IGC Pollucite Colorless pollucites lack fire when cut and are usually small. However, this very rare cesium mineral is a coveted collector’s gem. Not only is gem-quality pollucite very rare, but it’s also the only mineral which has cesium (Cs) as an essential constituent. This mineral serves as the principal ore for cesium. Pollucite belongs to the zeolite mineral group. It forms a solid solution series, as the cesium analog, with analcime, the sodium analog.