The Rock That Vacuums Up Carbon DioxideS

There's an igneous rock called peridotite that can sponge carbon dioxide out of the atmosphere and store it in mineral form. Weirdly, almost no one is talking about it.

Peridotite isn't one of the better-known rocks, but it's got a number of properties that could place it right at the center of the climate-change conversation. Some quick facts:

1) Peridotite is one of the most abundant rocks in the Earth's mantle, and exists in surface deposits all over the world.

2) When peridotite reacts with carbon dioxide, it forms a solid mineral not unlike limestone, trapping the carbon in the molecular structure of the rock.

3) Geologists believe there's enough peridotite in Oman alone to absorb four billion tons of carbon each year.

4) Columbia University recently received a modest federal grant to study peridotitic reactions. Aside from that, practically no one has expressed any interest in the rock's potential.

An excellent essay by Sam Kornell in Miller-McCune goes into more detail about peridotite's odd elision from the environmentalist dialogue. The process of storing greenhouse gases in some form that won't clog the atmosphere, known as "sequestration," is something scientists and policymakers have been talking about for a while. That discussion, though, is largely focused on capturing emissions as they're produced and storing them as a gas, an expensive stopgap measure that isn't guaranteed to work.

Last year, a research team at Columbia's Lamont-Doherty Earth Observatory determined that the natural peridotite reserves in Oman are removing at least ten thousand tons of atmospheric carbon each year, and maybe as much as a hundred thousand tons. It's not enough to offset the annual thirty billion tons of carbon that human activity introduces into the atmosphere, but there's a lot more peridotite lying around, and whatever carbon gets incorporated into the rock structure will stay there for good.

The biggest problem with peridotite — and likely the reason more people haven't considered it as a possible supplement to emissions-reduction measures — is that the gas-to-solid reaction takes a long time to happen. Millennia, in fact. The Department of Energy briefly funded some research into speeding up this process in 2003, but the issue was dropped soon after. Sam Krevor, a doctoral student at Columbia, has said that there's no physical law preventing an expedited reaction process; all that's needed is the time, and the resources, to figure out a way to bring it about.

Since then, there's been little activity on the peridotite front until this past September, when about $300,000 of federal money went toward a Columbia study on carbon capture in minerals. According to a recent DoE press release, the project will look for carbonation catalysts and encourage positive-feedback cycles in peridotitic and basaltic rocks, and "support at least 2 graduate students during the research efforts." Three hundred grand isn't a huge amount of money, but if it gets two more people talking about the vast, untapped usefulness of these rocks, it's a start.

A Rock That Helps Out In a Hard Place [Miller-McCune]