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Two novel shock-induced very dense polymorphs of rutile in suevite from the Ries Crater, Germany: Implications for peak-shock pressures and post-shock temperatures.

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Abstract

We report two new natural shock-induced very dense polymorphs of rutile from suevites of the Ries Crater, Germany. This finding sets entirely new parameters for a robust estimation of peak-shock pressures and post-shock temperatures not accounted for before.

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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, β= 99.97(3), ρ = 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 α-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.