An ultradense polymorph of rutile with seven-coordinated titanium from theRies crater

We report the discovery of an ultradense post-rutile polymorph of titanium dioxide in shocked gneisses of the Ries crater in Germany. The microscopic diagnostic feature is intense blue internal reflections in crossed polarize rs in reflected light. X-ray diffraction studies revealed a monoclinic latt ice, isostructural with the baddeleyite ZrO2 polymorph, and the titanium ca tion is coordinated with seven oxygen anions. The cell parameters are as fo llows: a = 4.606(2) angstroms, b = 4.986(3) angstroms, c = 4.933(3) angstro ms, beta (angle between c and a axes) = 99.17(6)degrees; space group P2(1)/ c; density = 4.72 grams per cubic centimeter, where the numbers in parenthe ses are standard deviations in the last significant digits. This phase is 1 1% denser than rutile. The mineral is sensitive to x-ray irradiation and te nds to invert to rutile. The presence of baddeleyite-type TiO2 in the shock ed rocks indicates that the peak shock pressure was between 16 and 20 gigap ascals, and the post-shock temperature was much lower than 500 degreesC.