Model of the Crystal Structure of Sodium-Depleted Sacrofanite. Problem of the Sacrofanite Identification

A structural model of the sodium-depleted analogue of sacrofanite, a 28-layer cancrinite-group mineral with the empirical formula (Na3.18Ca2.81K1.93)(Si6.10Al5.83Fe0.07O24)(SO4)1.95F0.51Cl0.19(OH)0.23⋅ 0.155H2O from sanidine syenite of the Sacrofano paleovolcano, Latium (Italy) has been built. The investigated mineral is hexagonal, sp. gr. P-62c, with the lattice parameters [a = 12.90519(13), c = 74.2181(10) Å, V = 10704.6(3) Å3] close to those of holotype sacrofanite. The aluminosilicate framework of the investigated sodium-depleted sacrofanite contains columns of zeolitic cavities of four types: cancrinite, sodalite, Losod, and liottite. Their presence is confirmed by the IR spectroscopy data, unlike holotype sacrofanite, the published IR spectrum of which contains no characteristic band of the liottite cage at 547 ± 4 cm–1.