Nitrogen and hydrogen aggregation in natural octahedral and cuboid diamonds

• Published in: GEOCHEMICAL JOURNAL Vol. 51; no. 2; pp. 181 - 192
• Main Authors: Zedgenizov, D. A., Kalinin, A. A., Kalinina, V. V., Palyanov, Yu. N., Shatsky, V. S.
• Format: Journal Article
• Language: English
• Published: GEOCHEMICAL SOCIETY OF JAPAN 01.01.2017
• Subjects: aggregation; annealing; cuboid; defects; diamond; HP-HT treatment; hydrogen; nitrogen
• ISSN: 0016-7002; 1880-5973
• DOI: 10.2343/geochemj.2.0452

Transformations of nitrogen and hydrogen defects in natural octahedral and cuboid diamonds after multi-stage annealing at P = 6 GPa and T = 2200°C are presented. It has been observed that nitrogen aggregation from A- to B-defects in octahedral diamonds has gradually increased. This transformation of nitrogen has proceeded more rapidly in cuboid diamonds. One may confirm that most of the cuboid diamonds characterized by a low nitrogen aggregation state were not annealed over a long period at mantle conditions and their formation occurred shortly before transportation to the Earth’s surface. Unlike octahedral diamonds, cuboid diamonds show a considerable increase in the intensity of the primary hydrogen-related peaks after the annealing, thus implying involvement of sites to which the hydrogen can bond and become IR-active, but these sites are simply not available in the octahedral diamonds. The magnitude to which peak 3107 cm–1 is increased after annealing has been found to be correlated with the total nitrogen content in cuboid diamonds. This supports the suggestion that the vibrational system with a primary line at 3107 cm–1 corresponds to a C-H vibration bonded to some form of aggregated nitrogen.