Calcite
Complex shape X, 1cm long; it is a 2nd generation formation, grown (together other XX, as you can see in the other photo below) on white brilliant 1st generation scalenohedron of the same mineral. This Pb/Zn mine (some time known as Pubusinu mine) is south of Fluminimaggiore, near Su Zurfuru mine, along the way to Arenas
11.5x7cm
Gutturu Pala mine (Pubusinu), Fluminimaggiore, Carbonia-Iglesias. Italy
Specimen n.598

Another photo: entire specimen