“NORMs” may be the Norm in Granite and Marble
NORM is an acronym for Naturally Occurring Radioactive Materials and because marble and granite are natural stones, small, measurable amounts of radiation or radon can be found in these materials.
Is this something to be concerned about? Generally no, however, these trace amounts can contribute to unsafe levels of radon if present elsewhere.
To see how randon in marble and granite countertops is calculated and measured, download this FREE pdf put together by Environmental Health and Engineering.