I'm sure you could probably find some granite rocks that were 'hotter' than others. Granites with mineable amounts of Uranium are found in many locations both in the USA, Canada, and elsewhere around the world. NH, my current home state, is known as the Granite state, and many areas DO have natural radon problems. A lot of granite from this area is used to build buildings, curbs, steps, etc. Living above about 4,000 feet gets you zapped by much more ionizing radiation than you'd likely get from any decorative stone you may have in your house. In fact, flying cross-country is pretty high in irradiation - easily the equivalent to a chest x-ray.
