Caesium

A soft alkali metal used by the gram in drilling brines, catalysts and atomic clocks, mined from a handful of pegmatites.

Tech & minor metals · No. 51

• US critical 2025

Cesium defines the second in atomic clocks, and its dense brines are rented to oil drillers and mostly returned for reuse.

Chart: Illustration: Caesium

Where it comes from

Chart: Map of where it comes from

The main ore is pollucite, holding 5% to 32% cesium oxide, from lithium-rich pegmatites. Mining is almost a single-site affair, with much drawn from old stockpiles and tailings.

Three things to know

1. About 11,000 t of cesium formate brine is in drilling use, and only 5% is depleted and replaced each year.
2. Cesium is the most electropositive stable metal: it melts just above room temperature and reacts violently with air and water.
3. Congress set a goal to eliminate cesium-137 blood irradiators in the United States by 2027.

The journey

1. 1 PegmatiteZoned granite with lithium minerals
2. 2 PolluciteOre with 5-32% cesium oxide
3. 3 DigestionBroken down to sulfate or carbonate
4. 4 SaltsFormate, hydroxide, iodide and others
5. 5 End usesDrilling brines, catalysts, detector panels, clocks

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