Rocks are one of nature’s tools for trapping carbon dioxide from air and permanently locking it away. The silicate minerals found in certain rocks react with carbon dioxide and convert it into solid carbonates. But the process, known as weathering, takes tens of thousands of years.

Stanford University chemists have now come up with a practical, low-cost way to sequester carbon dioxide using crushed rocks. They use a conventional kiln to transform silicate minerals into reactive materials that can quickly pull carbon from the atmosphere and store it. The process takes about half the energy of carbon dioxide capture with leading direct air capture technologies, the researchers report in the journal Nature.

Carbon capture projects that harness the natural process of mineralization are already underway around the world. Pulverizing rocks such as olivine, which contain magnesium silicate, speeds up its reaction with carbon dioxide. So some startups and researchers are looking to grind rocks almost to dust and spread them on farmland. Other startups are injecting captured carbon dioxide into peridotite rock formations and speeding up mineralization.

Yuxuan Chen and Matthew Kanan of Stanford have taken a different approach that leads to mineralization of carbon dioxide in weeks. They took inspiration from the established technique for cement production. That involves heating limestone, or calcium carbonate, to convert it into calcium oxide, which is then mixed with sand.

For their method, the research duo heats calcium oxide and magnesium silicate. When they heat the mixture to 1400°C, they get calcium silicate and magnesium oxide. Both of these are minerals that react very quickly with carbon dioxide in the air.

The researchers were able to produce around 15 kilograms of calcium silicate and magnesium oxide a week. To test the carbon capture ability of the minerals, they exposed the wet minerals to air. The minerals captured carbon dioxide over a time period of weeks to months, which is still thousands of times faster than natural rock weathering.

The magnesium silicate could come from rocks such as olivine, which are commonly found across the globe. They could also come from mine waste. “Each year, more than 400 million tons of mine tailings with suitable silicates are generated worldwide, providing a potentially large source of raw material,” Chen said in a press release. “It’s estimated that there are more than 100,000 gigatons of olivine and serpentine reserves on Earth, enough to permanently remove far more carbon dioxide than humans have ever emitted.”

The researchers’ energy calculations show that the process could require less than 1 megawatt-hours of energy per metric ton of carbon dioxide removed. That energy could be sustainable if, in the future, the kilns could be run on renewable electricity instead of burning fossil fuels.

Source: Matthew Kanan et al, Thermal Ca²⁺/Mg²⁺ exchange reactions to synthesize CO₂ removal materials, Nature, 2025.

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