Autunite, is a hydrated calcium uranyl phosphate mineral - meaning water is part of the crystal structure.  

Due to moderate uranium content it is radioactive and also used as uranium ore. Autunite fluoresces bright green to lime green under UV light. The mineral is also called calco-uranite, but this name is rarely used and effectively outdated.

Autunite was discovered in 1852 near Autun, France, which is also autunite's namesake.  It occurs as an oxidation product of uranium minerals in granite pegmatites and hydrothermal deposits.  Associate minerals include metaautunite, torbernite, phosphuranylite, saleeite, uranophane and sabugalite.

If the mineral dries out, it can lose its water content and convert to meta-autunite-I, which can turn into meta-autunite-II after heating. These two subsequent minerals are very rare in nature. For scientific studies it is recommended to store the mineral in a sealed container to minimize the water loss.