Autunite, an ore of uranium, is found as a secondary mineral in oxidation zones of uranium deposits. As seen in the pictures above, the mineral is usually bright yellow to fluorescent green. The mineral's crystals are usually tabular, but can grow as scaly aggreagates. The crystals have a pearly to vitreous luster. It is strongly fluorescent under ultraviolet light and is radioactive:

Both images: http://mineral.galleries.com/

The mineral belongs to the tetragonal system with 4/m 2/m 2/m symmetry. It has perfect cleavage on {001} and poor cleavage on {100} (Nesse, 2000). Autunite is a uniaxial mineral with a negative optic sign. It has a hardness of 2-2.5.