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Science 24 August 2001:
Vol. 293. no. 5534, pp. 1467 - 1470
DOI: 10.1126/science.1062342
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Reports

An Ultradense Polymorph of Rutile with Seven-Coordinated Titanium from the Ries Crater

Ahmed El Goresy,1* Ming Chen,1 Leonid Dubrovinsky, Philippe Gillet, Günther Graup1

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 polarizers in reflected light. X-ray diffraction studies revealed a monoclinic lattice, isostructural with the baddeleyite ZrO2 polymorph, and the titanium cation is coordinated with seven oxygen anions. The cell parameters are as follows: a = 4.606(2) angstroms, b = 4.986(3) angstroms, c = 4.933(3) angstroms, beta  (angle between c and a axes) = 99.17(6)°; space group P21/c; density = 4.72 grams per cubic centimeter, where the numbers in parentheses are standard deviations in the last significant digits. This phase is 11% denser than rutile. The mineral is sensitive to x-ray irradiation and tends to invert to rutile. The presence of baddeleyite-type TiO2 in the shocked rocks indicates that the peak shock pressure was between 16 and 20 gigapascals, and the post-shock temperature was much lower than 500°C.

1 Max-Planck-Institut für Chemie, J. Joachim-Becher-Weg 27, 55128 Mainz, Germany. 2Guangzhou Institute of Geochemistry, Chinese Academy of Science, Guangzhou, 510640, China. 3Theoretical Geochemistry Program, Institute of Earth Sciences, Uppsala University, 75236 Uppsala, Sweden. 4Laboratoire de Sciences de la Terre, Ecole Normale Supérieur de Lyon, 69364 Lyon, France.
*   To whom correspondence should be addressed. E-mail: goresy{at}mpch-mainz.mpg.de

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
High-pressure mineral assemblages in shocked meteorites and shocked terrestrial rocks: Mechanisms of phase transformations and constraints to pressure and temperature histories.
P. Gillet, A. El Goresy, P. Beck, and M. Chen (2007)
Geological Society of America Special Papers 421, 57-82
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{alpha}-PbO2-type nanophase of TiO2 from coesite-bearing eclogite in the Dabie Mountains, China--Comment.
J. Chen and Z. Fu (2006)
American Mineralogist 91, 1699-1700
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A shock-induced polymorph of anatase and rutile from the Chesapeake Bay impact structure, Virginia, U.S.A..
J. C. Jackson, J. W. Horton Jr., I-M. Chou, and H. E. Belkin (2006)
American Mineralogist 91, 604-608
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In situ X-ray diffraction study of phase transitions of FeTiO3 at high pressures and temperatures using a large-volume press and synchrotron radiation.
L. C. Ming, Y.-H. Kim, T. Uchida, Y. Wang, and M. Rivers (2006)
American Mineralogist 91, 120-126
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{alpha}-PbO2-type nanophase of TiO2 from coesite-bearing eclogite in the Dabie Mountains, China.
X. Wu, D. Meng, and Y. Han (2005)
American Mineralogist 90, 1458-1461
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