Here’s what you’ll learn when you read this story:

• Dolomite is a mineral usually formed from limestone and magnesium, but while it’s common in nature, lab experiments have failed to replicate its growth.
• The issue with previous attempts to grow dolomite was that its layers of calcium and magnesium would often arrange themselves defectively.
• New research modeled dolomite growth with software, then used transmission electron microscopy to eliminate defects and speed up production.

Hundreds of millions of years ago, creatures living in primordial seas died and their remains drifted to the ocean floor. Sunken skeletal fragments and shells lying on shallow seabeds were compressed under extreme pressure for eons, eventually forming limestone. Sometimes, water rich in dissolved magnesium coursed through that limestone, recrystallizing it into calcium magnesium carbonate, a mineral otherwise known as dolomite.

Most dolomite occurs as dolostone, the amalgamation of ancient shell and bone which often glints with traces of other minerals, but dolomite crystals can occur on their own in sedimentary rocks and deposits from subsurface hydrothermal veins heated by flows of magma. While it’s commonly found in rocks over 100 million years old, newer growth is rare because of how it forms: crystals grow when atoms attach themselves to the surface of an existing crystal in a certain order.

Dolomite also contains magnesium, and when magnesium and calcium are compressed together over time, the two minerals end up attaching to previous layers randomly, causing structural defects that impede growth. Shifting tides and rain periodically wash away these defects, because unstable atoms that are misplaced in the crystal lattice are prone to dissolving in water. Otherwise, it would take around 10 million years to form just one layer of dolomite. That would have made dolomite nowhere near common enough to use in concrete and other construction, manufacturing, and industrial applications. For the same reasons, every attempt to grow dolomite in a lab has been unsuccessful for two centuries. But a team of researchers has finally figured out how to do it.

“The apparent contradiction between the massive deposits of dolomite in nature and its inability to grow from supersaturated solutions near ambient conditions is a long-standing mystery known as the ‘dolomite problem,’” said materials scientist Wenhao Sun of the University of Michigan’s Predictive Structure Materials Science (PRISMS) Center, who led a study recently published in Science.

Previous theories about why dolomite is so stubborn to form only led to more frustration. The solutions in which crystals grow need to be supersaturated with high levels of the elements required for the crystals to form in the first place. But, as scientists found, dolomite will refuse to precipitate even in supersaturated solutions at ambient temperatures in a lab. One unfortunate experiment involved trying to grow it from a solution that was saturated a thousand times over, but the process kept failing for a staggering 32 years.

To finally crack this decades-old problem, Sun and the PRISMS team trained software to model the flawed formation of dolomite. By predicting how much energy is needed for certain atomic arrangements to occur, and then using that information to determine how much energy future arrangements will need, the formation of dolomite could at least be simulated.

When dolomite growth was initially simulated at undiluted supersaturation, it showed the typical structural flaws from disorganized atoms. The team then moved on to fluctuating supersaturation that was modeled after natural dolomite deposits that are usually found in coastal areas and environments that receive precipitation. Too much water would make the solution undersaturated, but it would also wash away unstable atoms in the way of its growth, so when that excess water evaporated, the mineral would continue growing. Because Sun wanted to observe this actually happening, the PRISMS team collaborated with Hokkaido University researchers Yuki Kimura and Tomoya Yamazaki.

Kimura and Yamazaki had realized that a side effect of transmission electron microscopes was a plus for their quest to crystallize dolomite. The electron beams used by these microscopes for imaging can split water, creating an acid that is corrosive to crystals. But what is often catastrophic for imaging purposes has the upside of dissolving obstructive defects in dolomite, and both research teams took advantage of this phenomenon by repeatedly pulsing an electron beam at the solution for two hours to zap away anything that was out of place. Under this treatment, defects in crystals grow more slowly and also dissolve faster because they are higher in energy.

Together, the teams succeeded in growing 300 layers of dolomite, which are still invisible to the naked eye at about 100 nanometers or 1/250,000th of an inch, but that result far outdoes previous experiments, which could never achieve more than five layers. Growing dolomite will no longer need a timescale that sees several mass extinctions come and go before there’s enough to supply the industries that need it. In the future, applications that use dolomite such as batteries, semiconductors, and solar panels could benefit from this breakthrough in speeding up its production.

“Defective regions are higher in energy than pristine regions and thus will dissolve faster and grow slower, which over time results in a net flux of atoms from defective to pristine sites,” Sun said. “By deliberately introducing periods of mild undersaturation, one can facilitate the dissolution of defects, whose dissolution would otherwise proceed very slowly under constant high supersaturation.”