Well, it’s not all that easy to tell. There may be trace amounts of radon emitted from your granite countertops, but it’s unusual that those are high enough to pose a serious health risk. Radon is a naturally occurring substance that is odorless and colorless. It is caused by the breakdown of naturally occurring radioactive elements (e.g. thorium, uranium) over time as they decay. These elements are found in rock and soil all around us. There isn’t much of a health risk in small doses, but in larger concentrations, they significantly increase the likelihood of lung cancer.
Granite is formed from igneous rock cooling in the earth; then, it gets mined, processed, and shipped to your home. So there is some chance of the rock having more or less of these radioactive elements, but typically there will already be a significant decay as the slabs move away from their source.
The much greater risk to your health is not the countertops but the soil around your home’s foundation. Estimates say that 1 in 15 homes may need radon ventilation installed to prevent health dangers from long-term exposure. They sell test kits for it, or the more sure method is to bring in a specialist to test your home.