Pressure dependence of color of natural uvarovite:: the barochromic effect

The electronic absorption spectra of natural uvarovite containing 62 mole% of the Cr3+ end-member were studied at pressures between 10(-4) and ca. 13 GPa using DAC techniques combined with microscope spectrometric device. With increasing pressure, a barochromic effect with change from green to red color of the garnet specimen was observed. This change could be interpreted on the basis of the spectra and the data points derived in an ICE color card. The evaluation of crystal field data from the spectra showed that 10Dq of chromium increases on pressure while the Racah parameter B, and thus the nature of the chemical bond of Cr-O does not change significantly.