Effects of local mechanical collision with shear stress on the phase transformation from α -quartz to coesite induced by high static pressure

A laboratory method combining high-energy mechanical ball milling and high static pressure has been suggested for modeling synthesis of coesite in the Earth's crust. The window of milling time, the mechanical-collision-induced intermediate phase of α -quartz, and its conditions for easily crystallizing into coesite induced by high static pressure 3.0 GPa (923 K, <1.0 min) have been discovered. These are a much shorter synthesizing time and lower synthesizing critical pressure than obtained before. The Raman spectrum for the coesite synthesized by the present method has a larger number of peaks and includes the information of the natural and synthesized coesites reported before. Here we clarify the implications of the coesite synthesized by this method in geoscience, and suggest another possible formation mechanism of coesite in the Earth's crust, which is different from the hypothesis of plate subduction-exhumation in the Earth that was based on coesite formation conditions under high static pressure in the laboratory.