Characterization of a high-pressure phase of silica from the Martian meteorite Shergotty

Abstract

Recently, there has been substantial interest in post-stishovite high-pressure polymorphs of SiO₂, discovered as extraterrestrial minerals, or synthesized in the laboratory. Previous investigators reported the presence of “α-PbO₂-like” and “baddeleyite-like” SiO₂ in the Martian meteorite Shergotty, and also the synthesis of an α-PbO₂-like phase at pressures of 60–80 GPa in a laser-heated diamond anvil cell. To provide definitive information about the nature of the natural “α-PbO₂ phase,” we recovered a small sample from the Shergotty meteorite, obtained powder X-ray diffraction patterns, and performed a Rietveld refinement of the structure. The resulting cell parameters and space group are a = 4.097(1) Å, b = 5.0462(9) Å, c = 4.4946(8) Å, and Pbcn. The structure refinement confirms that this sample does have the α-PbO₂ structure.