Autunite (hydrated calcium uranyl phosphate) with formula: Ca(UO₂)₂(PO₄)₂·10-12H₂O is a yellow - greenish fluorescent mineral with a hardness of 2 - 2½. Autunite crystallizes in the orthorhombic system and often occurs as tabular square crystals. Due to the moderate uranium content of 48.27% it is radioactive and also used as uranium ore. If the mineral dries out, it converts 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. Museums are known to have covered the mineral with lacquer to avoid drying of the mineral.