Pollucite

Pollucite is a caesium-rich zeolite — a hydrated caesium-sodium aluminosilicate — and the single most important ore of the rare metal caesium. It interests collectors both for its rarity and for its role in producing caesium for atomic clocks, drilling fluids and specialty chemistry.

Identifying pollucite

Pollucite is hard (6.5–7) and usually colourless, white or grey, occurring as glassy massive material or rare cubic-looking crystals; it is easily mistaken for quartz or feldspar and often needs analysis to confirm. It forms in highly evolved, lithium- and caesium-rich granite pegmatites with minerals such as petalite, lepidolite and spodumene.

Where it is found

The world's great pollucite source is the Tanco pegmatite at Bernic Lake, Manitoba, Canada, which holds an enormous caesium reserve; it also occurs at Bikita in Zimbabwe and in pegmatites in Maine and on Elba, Italy.

For collectors

Because good crystals are rare, even massive pollucite from a classic pegmatite locality is collectable; provenance and association with other rare pegmatite minerals add interest.