Diamonds are a valuable tool for petrologists in order to study the lithospheric mantle. Diamond’s unique material properties enable it to act as a record of the conditions within the mantle from which diamonds grow, through mineral inclusions and crystallographic defects within the lattice. One impurity often observed is hydrogen, with the most common form being the N3VH centre, seen in the IR spectra of many natural diamonds. Despite its ubiquity, it is not well understood. This work initially presents an attempt at quantification of the amount of hydrogen present in natural diamonds and how it relates to the amount of N3VH. The results suggest that most hydrogen within diamonds is not contained in the N3VH defect, with the concentrations observed over 20 times higher than predicted using IR alone. High-quality IR and UV-vis line scans are then used to interrogate the effect of hydrogen on the nitrogen aggregation sequence in diamonds, specifically using the concentration of N3, a minor aggregate. This enables generation of proportionality constants within each diamond and suggests that the primary formation mechanism of N3VH is through direct protonation of N3. A methodology is laid out for studying the availability of hydrogen within diamond-forming fluids through the study of the relative abundance of N3 and N3VH within a diamond. A minor IR peak at 3236 cm-1 is also investigated through comparison with other IR features, and some evidence is found for aggregated nitrogen and platelets in the defect structure.
|Date of Award||23 Mar 2021|
- The University of Bristol
|Supervisor||Simon C Kohn (Supervisor) & Richard A Brooker (Supervisor)|