Recent molecular simulations have revealed unexpected new understanding of how graphite and diamond grow out of liquified carbon. Each of these discoveries upend decades worth of consensus assumptions about these materials. Under the guidance of Davide Donadio, a research team used simulations to learn some pretty thrilling things. They discovered that high-pressure graphite can crystallize spontaneously, and this is true even up to 15 GPa—an environment in which diamond typically forms. With this research, we’ve captured the circumstances that trigger the formation of two very different types of carbon. It improves our perception of the deep carbon cycle and its profound effects on Earth’s climate and geology.
The research team, under the direction of Tianshu Li, a George Washington University civil and environmental engineering professor, set up model runs with different pressures. They validated these models from 5 to 30 GPa. They tracked the solidification of molten carbon as it crystallizes from similar near 5,000 Kelvin (K) down to 3,500 K. The implications from this study are that graphite commonly nucleates according to Ostwald’s step rule. This implies that crystallization can happen via the route of intermediate metastable phases, rather than by the direct route to the thermodynamically stable diamond structure.
Insights from Molecular Simulations
Donadio’s team used direct molecular dynamics to conduct large scale all-atom molecular simulations. They did this by fixing pressures of 15 and 15.5 GPa, while maintaining a temperature of 3,650 K. Through this approach, the researchers obtained an atomistic view of how both graphite and diamond crystallize from molten carbon under extreme conditions.
Researchers found that graphite can crystallize ahead of diamond stably, even in stable environments. This surprising finding further illuminates the dynamic and often complicated nature of crystallization processes. As noted by Tianshu Li, “The liquid carbon essentially finds it easier to become graphite first, even though diamond is ultimately more stable under these conditions.” This unique phenomenon emphasizes the importance of understanding the pathways that result in crystallization. It’s equally important that we grasp how these end products are produced.
Implications for Natural Diamond Formation
The study’s findings offer important clues as to why the geological formation of natural diamonds is such a rare process. As Donadio pointed out, “The work accounts for the presence of [graphite] where you might not expect it.” This suggests that the extreme conditions required for diamond formation are likely conducive to crystallization of graphite instead.
These findings help to reveal the highly complex deep carbon cycle. This cycle is one of the main drivers of Earth’s long-term climate and geological activity. Their study goes on to explain how these transformations happen. These results further our understanding of how carbon behaves deep within Earth’s interior.
Publication Details
The results of this groundbreaking study were published in a paper titled “Metastability and Ostwald step rule in the crystallisation of diamond and graphite from molten carbon.” Access the original research published via phys.org on July 9, 2025, DOI 10.1038/s41467-025-61674-5 Co-authors Margaret L. Berrens, Wanyu Zhao and Shunda Chen all played a part in creating this landmark work.