Good question. Most granite has a tiny amount of radium, which emit radon, a gas have that has shown to cause lung cancer when present in high amounts, but not enough to cause harm. Some granite slabs contain high concentrations of radium and our suppliers have identified regions where these come from, so they avoid those areas. Our slabs undergo radon testing, and each one we sell is guaranteed to pass EPA inspection against radon exposure. However, we make no guarantees about the ground over which your house is built, which has been identified as the most common source of radon gas.