The 'Dolomite Problem' Has Baffled Scientists For Centuries—And Now They've Solved It
Although dolomite is relatively plentiful in rocks older than 100 million years, scientists have been unable to replicate the geologic process in the lab—until now.
Using a transmission electron microscope, scientists “dissolved” defects as they formed on the dolomite crystal, speeding up its growth process.
Understanding how these minerals form could unlock advancements in growing the necessary materials for semiconductors.
You can find dolomite all over the world. It’s a calcium magnesium carbonate found in the Dolomite Mountains in northern Italy (obviously), but also at Niagara Falls in North America and the White Cliffs of Dover in the U.K. Altogether, this useful construction mineral makes up some two percent of the Earth’s crust.
But in contrast to its relative natural abundance, scientists have failed to recreate dolomite in the lab for nearly two centuries, leading to what experts call the “Dolomite Problem.” But new work from scientists at the University of Michigan (UM) and Hokkaido University in Sapporo, Japan seems to have finally solved this geologic conundrum by leveraging proprietary software and dissolving crystalline defects with an electron beam. The results of the study were published in the journal Science this past November.
“In the past, crystal growers who wanted to make materials without defects would try to grow them really slowly…our theory shows that you can grow defect-free materials quickly, if you periodically dissolve the defects away during growth,” Wenhao Sun, UM scientist and the corresponding author, said in a press statement. “If we understand how dolomite grows in nature, we might learn new strategies to promote the crystal growth of modern technological materials.”
Dolomite is usually found in rocks older than 100 million years, meaning that this mineral take a long time to form. According to the researchers, this slow growth rate can be attributed to how dolomite’s crystalline structure forms. The mineral’s growth edge is made of alternating rows of calcium and magnesium, and in water, these elements randomly attach to the wrong places and prevent dolomite from forming. While the Earth has nearly infinite patience to wait out this slow growth (like, only one dolomite layer produced per 10 million years slow), humans—with their comparatively infinitesimally small lifespans—do not.
To figure out how to speed up this natural process, scientists needed to understand how these defects attach to the dolomite surface. Usually, this would take thousands of hours of supercomputing, but new UM software leverages a novel technique to complete these simulations “in 2 milliseconds on a desktop,” according to one researcher.
“Our software calculates the energy for some atomic arrangements, then extrapolates to predict the energies for other arrangements based on the symmetry of the crystal structure,” UM associate research scientist and co-author Brian Puchala, one of the software’s lead developers, said in a press statement.
Once the team from UM understood how dolomite grows over these long geologic timescales, the scientists from Hokkaido University took the reins. Although transmission electron microscopes are usually used for imaging incredibly small things, they also have a useful byproduct that makes them perfectly suited for this particular experiment.
“Electron microscopes usually use electron beams just to image samples,” Hokkaido University’s Yuki Kimura said in a press release. “However, the beam can also split water, which makes acid that can cause crystals to dissolve. Usually this is bad for imaging, but in this case, dissolution is exactly what we wanted.”
Kimura’s team placed a dolomite sample in a calcium/magnesium solution and pulsed an electron beam 4,000 times over two hours. The resulting acid effectively dissolved away any defects and allowed dolomite to grow roughly 100 nanometers. This equates to roughly 300 layers of dolomite, which is 60 times more than has ever been grown in a lab before. Hopefully, unlocking the secrets of dolomite growth could help future scientists understand the geologic processes of other minerals, especially those used in semiconductors.
Every once in a while, impatience pays off.
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