Radon is a naturally-occurring radioactive gas found in soil and rock, including granite. As trace uranium in soil and rock decays, it emits radon, which is a leading cause of lung cancer. To accurately determine the radon content of a granite countertop, you will need to compare the radon level of the granite sample to the natural radon level of your home. The Environmental Protection Agency displays a list of places to purchase radon test kits for your granite counter, or you can call your state's Radon Officer for detailed information.
Request a sample of granite from the stone dealer or mason. Make sure your sample is from the same slab of granite as the one you intend to buy.
Purchase a radon test kit from Radon.com (see Resources) or another supplier. Place the granite sample on a countertop in your kitchen.
Read the manufacturer's instructions for using the radon kit. Excessive heat or humidity may affect the test results.
Set one radon tester in your basement.
Place a second radon tester next to the slab of granite. Radon.com says not to cover the sample and the radon kit with a large bowl or other object, since this can artificially inflate radon readings.
Do not disturb the radon test kits until the test is concluded. Your test kit will tell you how long to leave the radon detectors.
Locate the radon reading on both testers, which is given in pCi/L or picocuries per liter of air. Examine the basement reading first. A reading below 2 pCi/L in your basement is standard. If you encounter a reading of 2 to 4 pCi/L in your basement, hire a professional radon tester to do a lengthier follow-up exam. A reading above 4 pCi/L in your basement means you have a radon problem in your house.
Compare the granite reading to the basement reading. If the granite reading is higher than the basement reading, the granite is potentially hazardous. If the readings are similar and are both below 2 pCi/L, you may purchase the granite without worry.