Autunite specimens, which transform into meta-autunite by losing naturally water molecules, from this Portuguese mine are among the most aesthetically pleasing in the world due to their intense yellow-greenish colour, transparence, and luster. In this specimen we can observe numerous aggregates of tabular crystals, some isolated and contrasting on the stalactitic matrix. SEM-EDS analyzes have been carried out confirming the presence of Mg, but in a very small amount. Fluorescence under LW-UV light is exceptional.