In 1828, Norwegian mineralogist Morten Thrane Esmark sent for analysis to Swedish chemist Jöns Jacob Berzelius an unknown mineral, in which was identified a new, silvery-white, actinide element that Berzelius named Thorium (atomic number 90 and symbol Th on the periodic table), after the Norse god of thunder. Interestingly, the first observations of thorium’s radioactivity in 1898 came from two independent sources – Gerhard Carl Schmidt and Marie Curie. And, it was Ernest Rutherford and Frederick Soddy’s work from 1900 to 1903 with thorium decay that led to the scientific concept of the “half-life”, or the time it takes for the radioactivity of a specific isotope to fall to half its original value.

Long before scientists understood radioactivity, though, thorium was lighting up the world in street lamps and camping lanterns.

Amazing Facts About Thorium

What else should you know about thorium? Read on to learn more about this remarkable energy metal!

1. Thorium has a high melting point (1750°C) – higher than most common metals and many specialized metals and alloys (for example: uranium melts at 1132°C, the various steels melt at from 1371°C to 1540°C, iron melts at 1538°C, palladium melts at 1555°C, and titanium melts at 1668°C.
2. Thorium occurs naturally in soil at an average concentration of about 6 parts per million, making it roughly as common as lead and approximately three to four times more abundant in Earth’s crust than uranium.
3. Thorium rarely travels alone through geological processes – it forms an intimate association with rare earth elements in mineral deposits worldwide. For example, India’s roughly 25% possession of the world’s thorium reserves are primarily in monazite beach sands.
4. The world’s largest thorium deposit sits in Chile’s Puna de Atacama region in the Atacama Desert, though it remains largely unexploited. 
5. While highly dispersed at about 0.05 parts per billion, the world’s oceans hold vast quantities of thorium (approximately 100,000 tons of dissolved thorium) that continuously wash in from continental erosion. Extracting it remains economically impractical, but represents a theoretically inexhaustible resource.
6. The thorium in a single ton of monazite sand contains the energy equivalent of approximately 20 tons of coal or 8 tons of oil.
7. Some of Earth’s geothermal energy comes from the radioactive decay of thorium deep within the planet’s crust, contributing to geological processes that shape our planet’s surface and maintain its magnetic field.
8. Thorium-232 has a half-life of 14.0-14.05 billion years, approximately the age of the universe. As a result, thorium isotopes serve as “cosmic chronometers”, with thorium-232 a primordial nuclide that provides scientists with key information for dating the creation of our solar system and understanding stellar nucleosynthesis processes. For example, marine sediments containing thorium isotopes have revealed climate patterns spanning ice ages, while meteorites rich in thorium provide timestamps from the solar nebula’s collapse 4.6 billion years ago.
9. Thorium’s atomic structure exhibits crystalline polymorphism, with different crystal structures forming under different temperature and pressure conditions: face-centered cubic at room temperature, body-centered cubic at elevated temperatures, and exotic high-pressure phases. Each crystalline form preserves information about the environmental conditions during its formation, making thorium samples natural archives of physical forces over geological time scales.
10. Thorium exhibits remarkable solubility and chemical compatibility with liquid metals, particularly lead and bismuth, creating opportunities for revolutionary reactor coolant systems.
11. Thorium requires a “starter” fissile material (like uranium-235 or plutonium-239) to begin the breeding process to uranium-233.
12. Unlike uranium, natural thorium cannot be used directly as nuclear fuel without first being converted to uranium-233 through neutron bombardment.
13. When thorium-232 absorbs a neutron, it becomes thorium-233, which then undergoes two beta decays to become uranium-233 over approximately 27 days.
14. The uranium-232 contamination in thorium-bred uranium-233 makes it extremely dangerous to handle and difficult to weaponize, providing inherent proliferation resistance.
15. The thorium-230/uranium-234 decay chain creates an atomic clock that ticks with extraordinary precision over hundreds of thousands of years.
16. Unlike plutonium or enriched uranium, metallic thorium emits primarily alpha particles that cannot penetrate skin. While you shouldn’t make a habit of it, briefly handling thorium metal poses minimal radiation risk (though thorium dust should never be inhaled due to its chemical toxicity and long-term radiation exposure).
17. The thorium-229 nucleus possesses an excited state approximately 8.35-8.4 electron volts above its ground state – an energy so remarkably low that it falls within the range of ultraviolet lasers rather than the gamma rays typically associated with nuclear transitions. When thorium-229 nuclei are embedded in transparent crystals and subjected to precisely tuned laser light, they create what physicists call a “nuclear laser” or “graser” (gamma-ray laser).
18. In powdered form, thorium is so reactive with oxygen that it can burst into flames when exposed to air at room temperature, producing brilliant white sparks. This makes thorium metal difficult to machine and store, requiring inert atmosphere handling similar to lithium.
19. In the 1940s-1950s, German company Auergesellschaft marketed a radioactive toothpaste called “Doramad” that contained thorium, claiming it would make teeth shine and provide antibacterial benefits. Of course, it was eventually banned.
20. High-quality camera lenses and precision optics in the early-to-mid 20th century often contained thorium oxide to improve light-bending properties. Some vintage camera lenses from this era can still trigger radiation detectors.

Final Thoughts

Whether thorium will transform from a scientific curiosity into a cornerstone of future energy systems remains an open question, but one thing is certain: this remarkable element continues to surprise us with applications ranging from the exotic physics of nuclear lasers to the mundane reality of vintage camera lenses quietly ticking away in collectors’ cabinets. 

In thorium, we find not just an element, but a testament to the hidden complexity and potential that lies within the periodic table.

Thanks for reading!