Pollucite is a zeolite mineral with the formula (Cs,Na)2Al2Si4O12·2H2O with iron, calcium, rubidium and potassium as common substituting elements.

It has a Mohs hardness of 6.5 and a specific gravity of 2.9, with a brittle fracture and no cleavage.

It is named for Pollux, the twin of Castor on the grounds that it is often found associated with petalite (previously known as castorite).

[9] 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.

About 82% of the world's known reserves of pollucite occur near Bernic Lake in Manitoba, Canada, where they are mined for their caesium content for use in caesium formate oil drilling assistance.