But they're so green!
We recently needed some radioactive material for an experiment so what do you do? Jump on Ebay and United Nuclear of course!
Marbles on the envelope they arrived in
Known as green Vaseline glass, they used Uranium Oxide in the 50s and 60s to get the effect. As a (potentially bad) side effect, it’s 200 CPM! MightyOhm has a great writeup on various nuclear sources around your house.
In this age of crazy shipping restrictions we were blown away that (ok very slightly) radioactive marbles arrived in a first-class mail envelope. So good!