Effect of the composition of zeolite paranatrolite on the configuration of its water-cation subsystem

The Rietveld method is used to determine the structure of two samples of high-hydrated zeolite paranatrolite: {Na_1.15Ca_0.38Sr_0.04(H₂O)_3.1}[Al_2.19Si_2.81O₁₀] (Vishnevye Mountains, Urals) and {Na_2.01K_0.04H_0.04(H₂O)_3.8}[Al_2.10Si_2.90O₁₀] (Kirov Mine, Khibiny Massif). Paranatrolite from the Vishnevye Mountains is characterized by the presence of split water positions and a relatively low total H₂O content. Local water-cation assemblages (WCAs) of three configurations are identified in the statistical “mixture”. The extraframework subsystem in the structure of Khibiny paranatrolite is made of WCAs of one configuration. The H₂O content of this mineral is close to the maximum possible amount and is a recordbreaker for natrolite-type minerals.