There are only about 25 grams of francium in Earth's entire crust
An alkali metal so radioactive it destroys itself in minutes — at any instant, less than an ounce exists in the whole planet's crust.
Francium is the heaviest of the alkali metals and one of the rarest naturally occurring elements on Earth. According to Britannica, only about 24.5 grams — under an ounce — exist in the entire crust at any one moment.
The reason is its ferocious instability. Francium forms fleetingly during the radioactive decay of heavier elements, but its most stable isotope, francium-223, has a half-life of just 22 minutes before it decays away. As fast as nature makes it, it vanishes.
Natural francium cannot be isolated in visible, weighable amounts.
It was the last element to be discovered in nature rather than made in a lab, identified in 1939 by the French chemist Marguerite Perey, who named it after her homeland. Today scientists study it only as a handful of atoms at a time, trapped and chilled with lasers.
Sources & references
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