Olivine: Carbon Eater?

A simple rock is being put forth as the solution to global warming.

March 07, 2015

Olivine (n.): a magnesium-iron silicate that absorbs carbon dioxide from the air.

Humans have been trying to save beaches for decades. But the situation could soon turn on its head: Someday, beaches may save us. Did I just blow your mind?

A small group of geochemists in northern Europe is convinced that the solution to climate change—or at least part of the solution—is to use natural substances to absorb the carbon dioxide we've already emitted into the atmosphere. There are several minerals capable of this feat, but the one gaining the most attention is olivine. It’s a magnesium-containing crystal found in igneous rocks. One pound of the stuff can absorb as much as one pound of carbon dioxide from the air, under ideal circumstances.

Photo: Steve DunleavyGreen Sand Beach in Hawaii is so named for the olivine crystals deposited along its shore.

That last bit—the part about ideal circumstances—is the teensy-weensy problem. For olivine to work its magic most efficiently, it has to be broken into small bits. The more surface area exposed to the air, the faster carbon dioxide can be absorbed. Unfortunately, naturally occurring olivine isn’t always broken into small granules, which means we’d have to crush it. And breaking rocks takes a tremendous amount of energy. As long as we’re not going to bring back the chain-gang system of the early 20th century, we would have to burn fossil fuels, to grind up the rocks, to absorb the carbon from the fossil fuels we burned. In other words, we’d be running to stand still. (By the way, the state of Alabama ordered inmates to break rocks as recently as 1995, even though the state had no use for broken rocks. It’s not relevant to olivine or climate change—I just thought you’d be interested.)

Transportation would also be an issue. Offsetting even a third of global carbon emissions would require five gigatonnes of olivine granules. (That’s a five with nine zeroes.) It can’t just sit in a pile next to the olivine-crushing plant—we’d have to spread it over all the world’s beaches, agricultural fields, sandboxes, etc. How would we move all that olivine? In trucks that burn fossil fuels. Uh oh.

Left alone, olivine granules form a crust that blocks CO2 absorption, so they must be constantly agitated to keep absorbing carbon dioxide. That’s why sandboxes and farms are good places—there are often people and machinery passing through and moving the olivine around. When spread across a beach, olivine spends its days tumbling in the surf.

But what about all that dust generated by the crushing process and released from constant agitation in fields and sandboxes—is it bad for human or animal health? If large amounts of olivine get into the oceans, will it be harmful to aquatic ecosystems? There are many more questions to be answered.

Olivine is an intriguing tool in the fight against climate change, but it’s far behind some other technologies, like solar panels and windmills. Maybe we should start with those. These rocks aren’t going anywhere.

onEarth provides reporting and analysis about environmental science, policy, and culture. All opinions expressed are those of the authors and do not necessarily reflect the policies or positions of NRDC. Learn more or follow us on Facebook and Twitter.

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