Autunite (hydrated calcium uranyl phosphate), with formula Ca(UO<sub>2</sub>)<sub>2</sub>(PO<sub>4</sub>)<sub>2</sub>·10–12H<sub>2</sub>O, is a yellow-greenish fluorescent phosphate mineral with a hardness of 2–. 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 The mineral is also called calco-uranite, but this name is rarely used and effectively outdated.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, 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.
90,000 lbs of U<sub>3</sub>O<sub>8</sub> were produced from nine properties, although most of the ore came from the Daybreak Mine.
Other locations
One of the other locations of autunite includes Autun, France, the type locality and namesake of the mineral. The mineral was formed there as an alteration of uraninite and other uranium bearing minerals. Autunite is also found in Cornwall, Saxony, and North and South Dakota.