High-pressure structural behaviour of scolecite

The HP structural evolution of a natural scolecite from Iceland (space group Cc) was studied up to 5 GPa using in situ single-crystal X-ray diffraction data from a diamond-anvil cell (DAC) with silicon oil as non penetrating pressure transmitting medium. Linear regressions yielded mean axial compressibilities for a, b and c axes of βa = 4.4(2).10-3, βb = 6.1(2).10-3, βc = 6.0(1).10-3 GPa-1. K0, refined with a second-order Birch-Murnagham equation, fixing K0 at 4, is 54.6(7) GPa. The bulk scolecite structure compression was the result of the "soft" behaviour of the channels (K ≅ 17 GPa for [100]-channels; K ≅ 50 GPa for [001]-channels) and the more rigid behaviour of the tetrahedral framework (K ≅ 96 GPa), which underwent kinking of the Secondary Building Unit (SBU) along [100]-chains. The angle between the SBUs (φ), increased from 20.80(2)° at 0.0001 GPa, to 22.00(6)° at 3.38 GPa. Within the investigated pressure range, the position of the extra-framework cations and water molecules remained almost unchanged. Up to 4.2 GPa no phase transition was observed.