But it was not to be. Estimates suggest that there is only about 30 g of francium in the whole of the Earth's crust. In the 1930s it was the turn of Fred Allison from the Alabama Polytechnic ...

As you can see the metal's get increasingly more reactive as you go down this group. We saw there lithium, then sodium and then potassium, but you didn't see rubidium, caesium and francium.