A new mechanism that may explain the formation of natural diamonds has been presented in Nature Communications this week. According to a new model, a drop in pH during water-rock interactions deep within the Earth is capable of leading to diamond precipitation.

Previously, the cause of diamond formation has been attributed to poorly-understood redox reactions associated with fluids or magmas at depth, but the role of pH changes has not been explored. Dimitri Sverjensky and colleagues use a theoretical approach to model the conditions under which diamonds might form, using hydrous fluids and elevated temperatures and pressures. By modelling how the fluids evolve during migration and how they interact with silicate rocks, the authors suggest that fluid-mineral reactions cause a decrease in pH, resulting in the right conditions for diamonds to be precipitated. This occurs without the redox changes that were previously invoked to explain diamond formation, although the previous theory may still be valid in some settings.

The new model could be useful for investigating different natural settings in which diamonds form, and may be expanded to include more sophisticated parameters. Eventually this kind of research may help to unravel the complicated history of fluids in the deep Earth through geological time.