The fad for granite kitchen countertops looks like it may last a couple of million years, the radiation that is, not the fad. According to Rice University physics professor, W.J. Llope, some granite countertops have enough uranium to pose a danger to humans. Some of the countertops produce both radon and radiation. Radon is the number two cause of lung cancer just behind smoking.
Some granite countertops emit radiation at levels much higher than typical atmosphere exposure. Some samples have levels 25 times higher than recommended EPA levels. Not much testing has been done on kitchen radiation and radon levels but it appears most countertops are in the safe range according to the Marble Institute of America. None the less, if it were my home I would go for the testing.
The American Association of Radon Scientists and Technologist have a web site that can help you find someone local and qualified to test your counters. The cost can run several hundred dollars. Also, if you Google “radon test kits” you can find them for under $12.00 at Amazon but they will not test for radiation. I would recommend the professional over the self-test kits.
Most of Marin County real estate does not have an issue with radon from the ground so not many properties here have been tested but it looks like this might be a newly popular test, for the kitchen anyway.