Scientists are proposing a new way to make cement by replacing limestone with volcanic rocks like basalt, a shift they say could dramatically cut emissions tied to one of the world’s dirtiest industries.

Researchers from UC Santa Barbara and Brimstone Energy found that calcium-rich silicate rocks could be used to produce Portland cement, the world’s most widely used construction material, while using less energy and releasing far less carbon dioxide than conventional methods.

The cement industry currently contributes about 4.4 percent of global greenhouse gas emissions, largely because limestone releases massive amounts of CO2 when heated during cement production. The team argues that switching to silicate rocks could remove much of that carbon burden from the start.

“Cement barely registers in the public mind as a major driver of climate change, but the CO2 emissions from cement production are similar to all the world’s passenger cars,” said Jeff Prancevic, a geologist at UC Santa Barbara.

The researchers calculated that cement made from silicate rocks could require less than 60 percent of the energy needed to process limestone while cutting associated carbon dioxide emissions by more than 80 percent.

Swapping out limestone

Traditional Portland cement production relies on limestone because it is rich in calcium and relatively easy to process. But limestone comes with a major drawback: it is packed with carbon.

“But limestone is half CO2,” Prancevic said, “which is released into the atmosphere during cement production.”

Current cement manufacturing requires heating limestone above 1,500°C to produce quicklime, a key ingredient in cement. During that process, carbon dioxide trapped inside the rock is released into the atmosphere. Researchers estimate that conventional production emits roughly 500 kilograms of CO2 per metric ton of cement, excluding emissions generated by the energy-intensive heating process itself.

To avoid this, the team investigated calcium-rich silicate rocks such as basalt and gabbro. Unlike limestone, these rocks contain little embedded carbon, allowing cement production to avoid a major emissions source.

Researchers also examined whether enough of these rocks exist to support global cement demand. Using geological maps, they concluded that basalt resources are abundant enough to sustain production for hundreds of thousands of years at current consumption rates.

“Not all of that basalt is easily accessible,” Prancevic said, “but the numbers suggest that calcium from basalt is virtually inexhaustible.”

Metals from one rock

Beyond lowering emissions, the researchers say silicate rocks could unlock broader industrial benefits because they contain metals that can be recovered during processing.

According to the team, basalt naturally contains iron and aluminum alongside calcium. The ratio of calcium and iron in basalt closely matches society’s combined demand for cement and steel production, potentially allowing multiple industrial materials to be sourced from the same feedstock.

The researchers found that even without process optimization, using existing industrial technologies and average grid electricity could still reduce carbon dioxide emissions by more than 25 percent compared to standard limestone-based production.

Still, the transition may face resistance because the cement industry is heavily optimized around limestone and Portland cement standards developed over more than a century.

“The construction industry is built around Portland cement, from design to placement to maintenance,” Prancevic said. “Even subtle changes in standards are painstakingly considered and are slow to be adopted.”

The researchers say one advantage of their approach is that it still produces standard Portland cement, allowing it to fit into existing supply chains and construction practices without requiring entirely new materials.

“This paper is really a call for other researchers to experiment with new technologies to accelerate cement decarbonization,” Prancevic said, “because there is the potential to solve a climate problem as big as cars simply by sourcing calcium from a different rock.”