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, (Na4:47Ca2:86K0:11)(Si5:96Al6:04O24)Cl2:03(CO3)0:78(SO4)0:33, a = 12.680(1) Å, c = 5.3141(5) Å and V = 739.9(1) Å3, S.G. P63, 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 unitcell 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: V0 = 735.5(7) Å3, KV0 = 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: Ka0 : Kc0 = 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.