An X-ray single crystal study of alkaline cations influence on laumontite hydration ability: II. Pressure-induced hydration of Na,K-rich laumontite

In the present work the influence of alkaline cations on pressure behavior of laumontite |(Ca4−xNax)Kx(H2O)n|[Al8Si16O48] was studied using single-crystal X-ray diffraction in diamond-anvil cell with water medium. Na,K-rich laumontite, containing 13.4 H2O molecules per formula at ambient pressure (0.0001 GPa), hydrates up to ≈15.5 H2O in the pressure range of 0.0001–0.75 GPa. This pressure-induced hydration occurs due to the occupancy increase of already populated water sites and does not cause any essential structure changes. The bulk modulus K0 = 39(3) GPa was evaluated for Na,K-rich laumontite using normalized volumes.

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► Na,K-rich laumontite demonstrates pressure-induced hydration.
► The pressure-induced hydration occurs in two steps.
► The first step of pressure-induced hydration causes an abrupt volume expansion.
► The second step of pressure-induced hydration (0.2–0.75 GPa) is regular.
► The pressure-induced hydration does not affect H-bonds arrangement.