title: A post-stishovite SiO2 polymorph in the meteorite Shergotty: implications for impact events.
abstract: Transmission electron microscopy and electron diffraction show that the martian meteorite Shergotty, a shocked achondrite, contains a dense orthorhombic SiO2 phase similar to post-stishovite SiO2 with the alpha-PbO2 structure. If an SiO2 mineral exists in Earth's lower mantle, it would probably occur in a post-stishovite SiO2 structure. The presence of such a high-density polymorph in a shocked sample indicates that post-stishovite SiO2 structures may be used as indicators of extreme shock pressures.
authors.affiliation: Department of Geology, Arizona State University, Tempe, AZ 85287, USA.
authors.forename: T G
authors.initials: TG
authors.lastname: Sharp
authors.forename: A
authors.initials: A
authors.lastname: El Goresy
authors.forename: B
authors.initials: B
authors.lastname: Wopenka
authors.forename: M
authors.initials: M
authors.lastname: Chen
mesh_terms: D003461:Crystallography; D018535:Mars; D019110:Meteoroids; D008854:Microscopy, Electron; D012822:Silicon Dioxide / Q000737:chemistry; D013059:Spectrum Analysis, Raman
chemical_list: D012822:Silicon Dioxide