2. Petrographic description of rocks

The physical and mechanical properties of a rock are linked to its mineralogical composition and petrofabrication, which is the result of its formation and the geological history it has undergone. A preferred orientation of minerals, linked for example to the acquisition of schistosity or foliation, will generally result in anisotropic physical, mechanical and hydraulic properties. Similarly, the presence of voids, such as porosity or microcracking, will influence these same properties. The first step is therefore to carry out a petrographic description of the rock matrix. This petrographic description consists in determining the nature of the various minerals, their proportion, degree of alteration, size and arrangement (texture), as well as the possible existence of pores and microcracks. Various techniques can be considered for this petrographic description (in decreasing order of resolution):...