Internal diamond morphology: Raman imaging of metamorphic diamonds

Abstract

Confocal 2‐D and 3‐D Raman imaging of the Kokchetav metamorphic diamonds from different rock types reveals that these diamonds have a rather complex internal morphology. The diamond shows a strong change in the position of the diamond Raman line as well as the width of this line, which could be found both in the XY and in the YZ scan. These features indicate variations in the crystalline quality of the diamond. The broadest lines are located in the center of the octahedral diamond inclusion whereas the material close to the diamond–garnet interface shows smaller line widths. These features were also found for thermochemically extracted diamond crystals, which are not armored by host mineral, and in situ for inter‐ and intragranular diamond. Furthermore, host–garnet display no evidence for broadening or up‐shift of main Raman bands, indicating very low (below detection limit) residual strain. Thus the broadening and upshift of main diamond band do not relate to residual strain in inclusion–host systems. A comparison of Raman imaging results with cathodoluminescence images reveals that the distribution of defects, which cause the cathodoluminescence of diamond crystals, can be traced by Raman imaging. The 2‐D and 3‐D Raman imaging is a very powerful tool for study of internal morphology and growth pattern of metamorphic diamond, even it is a small crystal less than 10 µm in size. The growth pattern for octahedral diamond crystals from garnet–clinozoisite gneisses were obtained for the first time by Raman imaging. Copyright © 2015 John Wiley & Sons, Ltd.