This is an extension of a presentation I gave to the Ozark Mountain Gem & Mineral Society on 25 April 2022. Please click on the images to view copyright information.

10 Most Deadly Minerals

There are dozens of “# (pick a number) Most (insert favorite doom and gloom word here) Mineral” lists available on the internet. Nearly all of them have some combination of the following minerals listed:

I’m going to attempt to clear up some of the misconceptions in these types of articles from the authors making incorrect assumptions about toxic elements. I’ll do this by giving an in-depth introduction to how toxicity works and which types of minerals are a risk to mineral enthusiasts.

What is Toxicity?

Merriam-Webster defines toxicity as “an extremely harsh, malicious, or harmful quality.” Many of the same elements in minerals are ones our bodies need to work properly, but in large quantities can be damaging. Others have negative effects no matter how small the dose. A significant number of both of these types of elements are considered heavy metals, which just means they have a higher density and atomic weight than other elements.

Heat map of heavy metals in the periodic table

This table shows the number of heavy metal criteria met by each metal, out of the ten criteria listed in this section i.e. two based on density, three on atomic weight, two on atomic number, and three on chemical behaviour. It illustrates the lack of agreement surrounding the concept, with the possible exception of mercury, lead and bismuth. Six elements near the end of periods (rows) 4 to 7 sometimes considered metalloids are treated here as metals: they are germanium (Ge), arsenic (As), selenium (Se), antimony (Sb), tellurium (Te), and astatine (At).[16][n 2] Oganesson (Og) is treated as a nonmetal. Metals enclosed by a dashed line have (or, for At and Fm–Ts, are predicted to have) densities of more than 5 g/cm3.

How Does Toxicity Work?

There are a couple of ways that toxic minerals interact with the body to produce negative effects:

Lose one or more electrons, forming a metal cation, binding to macromolecules, and disrupting the important biological process resulting in:
- Gastrointestinal or kidney disfunction
- Nervous system disorders
- Skin lesions
- Vascular damage
- Immune system dysfunction
- Birth defects
- Cancer
Generate reactive oxygen species, disrupting DNA synthesis and repair
- Neuropsychiatric disorders
- Enzyme inactivation
- Suppression of antioxidant defense

Basic Notions of Toxicology

Dose

Nearly everything is harmful in big enough doses, but how often and how long you are exposed along with how you are exposed make a significant difference in how toxic it will be to you.

Bioavailability

Bioavailability is one of the most important notions in mineral toxicity. It refers to how much of the toxic element reaches the circulatory system. While there are a number of elements that have been found in their native state, only gold, silver, copper, and the platinum group (platinum, iridium, osmium, palladium, rhodium, ruthenium) can be found in large amounts. Normally elements bind to another element within the mineral, changing its properties.

For instance, sodium (Na) is a highly volatile metal. When water contacts it, it explodes by spontaneously producing hydrogen (H) and sodium hydroxide (NaOH). NaOH is highly caustic and will cause severe burns even though the explosion causes a relatively minor fire. Because sodium is so volatile, it’s never found naturally in its native state. It always forms compounds with other elements.

Sodium (Na)

Chlorine (Cl) is an extremely reactive gas and a strong oxidizing agent. It is poisonous to most living organisms and was used for chemical warfare during World War I. Because of its extreme reactivity, there are no natural sources of native chlorine. It also always forms compounds with other elements.

Chlorine (Na)

Sodium chloride (NaCl) is the most common compound of either chlorine or sodium. It is the 21st most abundant chemical in Earth’s crust and third most abundant in seawater. Sodium chloride is an essential component to life for its use in nerve impulse generation and electrolyte and fluid balance.

Sodium chloride is commonly called “salt.” While too much salt in your diet is harmful, you can’t live without it. So even though a mineral might contain a harmful element, more than likely that element is part of a compound that is not dangerous.

Sodium Chloride (NaCl)

For a mineral to be bioavailable, there are two things that must be true.

It is water- or acid-soluble (or both)
It can be broken down before it leaves your body

Water/acid-soluble minerals chemically react with the water and/or acids in your body, breaking compounds’ elemental bonds and forcing the elements apart or forming one or more new compounds. These elements/compounds now have access to the circulatory system. Some of these elements/compounds can bind to enzymes (resulting in their loss of function) or to DNA/RNA (disrupting their ability to produce proteins or replicate cells), which is what makes them toxic. They disrupt the normal functioning of the body producing side effects.

(If you’re asking yourself why salt, which is water-soluble, doesn’t explode when it’s mixed with water, I found a video on YouTube explaining why. When salt dissolves in water, the water does break the salt’s elemental bonds. But when the sodium and chlorine chemically combined originally, the sodium gave one of its electrons to the chlorine. When water breaks them apart, the chloride ion keeps that extra electron, making both the sodium ion and chloride ion more stable than their native elements.)

Sodium Gives Valence Electron to Chlorine

Acute Toxicity

Acute toxicity refers to the capacity to produce harmful effects from a single dose in a relatively short time, from minutes to about two weeks. Testing is normally done on rats or mice, so dosage information is approximated by taking the amount of material that caused the reaction per tested animal’s body weight and scaling it up for humans.

Median Lethal Dose LD50 (oral/skin – mg/kg of body weight) or LC50 (inhalation – mg/m3 of air for solids, ppm for gases): dose that kills 50% of tested animals
Lowest Lethal Dose LDLo / LCLo: lowest dosage known to have killed an animal
Lowest Toxic Dose TDLo / TCLo: lowest dosage known to have resulted in any kind of toxic effect other than death

The Acute Toxicity Rating System breaks this out into:

Highly Toxic: LD50 < 50mg/kg
Toxic: 50mg/kg < LD50 < 100 mg/kg (not in official system, but necessary for very dense metals/metalloids)
Moderately Toxic: 100 mg/kg < LD50 < 500 mg/kg
Low Toxicity: LD50 > 500 mg/kg

Chronic Toxicity

Acute toxicity refers to the short-term effects of a single exposure to a toxic mineral. Chronic toxicity is the long-term effects of multiple, smaller exposures as the poison builds up on the body.

Changes in the Body

Carcinogenic: causes cancer

Mutagenic: causes genetic mutations

Reprotoxic: damages the reproductive process

Risk Assessment

People who work in the mining and stone industries are at a much higher risk than mineral collectors. If you only handle solid pieces, your risk is very low. Your biggest concerns will be cleaning minerals and accidental ingestion by small children or animals. Those that do lapidary work will need to be concerned about inhalation and ingestion of rock and mineral dust as well.

Types of Toxicity

Radiotoxicity

Radioactive minerals are extremely rare. While there are a number of radioactive elements, radium, thorium, and uranium are the most common found in highly radioactive minerals. Sometimes in minerals containing rare-earth elements (REE) , the REE may be replaced by thorium, or more rarely, uranium, making them radioactive.

Radon is a byproduct of radioactive mineral decay and is radioactive itself. Radon gas is already in your homes from natural sources seeping into the tiny cracks in your home. If you plan to store radioactive minerals, it would be a good idea to keep a radon detector in your home to monitor buildup. Radon gas is heaver than air, but unlike carbon monoxide, it does not sink and stay low to the ground. It’s easily moved by the air currents in your house.

How Radon Enters Your Home

Source: EPA

Thorium (Th)

Uranium (U)

Radium

These are the rare-earth elements:

Radioactive minerals are most frequently found in these types of rocks:

Radioactive Mineral Hosts - Uranium

Igneous Rocks	Abundance	Metamorphic Rocks	Abundance	Sedimentary Rocks	Abundance
Syenites and phonolites	0.1–26 ppm	Low-grade	<1–5 ppm	Shales, clays, mudrocks	1–5 ppm
Granites and rhyolites	2–50 ppm	Medium-grade	<1–5 ppm	Black shales (organic-rich)	2–1250 ppm
Intermediate Rocks	1–6 ppm	High-grade	<1–7 ppm	Phosphorite-black shales	≤700 ppm
Basalts and other mafic rocks	0.1–1 ppm			Sandstones	0.5–4 ppm
Ultramafic	0.001–1 ppm			Limestones, dolomites	<0.1–9 ppm
				Coals, lignites, peats	1–6000 ppm
				Pure evaporates	<0.1 ppm

Source: Earthwise British Geological Society

Radioactive Mineral Hosts - Thorium

Igneous Rocks	Abundance	Metamorphic Rocks	Abundance	Sedimentary Rocks	Abundance
Syenites and phonolites	0.7–35 ppm [typically >10 ppm]	Highly variable, typically	6–10 ppm	Shales, clays, mudrocks	10–13 ppm
Granites, rhyolites and intermediate igneous rocks	8–56 ppm			Pelagic clays and siliceous oozes	2–30 ppm
Basalts and other mafic rocks	0.1–4 ppm			Sandstones	1–7 ppm
Ultramafic	<0.1 ppm			Phosphorites	1–5 ppm
				Limestones, dolomites	<0.05–3 ppm
				Bauxites	~50 ppm

Source: Earthwise British Geological Society

Radium comes from Radian Barite.

Radian Barite

Radioactive Minerals

This is a non-exhaustive list of minerals containing significant amounts of radioactive isotopes of elements, uranium and thorium. They emit alpha, beta, and gamma ionizing radiations, as well as radon.

There are three concerns with collecting radioactive minerals.

Direct radioactivity from the minerals

Fine radioactive dust particles

Radon gas produced by the minerals

Irradiated Gemstones

Finally, many gemstones are irradiated to enhance or change the color. This can make them slightly radioactive. If you have concerns about wearing irradiated jewelry, make sure to purchase them from a legitimate source that is subject to the United States Nuclear Regulatory Commission and don’t wear it as your every day jewelry. Do not trust the sellers on eBay or Etsy, especially those from overseas. One sent me an irradiated gemstone as a “free” gift that is much more radioactive than normal.

Irradiated Gemstone

Preventative Measures

Keep distance or a barrier between you and the material

Avoid handling as much as possible
Use handling equipment when possible
Work at arms’ length
Wash your hands after handling the material
Wear nitrile gloves when handling the material

Smaller specimens have less radioactive material

Keep your specimen as small as you can
Keep highly active, large or stock specimens in shielded storage

Do not allow the material to get inside your body

Do not handle the material near food or drink or where they are prepared or eaten
Do not lick, sniff, or eat the material
Do not cut, grind, or polish the material
Keep the material in a closed container and locked away
Keep material away from children / pets

The build-up of radon gas is a concern

Typical house ventilation is sufficient for small specimens
Vent your container away from your face before opening

Physical Toxicity

The three types of physical toxicants are:

Coal

Asbestos

Silica

Coal

Coal workers’ pneumoconiosis or black lung disease is caused by long-term exposure to coal or graphite dust and is not a concern for mineral collectors.

Asbestos

Asbestos is a group of six naturally occurring minerals made up of heat-resistant fibers. Asbestiform minerals are ones that form into microscopic fibers and include non-asbestos minerals.

Asbestos is most frequently found in: serpentinites, altered ultramafic rocks, and some mafic rocks.

Asbestos minerals are frequently embedded within other minerals trapping the microscopic fibers. For instance, Tiger’s and Hawk’s Eye contain crocoidolite, but it’s embedded within the quartz, so the asbestos itself is not a concern (see below for quartz toxicity).

Prolonged or repeated inhalation of microscopic fibers can lead to asbestosis, mesothelioma, or lung cancer. As long as you aren’t storing large quantities of asbestiform minerals, you should be safe.

Asbestos / Asbestiform Minerals

This is a non-exhaustive list of asbestos/asbestiform minerals.

Silica

Silica occurs in three different forms:

Crystalline

Microcrystalline (aka cryptocrystalline): minute quartz crystals bonded together with amorphous silica

Amorphous: non-crystalline

Crystalline Silica Minerals

Crystalline silica forms in seven different ways depending on the temperature of formation. The main three are:

Cristobalite

Tridymite

Quartz is found in nearly all acid igneous, metamorphic, and sedimentary rocks. Cristobalite occurs in acidic volcanic rocks. Tridymite occurs in cavities in felsic volcanic rocks.

Prolonged or repeated inhalation of crystalline silica dust can lead to silicosis or lung cancer as the crystals get trapped in the smaller spaces of the lungs. Silicosis is a form of pneumoconiosis marked by inflammation and nodular lesions in the upper lobes of the lungs.

Signs and symptoms of silicosis include:

Dyspnea (shortness of breath)
Cough
Fatigue
Tachypnea (rapid breathing)
Loss of appetite and weight loss
Chest pain
Fever
Gradual darkening of skin
Gradual dark shallow rifts in nails
Cyanosis, pallor
Cor pulmonale (right ventricle heart disease)
Respiratory insufficiency
Death

The microcrystalline and amorphous varieties do not pose this same hazard (though it is possible for heated amorphous silica to convert to tridymite or cristobalite). Non-crystalline silica doesn’t get trapped in the lungs like the crystalline does and the microcrystalline versions are compacted and trapped within amorphous silica.

Microcrystalline version of quartz include:

Agate

Chert

Flint

Jasper

Onyx

Preventative Measures

Asbestos

Keep out of reach of children and animals
Do not lick, ingest, or sniff
Do not generate dust by cutting, grinding, or polishing
Do not put your hand to your face or eat/drink/smoke while manipulating samples
Wash your hands immediately after handling
Store specimens in airtight containers and ventilate outdoors

Silica

Wet cut, grind, and polish quartz and quartz-rich rocks
Work with these outside your home in a well-ventilated area
Keep the workspace wet to prevent dust from going airborne
Wear an N95 respirator
Wear disposable clothes or wash them immediately
Shower before entering your home

Chemical Toxicity

Three routes of entry into the body are of concern for chemical elements:

Skin Contact

Ingestion

Inhalation

Skin Contact

For skin absorption, highly water-soluble toxic minerals are the only type you really need to worry about. None of the toxic minerals that have bioavailable toxic elements are used as gemstones. If you plan to wear or carry (for instance, as a worry stone) something a little more unusual, make sure to look up whether it is safe.

Highly Water-Soluble Toxic Minerals

Preventative Measures

Keep away from water or moisture

Wear gloves when handling

Wash hands thoroughly after handling

Ingestion

Hopefully mineral collectors aren’t prone to eating their rocks, but in the case of accidental ingestion by children or animals, here are the most toxic elements in order of toxicity and their associated bioavailable minerals, also in order of toxicity.