Radon is a hard element to pin down: You can't see it because it's a clear gas, and you can't even have a vial of it because it's extremely radioactive and has a half life of only 3.2 days. One place it can be found, if only in microscopic and invisible quantities, is in granite rocks. Granite contains uranium and thorium impurities, which constantly give off small amounts of radon gas. This is why areas of the country with certain kinds of bedrock also have problems with radon collecting in basements. And it's why large granite buildings are measurably more radioactive than normal.
I chose this sample to represent its element in my Photographic Periodic Table Poster. The sample photograph includes text exactly as it appears in the poster, which you are encouraged to buy a copy of.
Source: Kinetic Fountains
Contributor: Theodore Gray
Acquired: 10 August, 2005
Text Updated: 4 May, 2007