Uranopilite is a minor ore of uranium with the chemistry (UO<sub>2</sub>)<sub>6</sub>SO<sub>4</sub>(OH)<sub>6</sub>O<sub>2</sub>÷14H<sub>2</sub>O or, hydrated uranyl sulfate hydroxide.
As with many uranyl minerals, it is fluorescent and radioactive. It is straw yellow in normal light. Uranopilite fluoresces a bright green under ultraviolet light. Uranopilite contains clusters of six uranyl pentagonal bipyramids that share equatorial edges and vertices, with the clusters cross-linked to form chains by sharing vertices with sulfate tetrahedra. In uranopilite, the chains are linked directly by hydrogen bonds, as well as to interstitial H<sub>2</sub>O groups.
Uranopilite is associated with other uranyl minerals such as zippeite and johannite and, like them, is usually found as an efflorescent crust in uranium mines.
Notable occurrences include: