Pressure Induced Polymorphic Phase Transition of Natural Metamorphic Kalsilite; Electrical Resistivity and Infrared Spectroscopic Investigations

We report here pressure dependence of the electrical resistivity of natural kalsilite (K0.998Na0.002Al0.998Fe0.002SiO4) from a granulite facies terrain in southern India. The electrical resistivity of kalsilite was measured with four probe technique up to 7.5 GPa at room temperature. The electrical resistivity decreases continuously with the increase of pressure up to 3.7 GPa, where there is a discontinuous drop in the electrical resistivity by 14%–16% indicating a first order transition. Further increase of pressure does not induce any phase transition up to 7.5 GPa at room temperature. Fourier transform infrared (FTIR) spectroscopy of the kalsilite sample at various pressures indicates that the observed transition is reversible in nature.