Raman identification of lonsdaleite in Popigai impactites

Micro-Raman spectroscopy and X-ray diffraction method (XRD) were used to characterize impact carbonaceous rocks excavated from the Popigai crater (Siberia). The deconvolution of the first-order Raman spectra of the rocks containing different amounts of carbon phases (diamond, lonsdaleite and graphite) allowed the identification of lonsdaleite spectrum. The most intensive band at 1292-1303 cm(-1) was ascribed to A(1g) vibration mode of lonsdaleite, whereas the less intense band at 1219-1244 cm(-1) was attributed, in agreement with previously reported ab initio calculations, to E-2g vibration mode. The established correlation between the intensities of Raman and XRD peaks permits a rough estimation of lonsdaleite/diamond phase ratio in the impact rocks using micro-Raman measurements. The second-order Raman spectra of lonsdaleite-diamond rocks were recorded. Copyright (c) 2014 John Wiley & Sons, Ltd.