Cesium

Overview

Cesium (spelled caesium in British English) is a soft, gold-colored alkali metal. It melts at 28.5 °C, is quickly attacked by air and reacts explosively with water.¹ Most applications use only a few grams of cesium. Its importance comes from a few hard-to-replace uses: high-density drilling fluids, industrial catalysts and atomic clocks.²

Cesium is on the US Final 2025 List of Critical Minerals.³ It is not on the EU's critical raw materials list.⁴ The United States has been entirely dependent on imports of cesium minerals, and global supply is small and poorly documented.²

Where it comes from

The main cesium ore mineral is pollucite. It is found mainly in zoned granite pegmatites rich in lithium and containing lepidolite or petalite, and typically contains 5% to 32% cesium oxide. Lower concentrations occur in brines in Chile and China and in geothermal systems in China, Germany and India. Cesium-bearing clays have been identified in Laos, where in situ extraction is being researched.²

There are no official production data for cesium, so no production chart is shown. The main global producers are thought to include Canada, China, Germany and Russia. In 2025 the Tanco Mine in Canada reported intermittent cesium production and processing from ore and stockpiles. Recovery of cesium from tailings at the Bikita Mine in Zimbabwe, for shipment to China, restarted in recent years.²

USGS cannot assign reserves to individual countries. It estimates that Australia, Canada, China and Namibia together hold less than 200,000 t (as cesium oxide). Several projects that could produce cesium as a by-product of lithium or rubidium mining were at the exploration or feasibility stage in 2025, in Canada, Laos, Namibia and the United States. One Namibian lepidolite project had a measured and indicated resource of about 3,100 t of cesium. It went into independent administration at the end of 2024 for lack of financing.²

What it is used for

By quantity, cesium carbonate and cesium hydroxide are the leading cesium products, followed by cesium formate, iodide, nitrate and chloride.²

• Catalysts. Cesium catalysts have largely replaced potassium promoters in high-purity sulfuric acid production. They are also the main catalysts for making methyl methacrylate without the conventional cyanide-based process.²
• Drilling fluids. Cesium formate brines are used to drill high-pressure, high-temperature oil and gas wells. About 11,000 t of cesium formate is in use, and about 5% of it is lost and replaced each year.²
• Imaging. Cesium iodide is used mainly in X-ray panels and as the input phosphor of X-ray image intensifiers.²
• Timekeeping. Cesium is the atomic frequency standard in atomic clocks. These clocks are vital for aircraft guidance, GPS satellites and internet and mobile-phone networks.²
• Isotopes. Cesium-131 is used to treat some cancers. Cesium-137 is used in industrial gauges, mining and geophysical instruments, and to sterilize food, sewage and surgical equipment.²

Because cesium-137 is radioactive and dangerous, Congress has set the National Nuclear Security Administration a goal of eliminating cesium-137 blood irradiators in the United States by 2027.² Cesium is also used in special optical glass, vacuum tubes and radiation monitoring equipment.¹

Grades and forms

Cesium is sold mainly as chemicals rather than metal. Cesium metal is not traded in commercial quantities.²

Trade and policy

The United States has had no consumption, import or export data for cesium since the late 1980s. It is estimated to use no more than a few thousand kilograms of cesium chemicals a year. Before 2016, Canada was believed to be the main supplier of ore and refined chemicals to the United States. Recent import data suggest that China and Germany now supply cesium chemicals. US tariffs on cesium compounds are classified under general "other" lines for alkali metals and their salts. There is no government stockpile.²

Recycling and substitution

Cesium formate brines are usually rented to oil and gas operators. After a well is finished, the brine is returned and reprocessed, and nearly 85% of it is recovered. Cesium iodide is recycled from radiography panels into new panels, which is believed to be standard practice in the industry.²

Cesium and rubidium can often be used interchangeably because their physical properties and atomic radii are similar. Cesium is more electropositive, which makes it the preferred choice in some uses. Rubidium is no easier to obtain, because it comes from the same deposits in smaller quantities.²

Sources

1. Caesium: element information, properties and uses. Royal Society of Chemistry, accessed 2026-10-03. ↩ ↩²

2. Mineral Commodity Summaries 2026: Cesium. U.S. Geological Survey, accessed 2026-10-03. ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹² ↩¹³ ↩¹⁴ ↩¹⁵ ↩¹⁶

3. Final 2025 List of Critical Minerals. Federal Register, accessed 2026-10-03. ↩

4. EU critical raw materials. European Commission, Joint Research Centre (RMIS), accessed 2026-10-03. ↩