Turning Carbon Dioxide Into Rock, and Burying It

HENGILL, Iceland — In a cramped work trailer not far from Iceland’s largest geothermal power plant, a researcher pored over a box of core samples — cylinders of rock that a drilling rig had pulled from deep underground just a few minutes before.

In a test that began in 2012, scientists had injected hundreds of tons of water and carbon dioxide gas 1,500 feet down into layers of porous basaltic rock, the product of ancient lava flows from the nearby Hengill volcano. Now the researcher, Sandra Snaebjornsdottir, a doctoral student at the University of Iceland, was looking for signs that the CO₂ had combined with elements in the basalt and become calcite, a solid crystalline mineral.

In short, she wanted to see if the gas had turned to stone.

“We have some calcites here,” she said, pointing to a smattering of white particles in the otherwise dark gray rock samples. “We might want to take a better look at them later.”

Ms. Snaebjornsdottir and her colleagues are certain that the process works, but the cores — eventually hundreds of feet of them — will undergo detailed analysis at a laboratory in Reykjavik, Iceland’s capital, to confirm that the calcites resulted from the CO₂ injection.