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What are Radioactive Minerals? 6 Common Radioactive Rocks

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There is a good chance that you have collected a specimen with radioactivity while out rockhounding without even knowing it. While this may be interesting, is it also dangerous?

Almost all radioactive minerals on earth contain uranium or thorium in their chemical composition. These minerals are found in the same places you search for rocks and gems – pegmatites, granites, and gneisses. While they can emit different rays, most of their toxicity is caused by the radon they produce as they decay – determined by their half-life.

Now that you know that you are closer to radioactive minerals than you may have realized, what if I told you that the bananas you saw at the grocery store last weekend are also filled with radioactivity? Indeed, potassium is the slightest bit radioactive. So, does radioactivity really matter? Let me explain.

If you are interested in checking out the best safety gloves for rockhounding you can find them by clicking here (Amazon link).

6 Common Radioactive Rocks

What are Radioactive Minerals? Common Radioactive Rocks
What are Radioactive Minerals? Common Radioactive Rocks

Rockhounds come into contact with radioactive minerals all the time. Before I tell you what it really means for a mineral to be radioactive, and why it matters, here is a list of common radioactive minerals.

  1. Uraninite
  2. Thorianite
  3. Monazite
  4. Carnotite
  5. Brannerite
  6. Davidite

And now let’s take a closer look at these 6 most common radioactive minerals in the section below.

Uranite

Uranite is what is called a primary uranium ore mineral, which means that when uranium is mined, they usually look for uranite. If you have ever encountered a mine that had a caution – radioactive sign around it, chances are this mine holds traces of a primary uranium ore mineral (uranite is one of two).

If uranite was the main mineral from which the mine made its profit, then you probably would not be able to see this mine up close – it would be blocked off well before the entrance.

Uranite is just uranium oxide, though you may have heard of it under the name of pitchblende. Pitchblende is what large deposits of uranite are called.

Uranite looks like a black or grey quartz when there is enough of it to crystallize, but often it is just a highly metallic black or grey sheen in a rock full of different kinds of minerals.

Thorianite

This mineral is very similar to uranite if uranium was swapped out for thorium – the other common radioactive mineral – in that it is just thorium oxide.

It is less radioactive than Uranite in terms of how radioactive it is, but it is actually harder for scientists and miners to deal with because its rays are harder to shield (more on this in the coming sections).

Thorianite can also form dark crystals, but like uranite, it is usually present just in traces in rocks with other minerals. This mineral is found in sand and pegmatite, mostly in the south of Africa and Asia, but also has been reported in the black sands on riverbanks of the Missouri River, Scott River, and Nixon Fork in the USA.

Monazite

Monazite is a rare earth mineral that contains thorium. It is recognizable by its color similar to dark orange amber (if you want to test the difference, monazite will have a white streak – see our article on testing for more details on this!).

It is also found in sands but also found as a secondary mineral in gold, platinum, and magnetite deposits, as well as with several gemstones.

While Australia is the main producer of monazite, you can also find it in Brazil and Southeast Asia. While there are no mines in the USA, trace amounts have been found in the South Atlantic, just off the coast of Florida, and in Idaho as a sand deposit.

Carnotite

Carnotite is a secondary uranium mineral but also is a rather important source of radioactive material. It contains uranium, vanadium, and potassium, one of the least radioactive (but still radioactive) minerals.

If you’ve been rockhounding in Colorado or throughout the west of the United States and come across a radioactive sign on a closed mine, this is most likely the mineral which was mined there (closed a few decades after World War II most likely, as most were). This mineral can be found in weathered sandstone in conjunction with calcium-based minerals.

Brannerite

This mineral is mainly found in areas with gold, the most noticeable usually being as crystal form in the quartz, famously also found in areas with gold.

It contains uranium and is also found in the West US, primarily Wyoming and Idaho. One interesting thing about this mineral is that it’s one of the most common radioactive materials in Europe, commonly found in the Alps and Pyrenees (together with davidite).

In crystal form, brannerite will be black to grey or brown. It will mainly form as crystals and is sometimes even mistaken for tourmaline. You may want to perform a test for radioactivity if you stumble upon black crystal amid quartz in an area known to have gold.

Davidite

Davidite is the last commonly found radioactive mineral discussed in this article, and is the second primary Uranium ore, next to uranite. It is found in pegmatites, also mostly in Europe, the Middle East, and Russia.

You may encounter davidite as granular, dark-colored metallic crystals in rock containing mainly nonmetallic minerals.

BTW: Do you want to know more about rocks and minerals identification? The books listed below are the best ones you can find on the internet (Amazon links):

What Does it Mean for a Mineral to be Radioactive?

Radioactive, by definition, means that this mineral will tend to extinction, breaking down into other substances.

The time taken for this mineral to disappear is given by its half-life or decay rate. A half-life is a time taken for one-half of a mineral to break down. The nature of a half-life is that at first, radioactive material will decay quickly, but after time, the rate will slow down until only tiny amounts persist, but persist forever.

Radioactive materials are rated based on this tendency towards extinction, along with other things. Minerals that decay faster are said to be more radioactive.

Because of this tendency of radioactive minerals to disappear, some of them are so rare that crystals cannot even be formed with them anymore. This means that the more common the naturally radioactive material, the less radioactive it likely is.

A good comparison is with uranium, tritium, and Technetium-99. Uranium takes a very long time to decay so that even though it is found naturally, it is still rather common in terms of radioactive elements.

Tritium, on the other hand, is comparatively very radioactive and is therefore extremely rare. Technetium-99 is a man-made material used in medicine, with a half-life of 6 hours. This is a dangerous mineral, far more dangerous than naturally occurring radioactive substances.

UraniumTritiumTechnetium-99
Half-life4,500,000,000 years12.3 years6 hours
Natural or manmade?NaturalNaturalManmade
Is it common?YesNo
Is it dangerous?IndirectlyYesExtremely
Level of Radioactivity Comparison (source)

TIP: Are you interested in finding radioactive rocks? First of all, you need to be careful and use tools like Geiger Counter that can help you to find radiation. Find out more about rockhounding with Geiger Counter in the article below:


How to Pick and Use a Geiger Counter for Rockhounding


What are Radioactive Decay Rates in Minerals Affected By?

Radioactive decay rates depend on the mineral and are mostly dependent on where in the chain of decay the element finds itself in. To look at the chain of decay, we must look more closely at the life of radioactive substances.

Uranium is thought to be generated in supernovas or on neutron stars and then enriched in the Earth’s crust. It has an extremely long half-life seen above.

It decays into a certain isotope of thorium briefly (half-life of 24 days), which in turn decays back into a different uranium isotope through an element called protactinium (half-life of 1 minute). This isotope of uranium decays into the more stable version of thorium (a half-life of 75,000 years).

After a while, this thorium decays into radium (half-life of 1602 years), which decays into the radioactive gas Radon. Radon has a half-life of 4 days.

After radon, there is a complex decay chain that ends up settling into some of the poisonous minerals we know today which are not radioactive, meaning they do not decay but are still harmful. These minerals contain lead, thallium, and mercury.

ElementDecay Chain
U-2384,500,000,000 years
Th-23424 days
Protactinium1 minute
U-234245,500 years
Th-23075,000 years
Radium1602 years
Radon4 days
Uranium Decay Chain

In the example of the uranium decay chain, it can be seen that the half-life (generally) decreases as the substance decays into lower-tier substances.

TIP: Radioactive minerals can be characterized as cool rocks. Do you what are cool rocks and where to find them? Check out the article below and find out more:


What are Cool Rocks & Where to Find Them? Follow These Tips


Are Radioactive Minerals Dangerous?

Radioactive materials can emit 3 different types of waves: alpha, beta, and gamma. Alpha waves are positively charged and large, so they can be blocked by a mere sheet of paper. Beta waves are electrons, so much smaller and can penetrate 3mm into aluminum. Gamma waves are powerful photons and can even penetrate lead.

As long as the penetrations are mitigated through barriers, these waves are harmless. The main consideration is to not leave traces near your body, so rockhounding gloves and handwashing are good enough protection for a rockhound.

Radon is the most common harmful radioactive material because it is generated near any radioactive specimen. It is dense and will sink to the bottom of a container holding air, and it is very harmful to breathe.

It breaks down into stable dust particles of harmful material. Therefore, in mineral collections that store radioactive minerals, there may be harmful particles settling on the ground.

Be careful to wipe the dust away and not to breathe these particles in. Use mineral identification to see if a suspicious mineral is really radioactive.

When identification is uncertain, there are several tests that involve bringing the mineral near film in a dark space, then developing the film and looking for cloudy spots.

Conclusion

To wrap it up, be careful with your rock collections. Make a practice out of identifying your minerals and keep any questionable ones in an enclosed space to be extra safe.

Wear gloves while rockhounding, especially with metallic-looking materials. However, these minerals are not so dangerous to not be curious about, so if you are curious, you could go collecting them with the right precautions!

TIP: Stay safe when you go rockhounding and yourself. If you are interested in the best gloves for rockhounding, check out my top 3 picks in the article below:


3 Best Gloves for Rockhounding: Protect Your Hands