Figure 1. In situ Raman spectra of cristobalite at high pressures.

Spectra collected on two different single crystals of α-cristobalite at 1.1, 4.6, 8.6 and 15.0 GPa and at room temperature. Inset shows the DAC pressure chamber seen at 15.0 GPa: R stands for ruby; C1, C2 and C3 for different cristobalite crystals. In quasi-hydrostatic conditions (a) the crystal C1 starting as α-cristobalite (red) transforms via intermediate cristobalite-II (green) to cristobalite X-I (blue). However, in the case of high hydrostaticity (b), the smallest crystal C3 retains its initial structure of α-cristobalite (red). All spectra are unsmoothed, the background has been subtracted. Ar⁺ laser was used (514 nm excitation wavelength) with ∼0.8 W incident beam power.