Two basic pore macrostructures can mainly be distinguished (CEDEX, 2007; Serrano et al, 2007a & b; Santana et al, 2008):a. reticular structure (Fig. 1a) b. vacuolar structure (Fig. 1b)The reticular type corresponds to the pore structure of the rock made up of an aggregate of particles joined together either by the heat action produced in their formation, or by some type of cement. The vacuolar type corresponds to the pores of a rock which are all vacuolar in type, formed due to the gas formed inside the viscous lava as it is expelled from the volcano.