The second most rarest element in the world is francium. This extremely radioactive metal can’t be found in nature, although traces of it do occur in certain uranium minerals. No one’s ever managed to collect enough francium to be able to observe it in bulk, because it decays so quickly that any sample would instantly vaporize from the intense heat of its own decay. Francium is usually produced in laboratories by bombarding other elements with protons or neutrons to form a radioactive compound called actinium, from which francium can then be separated. This process is expensive and time-consuming, which makes francium one of the most costly of all naturally occurring substances.
Unlike most other metals, francium doesn’t have any stable isotopes. Most of it’s made up of the much more unstable actinium-K, which has a half-life of just 22 minutes. This makes francium even more radioactive than the element above it on the periodic table, astatine.
Francium’s incredibly short half-life also makes it dangerous to handle, as any atom of it would be instantly decomposed into other chemicals. This is why it’s used only in very tiny amounts, mostly for research purposes.
Its ability to bombard atoms and molecules with high-energy particles is one of its most useful qualities. This helps scientists to study their structures and properties. This is why francium is often used in atomic and nuclear physics, as well as in medicine.