increase in the suspended particulate material (SPM) that may be considered to be "inherited" from outside of the karst system. By the study of microgranulometric spectra the origins of the particles are differentiated and, on this basis, a classification of karst systems is proposed. The technique was applied to the chalk karst of Haute Normandie (France) by obtaining characterisations of the microgranulometric fraction of the main surface formations (clay-with-flints and loess) and that produced by dissolution of the chalk. By the comparison of these spectra with those of the SPM contained in ten karst springs, it was possible to define two types of karsts ("open" and "closed") and their intermediates. In "closed" karst a majority of the particles originated from the dissolution of the chalk itself, while in the "open" karst, the majority of the particles are derived from the surface formations. This notion of "aperture" is quite different from the conventional allogenic/authigenic karst classification which implies the formation of an impermeable residual soil that focuses surface water inputs.