The very low permeability of argillites
Argillite seen with an electron microscope. In the matrix you can see macropores (P), grains of quartz (Q) and calcite (Cal). The argillite particles leave 10 to 18% minuscule pores, spaces that can hold very small quantities of water, between them. The circulation of this water is extremely limited. Because the quartz, a highly resistant mineral, is a good conductor of heat, the rock is solid and is capable of removing the heat released by the radioactive waste. The chemical environment is stable due to the presence of 25% carbonates, which regulate the acidity of the rock.