Our shock metamorphism experiments suggest Coesite forms in Opal-A at low pressures in contrast to previous believes

Our study published in ACS Earth and Space Chemistry suggests that Coesite forms in Opal-A at low pressures than what was previously thought. Opal-A is a hydrated amorphous silica species and a widespread mineraloid on Earth’s crust that occurs in vesicles, veins, and fissures of many rocks (e.g., commonly found with sandstone, chalk deposits, limonite, and rhyolite). On Mars, the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument suggests the presence of opaline silica deposits on the Martian surface. In this study, we report the first impact experiments on opal-A. The phase transformation and deformation features of shocked opal-A were investigated by synchrotron XRD and TEM analyses. The results of this study provide important information on the shock metamorphism of opal-A from macro to nanoscales.

Cai and Thevamaran collaborated with UW Geoscientists Lee, Xu, and others in this study.

Read the full article at: https://pubs.acs.org/doi/10.1021/acsearthspacechem.0c00090