Even with massive advances in clean technology and global adoption, the world will be burning fossil fuels for the next 50 years, perhaps far longer. Despite the explosive growth in renewable energy, we are still investing billions of dollars in infrastructure to burn many more decades of oil, gas, and coal.

That’s one reason everyone from utilities to environmental groups are pushing for carbon capture and storage. Although still untested on a scale large enough to avert severe climate change, underground rock formations can absorb or store as much greenhouse gas pollution as our power plants put out in a year. Keeping it there safely and economically is a challenge. One way may be to turn the emissions themselves into rocks.

One way to keep emissions underground safely and economically is to turn the emissions themselves into rocks.

Iceland, on the heels of other pilot projects around the world, has started to pump its own CO2 emissions underground. Diverting the gas from the 300 MW Hellisheioi Power Station, Iceland’s CarbFix project is attempting to turn its CO2 (dissolved as carbonic acid in water) into limestone through subterranean chemistry.

CarbFix is injecting its CO2 emissions into volcanic basalt, where it (hopefully) leaches minerals from the surrounding volcanic basalt to form new rock. If successful, and affordable, power plants around the world could point their greenhouse gasses into these underground formations and create new limestone–the same thing that makes up coral reefs–from their emissions.

“The capacity of these rocks, the storage capacity, could be very very large,” says Jurg Matter, a geochemistry professor at Columbia University, in Scientific American. Although mineralization happens naturally, the test projects are deliberating speeding up the process by concentrating carbon emissions in rock with the right chemical composition (it’s located everywhere from the U.S. to Siberia and also beneath the ocean).

The capacity of these rocks, the storage capacity, could be very very large.

Although Iceland is not the only country testing this technology, experiments underway in Australia and the U.S. remain expensive and technically challenging. One of them is the Big Sky Carbon Sequestration Partnership, according to MIT. The initiative includes a six-state, 85,000-square-mile area including Idaho, Montana, Wyoming, South Dakota, Washington, and Oregon theoretically capable of storing enormous amounts of CO2. A pilot program in southeast Washington has plans to start injecting CO2 in the spring of 2012 (its current status is available here)

Even with the chemistry, and technology, to turn carbon into rock is unsettled science, but its potential is so enormous that it may prove to be a massive storehouse of our carbon emissions. For now, as with most experimental technologies, costs are still sky-high: CarbFix project’s pilot project has spent $11 million to sequester its first 2,000 tons of CO2, even though researchers estimate the cost may fall to less than $10 per ton. Commercial deployment also seems decades away.