Atmospheric carbon dioxide injected into volcanic rock as part of a pilot project in Iceland was almost completely mineralized, or converted to carbonate minerals, in less than two years, a new study shows. The results suggest that basaltic rocks may be effective sinks for storing carbon dioxide removed from the atmosphere. Atmospheric carbon dioxide can be sequestered by injecting it into rocks deep underground. However, to date, injection has largely been done in rocks depleted of the calcium-, magnesium-, and iron-rich silicate minerals required to convert this greenhouse gas into carbonate minerals. This creates a risk of carbon dioxide leakage. An alternative approach is to inject carbon dioxide into basaltic rocks, which are silicates and one of the most common rock types on Earth. Here, Juerg Matter and colleagues describe results from a recent pilot project, CarbFix, conducted in Iceland in which carbon dioxide was injected into wells that pass through basaltic lavas at depths between 400 and 800 meters. Using a suite of tracers, the authors determined that most of the injected carbon dioxide was mineralized in less than 2 years. Since carbonate minerals are stable, this approach is not as susceptible to the risk of carbon dioxide leakage, the authors say, meaning monitoring of basaltic storage sites could be significantly reduced. And because this technique relies mostly on water and porous basaltic rocks, both of which are widely available on continental margins in many parts of the world, scaling up will be feasible, the authors say.