Raman spectra of shortite Na₂Ca₂(CO₃)₃ compressed up to 8 GPa

<p>A rare mineral shortite, Na₂Ca₂(CO₃)₃, occurs among groundmass minerals in unaltered kimberlites, which suggests its participation in the evolution of kimberlite system. This work presents a high pressure Raman spectroscopic study of natural shortite (Udachnaya east kimberlites) compressed in KBr up to 8 GPa in a diamond anvil cell. At ambient pressure the spectrum contains two strong bands related to symmetric C-O stretching vibrations, four in-plane bending modes, and several low-frequency modes of lattice vibrations. Upon the pressure increase up to 8 GPa, almost all the bands exhibit positive shift with the rate of 1–4 cm⁻¹/GPa for the lattice modes and 3.6 and 3.9 cm⁻¹/GPa for the C-O stretching modes. The shifts of Raman modes are rather regular, which implies the absence of reconstructive phase transitions within the studied pressure range, similarly to the behavior of nyerereite, a related carbonate mineral. However, minor anomalies in the ν/<i>P</i> and FWHM/<i>P</i> dependences, observed at about 2 GPa, suggest some rearrangement and disordering of carbonate groups. The obtained data can be used for the estimation of residual pressure in shortite-bearing inclusions in deep-seated minerals.