Page Image Page Content Radon gas is a naturally occurring radioactive gas that is invisible and odorless. It forms from the radioactive decay of small amounts of uranium and thorium naturally present in rocks and soils so some radon exists in all rocks and soils.adon-In its natural state radon is an odorless, colorless, tasteless, radioactive gas. It is the only naturally radioactive gas and is the heaviest of all of the elements that occur as gasses at room temperature and pressure conditions.