Autunite (hydrated calcium uranyl phosphate), with formula Ca(UO2)2(PO4)2·10–12H2O, is a yellow-greenish fluorescent phosphate with a hardness Autunite crystallizes in the orthorhombic system and often occurs as tabular square crystals , commonly in small crusts or in fan-like masses. Due to the moderate uranium content of 48.27% 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 The mineral is also called calco-uranite, but this name is rarely used and effectively outdated.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 , which is also autunite's namesake. It occurs as an oxidation product of uranium minerals in granite and hydrothermal deposits. Associate minerals include metaautunite , phosphuranylite and sabugalite