For a modern-day climate scientist, this rock could be magical.
Humans release at least 35 billion tons of carbon dioxide into the atmosphere each year, which can be tough on the environment.
But what if, alchemy-like, we could take all that carbon dioxide and turn it into rock?
At Iceland's Hellisheidi power plant, that's what they've been trying to do.
Hellisheidi is a geothermal plant, which means it uses volcanically-heated water to run turbines, but the process isn't perfectly emission-free — it can bring up volcanic gases, including carbon dioxide.
And while the amount of those gases it generates are only a tiny fraction of what a coal plant would produce, the power plant still wanted to get rid of it.
So in 2012, they started a pilot program, Carbfix, to try putting that carbon back in the ground.
How do they do it?
They capture the plant's carbon dioxide, mix it with water, and inject it nearly a half-mile down into the volcanic basalt.
There, the carbon dioxide reacts with chemicals naturally found in the basalt and turns from a gas into chalky, white carbonate.
Some previous projects have tried pumping carbon dioxide into sandstone or aquifers, but that was essentially just hiding the carbon dioxide. This process transforms it.
That's great! But the truly amazing thing is that the process works hundreds of times faster than anyone predicted.
We knew this chemical reaction was theoretically possible, but previous studies guessed that it'd take hundreds, maybe even thousands, of years to work.
But Hellisheidi blew that timeline away. Within two years, 95% of the carbon dioxide pumped down had been turned into rock. The researchers just published these astounding findings in the journal Science.
This is amazing because it's not just Iceland that can do this. We could do this anywhere there's basalt.
Basalt is formed from volcanoes. Most of the sea floor is made of basalt and about 10% of continental rocks are too.
The Iceland scientists aren't being too hasty though. The next step is to try again at a larger scale.
The project is currently injecting 5,000 tons of carbon dioxide per year. They're planning to double that rate this summer and see how it works.
They're also being careful about any unintended consequences.
Some of the cores contained a greenish slime, for instance, which may be biological. Microbiologists are going to study this slime to learn how the Carbfix process might affect underground microbes.
And all of this research is key if we're going to stop climate change.
Carbon capture is a needed bridge to help us while we transition to clean energy.
In 2014, the International Panel on Climate Change included carbon capture in their list of options to help us limit climate change.
There's still a lot we need to do to stop climate change, but this technique could be a huge step forward.
There are many things we can personally do — such as limiting energy use and using our cars less — but we need action at the systematic level too.
"We need to deal with rising carbon emissions," said Dr. Jeurg Matter, lead author of the paper, in an article from Columbia University.
"This is the ultimate permanent storage — turning them back to stone."