OK, it’s a specific kind of rock:
CleanTechnica.com:
Scientists at Columbia University have discovered that a rock found in the Middle East can be used to soak up carbon dioxide at a rate high enough to significantly slow global warming.The team found that when the rock, known as Peridotite, comes into contact with carbon dioxide it converts the gas into harmless minerals such as calcite. They have also worked out a way to ’supercharge’ the naturally occurring process to a million times its normal speed to grow enough of the mineral to permanently store 2 billion or more tons of carbon dioxide annually. This equates to an astonishing 7 per cent of the total global carbon emissions from human activity each year.
Found [via].