Francium is yet another element for which the only possible way to represent it is to post a picture of a uranium-bearing mineral. In this case, I chose a micromount box containing a small crystal of autunite (Ca(UO₂)₂(PO₄)₂·10-12H₂O).

A small micromount sample of autunite (hydrated calcium uranyl phosphate), illuminated by both visible and ultraviolet light.

This autunite sample is from the Daybreak Mine in Spokane, Washington. This mine is famous for producing some of the world’s best samples of autunite.

Like many uranium minerals, autunite fluoresces green under ultraviolet light. The uranium in this crystal, like all uranium, undergoes radioactive decay, changing into one element after another as the decay chain inexorably heads towards one of the stable isotopes of lead. Because francium lies on some of these decay chains, it is possible that, once in a blue moon, this crystal contains some francium. However, it is estimated that there is one francium atom for every quintillion (1,000,000,000,000,000,000) uranium atoms in any given sample, so it is highly unlikely that even a single atom of francium was present when I snapped these photos.