File:Muromontite.png

Summary
This is a sample of the naturally occurring mineral muromontite, which is a mixture of uranium and beryllium. The alpha particles from the decay of uranium are captured by the beryllium atoms, which in turn release neutrons. The neutrons are in turn re-captured by the uranium, which then undergoes further decay and is transformed into plutonium. The result is that this mineral contains the highest known naturally occurring concentration of plutonium.