a chemical element with symbol Fr and atomic number 87. It was formerly known as eka-caesium and actinium K.[note 1] It is one of the two least electronegative elements, the other being caesium. Francium is a highly radioactive metal that decays into astatine, radium, and radon. As an alkali metal, it has one valence electron.

Uranium and thorium minerals produce francium in vanishingly small quantities via their natural radioisotope decay chains. At most a few atoms at a time exist in a rock like this, and you can't see any of them.