Relationships between mineralogy and porous medium of the craie tuffeau (Paris Basin, France)

55 tuffeau blocks coming from historical monuments being restored, and quarries that supply building blocks for restoration work were subjected to a physical and chemical characterization. Petrographically, tuffeau consists of a continuous series that is based on the ratio between visible detrital minerals, in particular quartz and glauconite, and siliceous micrite. The Tuffeau de Saumur and the Tuffeau de Bourré are the end-members of this series. Tuffeau is an extremely porous rock, with an average total porosity of 44 % and an extended porosity spectrum. This is shown by a macroporosity and microporosity that, respectively, are 22 and 17 % (mercury porosimetry), and an average value of 9 % for infraporosity obtained from nitrogen adsorption-desorption isotherms : _ macroporosity is dominated by inter-spherules of CT opal macropores. The remaining part of the macroporous domain is originated by large-sized mineral crystals (quartz, glauconite. muscovite. sparitic calcite) along with organism test fragments ; _ microporosity is related to the compactness and arrangement style of micrite crystals. The nature of the surface of CT opal spherules, shaped like overlapping ridges, also creates a significant proportion of this microporous domain; _ infraporosity corresponds to intraleaf and intertactoïd pores of clay minerals as well as to the microroughness of some other minerals such as. in particular, micrite calcite.