Synchrotron infrared and Raman spectroscopy of microdiamonds from Erzgebirge, Germany

Metamorphic diamonds from the Erzgebirge, Germany have been investigated using synchrotron infrared absorption, Raman scattering, and fluorescence spectroscopy. Infrared absorption features associated with C–C, C–H bonds, molecular H2O, OH− and CO32− radicals, and N-impurities were observed. The results suggest that a carbon–oxygen–hydrogen (COH) supercritical fluid is the most probable concept to explain the origin of diamonds from ultrahigh-pressure metamorphic terranes (UHPM). Investigation of the nitrogen impurities suggests that the Erzgebirge diamonds belong to the Type 1b-1aA, which is similar to metamorphic diamonds from the Kokchetav massif of Kazakhstan and the Western Gneiss Region of Norway, and differentiates them from other nitrogen-bearing diamonds from kimberlitic sources (Type 1aAB). The occurrence of nitrogen impurities as single atoms in the crystal lattice implies that the Erzgebirge diamonds had a short residence at high-pressure and high-temperature, which therefore suggests a possibility for very fast exhumation. Both infrared and previous studies of nanoinclusions using a transmission electron microscope support a concept of diamond crystallization from a COH rich supercritical fluid.