Amorphization of natrolite and edingtonite at high pressure

Amorphization of natrolite Na₂[Al₂Si₃O₁₀]2H₂O (Khibiny, Kola Peninsula, Russia) and edingtonite Ba[Al₂Si₃O₁₀]4H₂O (Böhlet, Sweden) was investigated at high pressures up to 11 GPa, using Raman spectroscopy. Natrolite compressed in a non-penetrating medium of methanol-ethanol shows one apparent crystal-to-crystal transition at approximately 3.7 GPa before amorphization. Amorphization, reflected by decrease of Raman spectrum intensity, starts in the pressure range of 6–7 GPa and is completed by ~9 GPa. Amorphized Na₂[Al₂Si₃O₁₀]2H₂O exhibits partial reversibility to crystalline natrolite after amorphization at ~7-8 GPa and partially recovers its Raman spectrum after release of pressure. It was shown that amorphization of natrolite begins in soft structural units (water sublattice) and finishes in rigid units (T-O bonds).

Comparison of natrolite and edingtonite behaviour at high pressures shows that amorphization of both zeolites begins at similar pressures but differ in their crystalline phase transitions. Edingtonite compressed in methanol-ethanol has no crystalline transition at high pressure. Ba[Al₂Si₃O₁₀]4H₂O amorphized after compression up to higher pressure of ~11 GPa also exhibits partial reversibility to edingtonite crystal structure on release of pressure.