Dolomite Crystal Growth Demands Saturation Cycle Conditions

Addressing the long-standing "dolomite problem," an oddity that has vexed scientists for nearly 200 years, researchers report that dolomite crystals require cycling of saturation conditions to grow. The findings provide new insights into how dolomite is formed and why modern dolomite is primarily found in natural environments with pH or salinity fluctuations. Dolomite – a calcium magnesium carbonate – is one of the major minerals in carbonate rocks, accounting for nearly 30% of the sedimentary carbonate minerality in Earth's crust. However, despite its geological abundance, dolomite does not readily grow under laboratory conditions, hindering the study of the mineral. For two centuries, scientific efforts have failed to precipitate dolomite in the laboratory near ambient conditions. The apparent contradiction between the massive deposits of dolomite in nature and its inability to grow even in supersaturated solutions under ambient conditions has resulted in the so-called dolomite problem. Here, using atomistic simulations of dolomite, Joonsoo Kim and colleagues make a discovery that informs this issue. Kim et al. used density function theory and kinetic Monte Carlo crystal growth simulations to show that cycles of saturation conditions are needed to promote dolomite crystal growth in the laboratory. According to the simulation's predictions, frequent cycling of a solution between supersaturation and undersaturation can speed up dolomite growth by up to 10 million times – a process that may be paramount for producing the large amounts of dolomite on Earth's surface. The authors validated their predictions using a transmission electron microscope to observe bulk dolomite crystal growth in situ under fluctuating saturation conditions. "The findings of Kim et al. raise many questions about how geochemical fluctuations occur in the natural world over geological timescales and what factors influence the process," writes Juan Manuel García-Ruiz in a related Perspective.