You're completely right and I just found that granite is radioactive. Like many other natural materials, it contains trace amounts of uranium. Some granite bodies, however, can have 5 to 20 times the normal amount of uranium, the byproduct of which is radon gas, which has been shown to cause lung cancer. But don’t worry about significant exposure to radiation from cragging in Joshua Tree Park or upgrading your kitchen with lavish stone counters. The biggest concern lies in poorly ventilated basements that are surrounded by soils coming from granite bedrock.