The Autunite/Torbornite Group includes some rare radioactive minerals, some of which are popular among collectors. Also called the "Uranium Mica Group", the group is similar to micas in its layered structure. The layering produces a perfect cleavage that yields sheets. Unlike the micas, members of this group are tetragonal and their crystals tend to be square tabular to pseudocubic.
The general formula of this group is M(UO2)2(XO4)2-8 to 12H2O. The M ion can be either calcium, copper, barium, iron, magnesium and manganese. The X ion can either be phosphorous, arsenic or vanadium. The structure is composed of XO4 tetrahedrons linked to uranium-oxygen groups that form distorted octahedrons. The XO4 and uranium groups lie in sheets that are weakly held together by the water molecules.
Many members of this group can lose water molecules or dehydrate to a different mineral that belongs to the meta-autunite/meta-torbernite group of minerals.
These minerals are some of the more common minerals of the Autunite/Torbernite Group: