Elastic behavior and high-pressure (HP) structural evolution of a natural zeolite levyne, (Ca0.5,Na,K)6(Al6Si12O36)·18H2O, has been investigated up to 5 GPa by means of in situ single-crystal X-ray diffraction with a diamond-anvil cell using a non-penetrating pressure-transmitting medium. Peculiar elastic behavior has been observed in the range 0–1 GPa: the c parameter decreases between 0 and 0.2 GPa, then increases up to 0.5–0.6 GPa. Above this P-value, the parameter decreases as expected. Anomalous behavior is also shown by the a-parameter, which first increases up to 0.2 GPa, then decreases as expected. However, these anomalous lattice variations are only slightly reflected in the cell volume behavior. The low-P trend (P < 1 GPa) is also followed by the lattice parameters in decompression. The isothermal Equation-of-State (EoS) at P > 1 GPa, refined with a second-order Birch-Murnaghan EoS, yields the following parameters: V0 = 3539(3) Å3 and KT0 = 48(1) GPa. Comparison of structural refinements performed at 0.0001, 0.79(5), and 3.00(5) GPa highlights two distinct deformation mechanisms of the Si/Al-framework, one predominant at low pressures (0–1 GPa) and the other at high pressures (1–5 GPa).

The extra-framework content does not show any evident modification within the pressure range investigated.

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