Mineral Resource of the Month: Thorium

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

James B. Hedrick, a mineral commodity specialist for the U.S. Geological Survey, compiled the following information on thorium, an element that can fuel a nuclear reactor, produce light from a camping lantern or cook your dinner.

The original microwave, built in 1947 and called the Radarange®, was almost two meters tall and cost $5,000. Credit: Roy Stevens/Time Life Pictures/Getty Images

Thorium is a naturally occurring radioactive element usually found with other minerals, such as monazite in alkalic igneous deposits and carbonatites.

Thorium has a multitude of uses. It is used to generate power, produce light, transmit energy, resist ultra-high temperatures, impart strength to metals and control electrical currents. Most thorium consumed in the United States is used in catalyst applications, such as thorium-copper intermetallics to synthesize methanol from carbon monoxide and hydrogen, thorium sulfate to produce nitrogen-alkylated amines, and thorium oxide to convert ammonia to nitric acid. Thorium nitrate is used to produce thoriated tungsten welding electrodes, which are used to join stainless steels, nickel alloys and other alloys. Alloyed with magnesium, thorium imparts high-strength and creep resistance at high temperatures. This lightweight aerospace alloy has been used in jet engine housings and helicopter motor cowlings.

Thorium’s largest potential use is as a nuclear fuel. The Th232/U233 fuel cycle has many advantages over the currently used uranium fuel cycle. For one, the byproducts from nuclear fuel production from thorium can’t be used to make nuclear weapons. Moreover, thorium can incinerate weapons-grade plutonium in its fuel cycle, rendering the plutonium unusable as a nuclear weapon. Additionally, the volume of its byproduct waste from nuclear power generation is 1,000 to 10,000 times less than that of uranium, and it is about three times more abundant than uranium.

Visit minerals.usgs.gov/minerals for more information on thorium and other mineral resources.


Thorium is produced as a byproduct during the processing of the rare-earth thorium phosphate mineral monazite, itself a byproduct of processing heavy mineral sands for ilmenite, rutile, zircon, and to a lesser extent cassiterite.

The United States imported all of its thorium in 2008, yet the U.S. reserve base is about 20 percent of the world total.

The United States has large resources of thorium in monazite in placer deposits in the southeastern United States and in thorite primarily in vein deposits associated with alkalic igneous rocks and carbonatites in Colorado, Idaho, Montana and Wyoming. The United States last produced monazite in 1994 as a byproduct of heavy mineral sands processing in Florida.

India was the leading producer of byproduct thorium in 2008 and has one of the world’s largest stockpiles, which it plans to use to generate nuclear power.


Thorium is named for Thor, the ancient Norse god of thunder.

The element was discovered in 1828 by Swedish chemist and mineralogist Jöns Jakob Berzelius when it was isolated from a previously unknown black silicate mineral from the Island of Lövö near Brevig, Norway.

Thorium oxide emits an intensely bright white light when heated by a flame and has been used in camping lanterns, gas lamps and oil lamps for more than a hundred years.

Th232 emits low-energy radioactive alpha particles, which will not penetrate a piece of paper or your skin, but should be handled carefully and not inhaled or ingested.

In 1947, Raytheon commercialized this discovery and built the first microwave oven (thorium-containing magnetron tube) called the Radarange®. It was almost 1.8 meters tall, weighed 340 kilograms, and cost about $5,000.

A colloidal suspension of thorium dioxide particles was used in X-ray diagnostics as an intravascular contrast agent from the 1930s until 1955, but was abandoned when it was discovered to be carcinogenic. A similar product was prescribed as an orally administered contrast agent for imaging the gastrointestinal tract.

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