The high-pressure behavior of balliranoite: a cancrinite-group mineral

The high-pressure elastic behavior and structure evolution of a natural balliranoite, i.e. a mineral isotypic with cancrinite belonging to the davyne subgroup, (Na-4.47 Ca2.86K0.11)(Si5.96Al6.04O24)Cl-2.03(CO3)(0.78)(SO4)(0.33), a = 12.680(1) angstrom, c = 5.3141(5) angstrom and V = 739.9(1) angstrom(3), S.G. P6(3), have been studied by means of in-situ single-crystal X-ray diffraction with a diamond anvil cell, up to 6.77(2) GPa. No evidence of phase transition, structure collapse or change of the compressional behavior have been observed within the pressure range investigated. The unit-cell volume evolution as function of pressure has been fitted with a second-order Birch-Murnaghan equation of state (BM EoS), yielding the following refined parameters: V-0 = 735.5(7) angstrom(3), K-v0 = 48.1(8) GPa. Fitting of the a vs. P and c vs. P data with linearized third-order BM-EoS leads to the following elastic anisotropy at ambient conditions: K-a0 : K-c0 = 1.35 :1. The P-induced structure evolution of balliranoite is mainly governed by the framework re-arrangement through tilting of quasi-rigid tetrahedra. A comparative analysis of the elastic behavior and of the structure deformation mechanisms of balliranoite and cancrinite at high-pressure are carried out.