Pollucite is a
zeolite mineral with the formula (
Cs,
Na)
2Al2Si4O12·2
H2O 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.