Abstract
Abstract The effect of water on crystallization process of coesite was studied at 450 to 700 °C under 30 kbars by using different starting materials. The presence of water under compression and heating was found to have remarkable effects not only on the kinetics of crystallization of coesite also on the morphology of metastable quartz, consequently of coesite crystals. Under anhydrous condition, from amorphous silica and silica glass, the spherulitic aggregates of metastable quartz appeared. The coesite crystals were developed in the spherulites of quartz as elongated crystals with different sizes and appeared to be defective. When synthetic quartz was used as a starting material, however, no formation of spherulitic aggregates of quartz was observed and granular coesite crystals were obtained. Under hydrous condition, granular coesite crystals with homogeneous size were developed rapidly at 450 °C from both amorphous silica and silica glass through the discrete particles of metastable quartz.
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