Structural and morphological evolution of biogenic silica under high pressure and high temperature conditions

Abstract

The structure of diatom frustule was transformed to opal-CT just after compression under 100 ^oC without the morphological change, and then its structure and morphology were retained at least up to 6.9 GPa. With keeping the compression of 5.7 GPa under 100 ^oC for 7 days, the structure was changed to coesite. After 7 days under 0.3 GPa and 100 ^oC, the structure of diatom frustule was changed to a mixture of a-moganite and a-quartz, which was an approximately similar texture to chalcedony.