El Goresy A, Chen M, Dubrovinsky L, Gillet P, Graup G
Max-Planck-Institut für Chemie, J. Joachim-Becher-Weg 27, 55128 Mainz, Germany.
Science. 2001 Aug 24;293(5534):1467-70. doi: 10.1126/science.1062342.
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) degrees; space group P2(1)/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 degrees C.
我们报告了在德国里斯陨石坑受冲击的片麻岩中发现一种超致密的金红石后多晶型二氧化钛。微观诊断特征是在反射光下交叉偏振器中强烈的蓝色内部反射。X射线衍射研究揭示了一种单斜晶格，与斜锆石ZrO2多晶型同构，并且钛阳离子与七个氧阴离子配位。晶胞参数如下：a = 4.606(2)埃，b = 4.986(3)埃，c = 4.933(3)埃，β（c轴与a轴之间的夹角）= 99.17(6)度；空间群P2(1)/c；密度 = 4.72克每立方厘米，其中括号中的数字是最后一位有效数字的标准偏差。这个相比金红石密度高11%。该矿物对X射线辐照敏感，并且倾向于转变为金红石。在受冲击岩石中存在斜锆石型TiO2表明峰值冲击压力在16至20吉帕斯卡之间，并且冲击后温度远低于500摄氏度。
