High Pressure Raman Study of Laumontite Overhydration in Different Water-Containing Media

Abstract
Laumontite overhydration was studied using Raman spectroscopy. Compression in water (up to 9.3 GPa) and in water-alcohol medium (MEW – methanol / ethanol / water 16 / 3 / 1, up to 5.8 GPa) were compared. Sample Ca-Na-K-laumontite fr om Akhaltsikhe, Georgia was selected. The mineral formula is {Ca_2,73Na_1,44K_1,03(H₂O)n} [Al_7,93Si_16,07O₄₈], wh ere 12< n <18 depending on the humidity and pressure of the medium. By means of Raman spectroscopy, a heterogeneous state of Ca-Na-K-laumontite at P = 0–2.2 GPa in MEW medium was revealed, in contrast to compression in water. An increasing difference between wavenumber/pressure dependencies (2.2–4.5 GPa) related to compression in water and MEW can be ascribed to penetration of additional amount of water in crystal channels during compression in ice VII. A polymorphic transition in laumontite at 4.5–4.8 GPa was also detected. The onset of the disordering laumontite structure was observed at pressure above 8 GPa.

Keywords
Raman spectroscopy, laumontite, zeolites, high pressure
Acknowledgements
This work was supported by the state assignment (project no. 0330-2016-0004) and the Russian Foundation for Basic Research (grant no. 18-05-00966_a) 
УДК 538.95; 539.3

High Pressure Raman Study of Laumontite Overhydration in Different Water-Containing Media