title: A monoclinic post-stishovite polymorph of silica in the shergotty meteorite
abstract: A post-stishovite phase of silica was identified in the Shergotty meteorite by x-ray diffraction and field emission scanning electron microscopy. The diffraction pattern revealed a monoclinic lattice, similar to the baddeleyite-structured polymorph with the cell parameters a = 4.375(1) angstroms, b = 4.584(1) angstroms, c = 4. 708(1) angstroms, beta= 99.97(3), rho = 4.30(2) grams per cubic centimeter, where the numbers in parentheses are the maximum deviations. Transmission electron microscopy investigations indicate the presence of the alpha-lead dioxide-like polymorph, stishovite, and secondary cristobalite in the same silica grain. The mixture of high-density polymorphs suggests that several post-stishovite phases were formed during the shock event on the Shergotty parent body.
authors.affiliation: Max-Planck-Institut fur Chemie, J.-Becher-Weg 27, D-55128 Mainz, Germany. Theoretical Geochemistry Program, Institute of Earth Sciences, Uppsala University, S-75236, Uppsala, Sweden. Department of Geology, Arizona State University, Tempe, A.
authors.lastname: El Goresy A
authors.initials: L
authors.lastname: Dubrovinsky
authors.initials: TG
authors.lastname: Sharp
authors.initials: SK
authors.lastname: Saxena
authors.initials: M
authors.lastname: Chen