Mineral Resource of the Month: Cesium

by U.S. Geological Survey
Thursday, June 14, 2018

Marc A. Angulo, a mineral commodity specialist for the U.S. Geological Survey, compiled the following information on cesium, a metal used in atomic clocks, gas and oil drilling fluids, and medical applications.

Cesium, an alkali metal that is slightly golden in color and melts in one’s hand, is one of only two metals (along with mercury) that are liquid at room temperature. It is not found in nature in its elemental state because it is easily oxidized.

Cesium is found in low concentrations throughout Earth’s crust, but only the mineral pollucite has proven to be an economically feasible source of the metal. Pollucite, a cesium aluminum silicate, is found in lithium-bearing granites worldwide, with most of the world’s reserves located at Bernic Lake in Canada. Other pollucite deposits have been identified in Namibia and Zimbabwe, and cesium occurs in brines in Chile and China, but these have not been commercially exploited.

Because of its highly reactive nature, cesium has few uses, and even these require minute amounts of cesium; therefore, there is relatively little production and consumption of this metal. The most widespread use of cesium is in cesium formate brines, a high-density, low-viscosity fluid used for high-pressure/high-temperature oil and gas drilling. When drilling a borehole to extract oil and gas, cesium formate is poured down the inside of the drill shaft, where it exits through the drill bit. This maintains hydrostatic pressure in the well and protects drilling polymers from thermal degradation while cooling and cleaning the drill bit. About 85 percent of the cesium formate used can be retrieved and recycled for use in other drilling operations. The petroleum industry consumes more than half of the cesium produced annually.

Cesium is also used in atomic clocks and plays a vital role in GPS, the Internet, cell phone transmissions and aircraft guidance systems. The accuracy of GPS and aircraft guidance depends on the precision of timekeeping — position is calculated on the precise timing of signals sent to and received from stations or satellites, which use several cesium atomic clocks. Cesium clocks monitor the cycles of microwave radiation emitted by cesium’s electrons and use these cycles as a time reference.

Cesium-131 and cesium-137, the radioisotopes of cesium produced by the nuclear fission of uranium-235, are used primarily to treat cancer. Both have been used in brachytherapy, a treatment that implants a radioactive source, or seed, near a cancer site with the intent of destroying cancerous cells. With a shorter half-life and higher energy, cesium-131 is used as a safer, more effective alternative to iodine-125 and palladium-103 in the treatment of prostate cancer.

For more information on cesium and other mineral resources, visit minerals.usgs.gov/minerals.


Mine production, consumption, import and export data for cesium have not been available since the late 1980s, but world production is estimated to be more than 45,000 kilograms per year.

World consumption is estimated to be less than 50,000 kilograms per year, with nearly half consumed in the United States.

Canada is the leading producer and supplier of cesium ore, and the United States relies on Canada for all of its cesium.


Cesium was the first element discovered using spectroscopy, a technique devised by chemists Robert Bunsen and Gustav Kirchoff to analyze light generated when an element is heated. Each element radiates a unique set of bands of light when heated.

“Cesium” is derived from the Latin word “caesium,” meaning “bluish gray,” referring to the blue lines cesium generates under the spectroscope.

In its elemental state, cesium reacts explosively in water, forming cesium hydroxide.

The international definition of a second is based on the cesium atom. Cesium atomic clocks are highly accurate, gaining or losing only one second in 50 million years.

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