Coesite-Stishovite transition

The coesite-stishovite transition curve has been determined over the temperature range 550° to 1200°C in the pressure range 82.0 to 98.0 kb by means of a tetrahedral-anvil type of high-pressure apparatus. Amorphous anhydrous silica, α quartz, coesite, and stishovite were used as starting materials. The transition curve was fitted by the linear equation P (kb) = 69 + 0.024 T (°C) by using the pressure scale proposed by Jeffery et al. This determination was found to be in reasonable agreement with the previous data, if the common pressure scale is used. Experimental information for the coesite-stishovite transition was also compared with the stability relation derived from enthalpies and entropies of coesite and stishovite. It was suggested that the pressure scale proposed by Jeffery et al. was considerably underestimated around 100 kb.