For more than two centuries, scientists have tried and failed to grow dolomite in the lab under conditions thought to match the way dolomite forms in nature. Recent research has finally changed that. Researchers at the University of Michigan and Hokkaido University in Sapporo have successfully developed a new theory based on detailed atomic simulations.
Their research solves a long-standing geological puzzle known as the “dolomite problem.” Dolomite is a widespread mineral found in iconic locations such as Italy’s Dolomite Mountains, Niagara Falls, and Utah’s Hoodoo. It is abundant in rocks that are more than 100 million years old, but it is rarely seen forming in more recent environments.
“Understanding how dolomite grows in nature may teach us new strategies for promoting crystal growth in modern technological materials,” said Wenhao Sun, early career professor of materials science and engineering at Dow University and corresponding author of the paper published in Science.
Reasons why dolomite grows slowly
Important advances have been made in understanding what is destroyed as dolomite forms. In water, minerals typically grow as atoms attach themselves to the surface of crystals in an orderly manner. Dolomite behaves differently because its structure is made of alternating layers of calcium and magnesium.
As the crystal grows, these two elements often stick together randomly instead of lining up correctly. This creates structural deficiencies that prevent further growth. As a result, the process becomes very slow. At that rate, it could take up to 10 million years to form a single, orderly layer of dolomite.
Naturally built-in reset mechanism
Researchers found that these defects were not permanent. Misaligned atoms are less stable and more likely to dissolve when exposed to water. In the natural environment, cycles such as rainfall and tides repeatedly wash away these defective areas.
Over time, this process cleans the surface and allows new, well-placed layers to form. Rather than taking millions of years to form a single layer, dolomite accumulates gradually over much shorter intervals. Over long geological periods, large deposits are formed that are found in ancient rock formations.
Simulation of crystal growth at the atomic level
To test their idea, the team needed to model how atoms interact as a form of dolomite. This requires calculating the energy involved in the countless interactions between electrons and atoms, which is usually very difficult in terms of computational power.
Researchers at UM’s Predictive Structural Materials Science (PRISMS) Center have developed software to simplify this task. Calculate the energy of a specific atomic arrangement and predict other atomic arrangements based on the symmetries of the crystal structure.
“Our software calculates the energy of some atomic arrangements and extrapolates to predict the energies of other atomic arrangements based on the symmetries of the crystal structure,” said Brian Puchala, one of the software’s lead developers and an associate research scientist in UM’s Department of Materials Science and Engineering.
This approach made it possible to simulate dolomite growth over a timescale that reflects real geological processes.
“Each atomic step typically takes more than 5,000 CPU hours on a supercomputer. Now, the same calculation can be performed on a desktop in 2 milliseconds,” said Joonsoo Kim, a doctoral student in materials science and engineering and lead author of the study.
Laboratory experiments confirm theory
Even today, the natural environments in which dolomite forms frequently involve cycles of flooding followed by drying, supporting the team’s theory. However, direct experimental evidence was still needed.
The evidence comes from Yuki Kimura, a professor of materials science at Hokkaido University, and Tomoya Yamazaki, a postdoctoral fellow in his lab. They used the unusual properties of a transmission electron microscope to recreate the process.
“An electron microscope typically uses an electron beam just to image the sample,” Kimura says. “But the beam can also split the water, which produces acids that cause the crystals to dissolve. Usually this has a negative effect on imaging, but in this case the dissolution is exactly what we wanted.”
The research team placed small dolomite crystals in a solution containing calcium and magnesium. The electron beam was then pulsed 4,000 times over two hours to repeatedly dissolve any defects that formed.
After this process, the crystals grew to about 100 nanometers, or about 1/250,000th of an inch. The growth represented approximately 300 dolomite layers. Previous experiments have never produced more than 5 layers.
Impact on modern technology
Solving the dolomite problem is more than just explaining a geological mystery. It also provides insight into how to control crystal growth in advanced materials used in modern technology.
“In the past, crystal growers who wanted to create defect-free materials tried to grow them very slowly,” Sun said. “Our theory shows that defect-free materials can be grown quickly if defects are periodically dissolved and removed during growth.”
The concept could help improve the production of semiconductors, solar panels, batteries, and other high-performance technologies.
This research was funded by the American Chemical Society PRF New Doctoral Investigator Grant, the U.S. Department of Energy, and the Japan Society for the Promotion of Science.
