New Study Explores Graphite's Role in Diamond Formation Dynamics

A groundbreaking study published on July 9, 2025, in *Nature Communications* reveals new insights into the crystallization processes of molten carbon, suggesting that graphite—commonly associated with pencils—can unexpectedly inhibit the formation of diamonds. Researchers from the University of California, Davis, and George Washington University employed advanced computational simulations to investigate how molten carbon crystallizes into either graphite or diamond under extreme temperature and pressure conditions similar to those found in Earth's interior.

The findings challenge long-held assumptions about diamond formation. According to Dr. Davide Donadio, a professor in the Department of Chemistry at UC Davis and the study's senior author, the research indicates that liquid carbon may more readily crystallize into graphite—despite diamond being the more stable form under certain conditions. "The advantage of simulations is that you can easily realize these extreme conditions without any special machinery," he explained, emphasizing the limitations of experimental setups to replicate such high pressures and temperatures.

The study utilized machine learning-powered molecular simulations to analyze the crystallization behavior of liquid carbon, revealing that at pressures ranging from 5 to 30 gigapascals (GPa) and temperatures between 5000 to 3500 Kelvin (K), graphite can form spontaneously in environments traditionally considered favorable for diamond formation. Co-author Dr. Tianshu Li, a professor of civil and environmental engineering at George Washington University, noted, "The liquid carbon essentially finds it easier to become graphite first, even though diamond is ultimately more stable under these conditions."

This unexpected crystallization alignment aligns with Ostwald's step rule, which posits that crystallization may occur through intermediate metastable phases rather than directly transitioning to the most stable form. The implications of this research extend beyond academic curiosity; they offer new perspectives on the deep carbon cycle that influences Earth's climate and geology over geological timescales.

Historically, the formation of natural diamonds has been rare, with many scientists puzzled by the inconsistencies observed in high-pressure carbon experiments. The study’s insights provide a framework to better understand these discrepancies and suggest that graphite's presence may be more significant in various geological contexts than previously acknowledged.

The research has broader implications for materials science, particularly in the synthesis of industrial diamonds. Improved understanding of the crystallization pathways could enhance the production of diamonds for specialized applications, such as quantum computing, where the precise control of crystal structure is paramount.

The study underscores the importance of continued research into the behavior of materials under extreme conditions, as advancements in this area could lead to technological innovations across various sectors. As Dr. Donadio concluded, "Crystallization is so fundamental for technology, and diamonds are extremely useful as materials. This work accounts for the presence of graphite where you might not expect it."

This research was supported by grants from the National Science Foundation, and co-authors Margaret L. Berrens, Wanyu Zhao, and Shunda Chen contributed significantly to the study's findings.