A high compressibility is generally expected for open-framework structures due to the tetrahedral tilting, which produces inter-tetrahedral angle variations and accommodates the effect of pressure. In all cases, it is generally characterized by its volume. Several zeolites appear to be less compressible than many rock-forming minerals. There are two types of porosity: open porosity (on the external environment) and closed porosity. the tetrahedra), implies that the main deformation mechanisms at high-pressure (H P) are controlled by rigid (Si,Al)O 4-tetrahedral tilting 2) the structural rearrangement at H P is mainly driven by framework geometry and its topological symmetry 3) the compressibility of zeolites appears not to be directly related to the microporosity, represented by the “framework density” 4) the elastic parameters available for natural zeolites demonstrate that microporosity does not necessarily imply high compressibility. A semipermeable membrane, also termed a selectively permeable membrane, a partially permeable membrane or a differentially permeable membrane, is a membrane that will allow certain molecules or ions to pass through it by diffusion and occasionally specialized facilitated. The elastic data of zeolites reported so far allow us to infer that: 1) the peculiar characteristics of the zeolitic structure, with large channels and a flexible framework built of rigid units ( i.e. What does selectively permeable mean quizlet selectively permeable. This is a comparative study on lattice compressibility, pressure ( P)-induced structural deformation mechanisms and influence of the framework and extra-framework content on the elastic behaviour of zeolites, based on previously published data obtained by in situ H P-single crystal and powder diffraction experiments.