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A post-stishovite SiO2 polymorph in the meteorite Shergotty: implications for impact events
T G Sharp1, A El Goresy, B Wopenka
1Department of Geology, Arizona State University, Tempe, AZ 85287, USA.
Science (New York, N.Y.)
|May 29, 1999
Summary
Martian meteorite Shergotty contains a dense SiO2 phase, similar to Earth's lower mantle post-stishovite structure. This high-density polymorph can serve as an indicator of extreme shock pressures on planetary bodies.
Area of Science:
- Geochemistry
- Mineralogy
- Planetary Science
Background:
- Martian meteorites provide insights into planetary formation and evolution.
- Understanding high-pressure phases of silica (SiO2) is crucial for deep Earth and planetary interior models.
Purpose of the Study:
- To investigate the mineralogical composition of the martian meteorite Shergotty.
- To identify high-pressure silica polymorphs within extraterrestrial samples.
- To assess the potential of these polymorphs as indicators of shock events.
Main Methods:
- Transmission electron microscopy (TEM) was employed to analyze the microstructure of the Shergotty meteorite.
- Electron diffraction was used to determine the crystallographic structure of the identified phases.
Main Results:
- A dense orthorhombic SiO2 phase, structurally analogous to post-stishovite with an alpha-PbO2 structure, was identified in Shergotty.
- This phase represents a high-density polymorph of silica.
- The presence of this polymorph in a shocked achondrite suggests extreme shock pressures were experienced.
Conclusions:
- The martian meteorite Shergotty contains a high-pressure silica polymorph similar to that expected in Earth's lower mantle.
- Post-stishovite SiO2 structures can be utilized as reliable indicators of extreme shock pressures in shocked meteorites and potentially in planetary interiors.
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