Murri Mara, Smith Rachael L, McColl Kit, Hart Martin, Alvaro Matteo, Jones Adrian P, Németh Péter, Salzmann Christoph G, Corà Furio, Domeneghetti Maria C, Nestola Fabrizio, Sobolev Nikolay V, Vishnevsky Sergey A, Logvinova Alla M, McMillan Paul F
Department of Earth and Environmental Sciences, University of Pavia, Via A. Ferrata 1, 27100, Pavia, Italy.
Department of Chemistry, University College London, 20 Gordon Street, London, WC1H 0AJ, UK.
Sci Rep. 2019 Jul 17;9(1):10334. doi: 10.1038/s41598-019-46556-3.
Diamond is a material of immense technological importance and an ancient signifier for wealth and societal status. In geology, diamond forms as part of the deep carbon cycle and typically displays a highly ordered cubic crystal structure. Impact diamonds, however, often exhibit structural disorder in the form of complex combinations of cubic and hexagonal stacking motifs. The structural characterization of such diamonds remains a challenge. Here, impact diamonds from the Popigai crater were characterized with a range of techniques. Using the MCDIFFaX approach for analysing X-ray diffraction data, hexagonality indices up to 40% were found. The effects of increasing amounts of hexagonal stacking on the Raman spectra of diamond were investigated computationally and found to be in excellent agreement with trends in the experimental spectra. Electron microscopy revealed nanoscale twinning within the cubic diamond structure. Our analyses lead us to propose a systematic protocol for assigning specific hexagonality attributes to the mineral designated as lonsdaleite among natural and synthetic samples.
钻石是一种具有巨大技术重要性的材料，也是财富和社会地位的古老象征。在地质学中，钻石是深部碳循环的一部分形成的，通常呈现高度有序的立方晶体结构。然而，冲击钻石往往以立方和六方堆积模式的复杂组合形式表现出结构无序。此类钻石的结构表征仍然是一项挑战。在此，利用一系列技术对来自波皮盖陨石坑的冲击钻石进行了表征。使用MCDIFFaX方法分析X射线衍射数据，发现六方度指数高达40%。通过计算研究了六方堆积量增加对钻石拉曼光谱的影响，发现与实验光谱趋势高度吻合。电子显微镜揭示了立方钻石结构内的纳米级孪晶。我们的分析使我们提出了一个系统方案，用于在天然和合成样品中为被指定为六方碳的矿物指定特定的六方度属性。
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