Research into granite counter tops and radiation

Research into the implications of granite counter top construction and use has found that workers fabricating granite are exposed to significant radiation doses. Granite is a term for natural stones such as pegmatites, migmatites, gneisses, and schists used for residential countertops and other indoor trim. About 5% of granite sold in the US has elevated concentrations (several times natural background) of naturally occurring radioactive materials, containing uranium and thorium.