Pollucite is a zeolite mineral with the formula (Cs,Na)2Al2Si4O12·2H2O with iron, calcium, rubidium and potassium as common substituting elements. It is important as a significant ore of caesium and sometimes rubidium. It forms a solid solution series with analcime. It crystallizes in the isometric - hexoctahedral crystal system as colorless, white, gray, or rarely pink and blue masses. Well formed crystals are rare. It has a Mohs hardness of 6.5 and a specific gravity of 2.9. It has a brittle fracture and no cleavage.
Its typical occurrence is in lithium-rich granite pegmatites in association with quartz, spodumene, petalite, amblygonite, lepidolite, elbaite, cassiterite, columbite, apatite, eucryptite, muscovite, albite and microcline.
It was first described in 1846 for occurrences on Elba Island, Italy, it is named for Pollux (mythology), the twin of Castor on the grounds that it is often found associated with petalite (previously known as castorite).
Francium occurs in trace quantities in certain pollucite ores, and some of the initial and much-disputed discoveries involved the spectral analysis of pollucite, showing unexplained lines that could only be explained by the existence of a new element.(from Wikipedia)
The stone cames from Pakistan and it has some small inclusions. Cut by Luigi Mariani.