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Toxic Minerals

Chapter: Antimony | Arsen | Lead| Cadmium | Chrome | Copper | Nickel | Mercury


Minerals are inorganic chemical compounds that crystallize naturally. Many of these compounds can also be produced industrially. The sale of these industrial products is subject to the Chemicals Levy Ordinance, which stipulates, among other things, that toxic substances must be labeled and may only be sold with a safety data sheet.

In the mineral trade, a corresponding procedure has been unusual up to now, because minerals are usually in a different form than industrial chemicals. Depending on whether they occur as powdery coatings, well crystallized, or as inclusions in host minerals, they develop varying degrees of toxicity. Substances used in the chemical industry are usually powdered, which gives them a significantly larger surface area than their crystallized mineral kingdom counterparts. A larger surface area means a larger surface area for solvents to attack and thus a greater potential to be absorbed by the human body.

One gram of a well-crystallized mineral can potentially pass through the gastrointestinal tract without being dissolved and causing symptoms of poisoning, whereas one gram of mineral powder can potentially be toxic. On the other hand, natural minerals are rarely as pure as the industrial products. Incorporated impurities or decay products can both improve solubility and add up to the potential hazards of the individual chemical compounds present.

In order to estimate the potential hazard posed by a toxic or harmful mineral, the following factors must be considered:

1. Exposure

Depending on whether toxic minerals are present as powdery coatings, well crystallized, or as inclusions in host minerals, they develop varying degrees of toxicity.

2. Absorption

The route by which toxic substances come into contact with and are absorbed by the body is critical to their potential to cause harm. The most common routes of absorption are: skin (toxic by touch), respiratory system (toxic by inhalation of dust - important when working with stones), gastrointestinal tract (toxic by swallowing).

3. Dose

What quantities are ingested. Here it has proven useful to indicate the dose at which 50% of the test animals (dogs, rats, bacteria, fish) die (LD50). It is also useful to indicate the dose that is lethal when ingested via different absorption routes (LD-oral, LD-dermal, etc.) Unfortunately, such laboratory values are not available for all toxic minerals.

3. Contamination Time

Some elements such as lead and mercury, can accumulate in muscle or fat tissue or even in bones. Minerals containing such elements develop their harmful effects only in the course of longer periods of time (chronic poisoning).

Problematic Elements

It has been shown that especially minerals containing heavy metals such as antimony, arsenic, lead, cadmium, chromium, copper, nickel or mercury can have a toxic effect. The prerequisite for a health hazard is that the substances are absorbed by the human body. This can happen via the skin, the gastrointestinal tract or the lungs. Only the very few minerals containing heavy metals can be absorbed through the skin. These include some chromium compounds (e.g., lopezite), some nickel compounds (e.g., nickelin), and some mercury compounds (e.g., calomel).

Some minerals exhibit adverse health effects when swallowed and dissolve in stomach acid. These include some copper minerals (e.g., chalcanthite), some cadmium minerals (e.g., greenockite), and some lead and nickel compounds. In normal adult handling of minerals, ingestion is unlikely to be an issue. However, with small polished tumbled stones, it cannot be ruled out that they may be swallowed by children. Even when used for wellness and healing purposes, where the practice of soaking in water is becoming increasingly widespread, components of problematic minerals can enter the digestive tract.
However, by far the largest percentage of all heavy metal mineralization can only become a problem through the inhalation of dust that can occur during the processing or cleaning of mineral specimens.

Whichever way the mineral enters the body, the deciding factor for a toxic effect is ultimately the amount of the substance ingested. Some heavy metals are needed in low doses by the human body as essential trace elements to maintain health. In higher doses, they have exactly the opposite effect and have a toxic effect. These toxic levels are documented in the chemical industry's Material Safety Data Sheets (MSDS), which specify exactly what amount of the (powdered) compound showed a toxic effect in laboratory tests. The SDSs used for this article can be viewed on the Internet on the manufacturers' websites (see bibliography). Unfortunately, due to the sometimes great complexity of natural mineral compounds, corresponding laboratory values are not available for all heavy metal mineralizations.

An often underestimated factor is the contamination time, during which small doses are absorbed over a long period of time. Some elements, such as lead and mercury, can accumulate in bones, muscles and fatty tissue and only develop a rather chronic poisoning effect after a long time.

In total, more than 200 different minerals are found in nature, which under certain conditions can have a harmful effect on humans and nature. However, many of them develop their toxic effect only in contact over long periods of time or in massive inhalation of mineral dusts. They are therefore only relevant in connection with occupational safety measures in mining or processing plants.

However, a small group of minerals should also be considered by mineral collectors and dealers, so that exhibition, storage and care of the beautiful pieces can be done without harming health and the environment. The following selection was compiled according to two criteria:

  1. The mineral is offered in "visible" quantities in the trade. Mineralizations that are very rare or found only in microscopic size were not considered.
  2. For the chemical compound corresponding to a particular mineral, a safety data sheet (SDS) exists from the chem. Industry.


More than a hundred antimony minerals are known in mineralogy, but only the antimony sulfide antimonite (stibnite, Sb2S3) and the antimony oxide valentinite (Sb2O3) are of commercial importance. Both compounds are insoluble in water and weak acids and are hardly absorbed through stomach and intestinal walls. Because of the low absorption capacity, the toxic effect when swallowed is limited to damage to the gastrointestinal tract, which can lead to nausea, vomiting and diarrhea. It should be borne in mind, however, that natural antimony compounds can almost always also be contaminated with other heavy metals such asarsenic and lead, which often have a much more toxic effect than the antimony compounds themselves. In general, trivalent antimony compounds are about ten times more toxic than pentavalent ones.

Caution should be exercised when coming into contact with dust containing antimony, which can damage the eyes (conjunctivitis) and skin (dermatitis, keratitis) and lead to hemolysis (separation of red blood cells). In addition, damage to internal organs (pulmonary edema, liver cirrhosis, kidney defects, cardiovascular) and bone marrow may occur.

Handling of antimony minerals

Antimony-containing minerals are relatively unproblematic to handle. Due to their largely insolubility in water and only very limited absorption of antimony in the human gastrointestinal tract, there is no acute hazard in handling and trade.

When working with allemonite or coming into contact with dusts containing antimony, a mouth guard should be worn.



Realgar crystals can decompose in air to toxic arsenolite. Therefore, they should always be stored in well-sealed plastic jars

Arsenic rarely occurs in nature in pure form, but almost always in combination with other elements such as sulfur (sulfides) or oxygen (oxides).

Solid arsenic and arsenic sulfides are only slightly soluble in water and can therefore hardly be absorbed by the body. A serious danger, however, is the possible formation of the arsenic(III) oxide arsenolite, which can bloom as a white coating on digested arsenic and arsenic sulfides due to oxidation processes in the air. Affected are the rather rare arsenic sulfides duranosite (As4S), dimorphine (As4S3) and uzonite (As4S5) as well as the more common minerals realgar / pararealgar (As4S4) and orpiment (auripigment) (As4S6). Especially realgar and orpiment tend to such oxidation processes. Their old German names "Rauschrot" (rush red) and "Rauschgelb" (rush yellow), possibly refer to the toxic effect of the decomposition product arsenolite. Both minerals are toxic when mineral dust is inhaled or swallowed and very toxic to aquatic organisms.

Compounds of copper, silver or iron with arsenic and sulfur such as tennantite (Cu12As4S13), proustite (Ag3AsS3) or arsenopyrite (FeAsS) can also have a toxic effect due to the secondary formation of arsenolite. In case of fire, arsenic sulfides decompose to arsenolite and sulfur dioxide. For these reasons, all arsenic sulfides are classified as potentially toxic and harmful to the environment.

Arsenolite (As2O3), under the name arsenic, has been known for centuries as a very potent poison. It is clearly carcinogenic. Because of its good water solubility (37.0 g/l), it can be readily absorbed by the body both through the gastrointestinal tract and by inhaling dusts through the lungs. The orally absorbed lethal dose for humans can be as low as less than 0.1 g. The arsenic compound can also be slowly absorbed through the skin, causing significant burns.

Acute poisoning manifests itself after a few hours by massive diarrhea and vomiting. Later, severe abdominal pain and cramps in the extremities occur. Clouding of consciousness, visual disturbances and physical weakness increase steadily until death finally occurs.

More frequent ingestion of small amounts of arsenolite can lead to chronic poisoning. The consequences are nerve damage, weakness, numbness and tingling of the limbs, dark skin discoloration, bone marrow regression, and liver changes.

Other arsenic oxides such as the water-insoluble arsenates annabergite (Ni3(AsO4)2, durangite NaAlF(AsO4), erythrin Co3(AsO4)2, olivenite Cu2(OH)(AsO4), rauenthalite Ca3(AsO4)2 and scorodite Fe(AsO4) are less toxic because the included arsenic is present in a different oxidation state. They become problematic when their dusts are inhaled, as they are clearly toxic and carcinogenic in powder form. They are even very toxic to aquatic organisms and are therefore classified as highly hazardous to water.

Handling of arsenic minerals

Because of the possibility of contamination with arsenolite, native arsenic and arsenic sulfides should always be stored in airtight plastic boxes and out of reach of children.

To prevent accidents, gloves and mouth guards should be worn when handling arsenic compounds. In case of fire, a gas-tight full body suit is required. Release into the environment must be avoided; if necessary, arsenic-containing minerals must be disposed of as special waste.


Lead occurs in nature almost exclusively as a lead(II) compound. The element is a cytotoxin that causes various harmful effects in organs and organ systems depending on the dose and time. Acute lead poisoning, manifested by gastrointestinal symptoms, severe abdominal cramps ("lead colic"), slow pulse and high blood pressure, is extremely rare.

As a rule, the disease progresses chronically due to accumulation of lead in the bones and internal organs. By preventing the incorporation of iron into the hemoglobin molecules, the hemoglobin synthesis may be disturbed, resulting in reduced oxygen transport. The consequences are headaches, fatigue and emaciation. The central nervous system and vitamin D metabolism can also be disturbed. Chronic lead poisoning can lead to damage to the child in the womb, impaired reproductive ability and impaired child intelligence development.

Dried lead is classified as nontoxic to humans. However, it can form a poorly water-soluble layer of lead carbonate (cerussite) when exposed to air, which can dissolve in the stomach when ingested orally, releasing lead ions. Lead dusts, which can be ingested or inhaled, are also toxic.

Fortunately, most lead compounds are not water-soluble, so acute exposure occurs primarily when lead-containing dusts are inhaled, which can also cause them to enter the gastrointestinal tract.

This applies, for example, to lead oxide minium (Pb3O4), which is known as "lead minium" as a rust inhibitor and was banned a few years ago because of its toxicity. The lead sulfate anglesite (PbSO4), the lead vanadate vanadinite Pb5[Cl,(VO4)3], the lead molybdate wulfenite (PbMoO4), and the lead sulfide galenite (galena, PbS), are also toxic only in powder form, but not as well-crystallized crystals. Galena is often mixed with the lead(II) carbonate cerussite (PbCO3), which can form as whitish-gray to brown coatings called lead earth. If this admixture is fine crystalline, it is called black lead ore. In this fine crystalline, powdery state, the risk of respiratory contamination is particularly high. Cerussite, although insoluble in water, decomposes rapidly in gastric acid and can thus release its high lead dose.

All lead dusts are very toxic to fish and other aquatic organisms and are therefore classified as environmentally hazardous.

Handling of lead minerals

Contamination by lead-containing dust when handling lead minerals should be prevented by wearing a mouth guard. Lead minerals should be disposed of as hazardous waste, if necessary. Release into the environment must be avoided.


The pH value of the surrounding medium is decisive for the bioavailability of cadmium. With increasing acidification, sparingly soluble oxides and sulfides change into water-soluble Cd ions. This leads to poor solubility in gastric acid, allowing cadmium ions to enter the bloodstream. The most important natural cadmium compounds are the cadmium sulfide greenockite, the cadmium oxide monteponite, and the cadmium carbonate otavite.

Greenockite (CdS) can occur, for example, as a secondary mineralization in the form of yellow to yellow-brown crusts and coatings on sphalerite (zincblende, ZnS) or as a coloring compound in yellow smithsonite (ZnCO3). Its use as a yellow pigment in the paint industry is now banned because of its toxicity. Greenockite is insoluble in water, but reacts with stomach acid when swallowed, releasing toxic cadmium ions. Greenockite dust is classified as toxic. In case of fire, greenockite decomposes to highly toxic cadmium oxide (monteponite).

The hazard potential of monteponite (CdO) is mainly due to inhalation of dust during cleaning or processing of mineral specimens. This also applies to the mineral otavite (CdCO3), where there is also a risk of skin absorption (harmful to health on contact with the skin).

By accumulation in internal organs, cadmium can cause chronic damage to kidney, liver and bone marrow, which can also be irreversible. Impairment of reproductive ability and damage to the child in the womb cannot be ruled out. Long-term adverse effects may occur in aquatic environments.

Handling of cadmium minerals

To prevent hazardous situations, a mouth guard should be worn when cleaning or handling mineral specimens containing cadmium. Protective gloves should be worn when handling otavite. The mineral must be kept out of the hands of children. Powdered cadmium compounds are highly hazardous to water and must therefore not be allowed to enter the sewage system. If necessary, they must be disposed of as special waste.


Lopezit ist giftig

Keep Lopezite out of the reach of children

Image: K. Sieber, www.makrogalerie.de

Chromium is required by the human body as an essential trace element. The toxicity of chromium depends on its valence: chromium(III) compounds have a low toxicity because they can only be poorly absorbed by the body. In contrast, orally absorbed chromium(VI) compounds have an extremely toxic effect. They have long been known to be carcinogenic and mutagenic and can cause inflammation of the eyes, skin and mucous membranes, as well as ulcers and eczema. A chronic course can lead to irreversible eye damage.

The chromium(VI) compound lopezite (K2Cr2O7) is often available in the mineral trade in the form of large, orange, artificially grown crystal specimens. In this form the mineral is very popular not only with children. The mineral is very soluble in water (1020 g/l). Contact can cause burns to the skin and mucous membranes, which is why it is classified as very toxic. Skin contact can also cause chromium allergies. There is a risk of serious eye damage. Inhalation of dust is carcinogenic and can cause hereditary damage.

The orange-red lead chromate crocoite (PbCrO4) is a secondary mineral that can form, for example, by oxidation from galena. Under the name "chrome yellow" it used to serve as a brilliant yellow color pigment. Due to its toxicity and today it is almost completely replaced by organic color pigments. Since the mineral is hardly soluble in water (0.058 mg/l), it is not very toxic in well-crystallized form. In dust form, however, it has a clearly toxic effect. Due to the combination of the heavy metals lead and chromium(VI), there is a risk of cumulative effects of lead and the carcinogenic and mutagenic effects of chromium.

Handling of chromium minerals

When handling chromium(VI) minerals, rubber gloves and a dust mask should not be avoided. Care should be taken not to rub eyes with contaminated fingers and not to eat or smoke while working. Lopezite should always be stored in airtight plastic boxes and out of reach of children.

Lopezite and crocoite are powerful accelerants of fire. Therefore, they should be kept away from flammable objects. In the event of a fire, the toxic fumes generated must be taken into account by wearing special protective clothing (gas-tight full-body suit).

Because of their strong toxicity to aquatic organisms, they are classified as highly hazardous to water. Consequently, release into the environment must be avoided. If necessary, the mineral and its container must be disposed of as hazardous waste.



Chalcanthite, artificially grown

Image: K. Sieber, www.makrogalerie.de

As a vital trace element, copper is a component of many enzymes. The daily requirement of an adult human being is about 2 milligrams.

If not treated properly, copper compounds can lead to symptoms of poisoning such as nausea, vomiting and diarrhea. Children are particularly at risk, as they are much more sensitive to copper overdoses than adults. Copper is stored mainly in the liver. Chronic poisoning causes damage to the liver and kidneys and can also lead to death in young children.

Dried copper is physiologically harmless and is classified as non-toxic. In a mineral collector's normal handling of gediegen copper, poisoning is virtually impossible.

Some copper compounds can cause health problems if swallowed or inhaled as dust. Because of the harmful dust and environmentally damaging grinding water, the copper hydrogen carbonates azurite (Cu3(CO3)2(OH)2) and malachite (Cu2(CO3)(OH)2) are no longer processed in Germany. Accidental ingestion causes decomposition in the stomach, which can lead to nausea, vomiting and diarrhea.

The bright blue copper sulfate chalcanthite (CuSO4 · 6 H2O) is often offered in the mineral trade in the form of large, artificially grown crystals. It is very soluble in water (316 g/l) and is a strong emetic. It may also be carcinogenic or carcinogenic. When exposed to air, it slowly decomposes under water release to form pale, loose, powdery coatings.

Some copper minerals are used as pesticides. The copper(I) oxide cuprite (Cu2O) is used for antifouling marine coatings because the dissolving copper kills algae and other aquatic organisms. The copper(II) oxychloride atacamite (Cu2Cl(OH)3), which often occurs in association with chrysocolla, is used in agriculture as a plant protection agent (fungicide). Both minerals are harmful to human health when swallowed and when dust is inhaled.

Handling of copper minerals

The above copper compounds should be kept out of reach of children. To counteract decomposition, chalcanthite should be stored in an airtight container.

Copper minerals are very toxic to aquatic organisms. They may cause long-term adverse effects in water bodies. Water-insoluble copper minerals in powder form are also considered to be highly hazardous to water and must not be allowed to enter groundwater or sewage systems, even in small quantities.



Nickel magnesite can release nickel in an acidic environment

Image: K. Sieber, www.makrogalerie.de

On the one hand, nickel is a trace element that is required in the human organism in very small quantities (daily requirement 25-30µg). On the other hand, it is the trigger for contact allergies in the form of reddened skin or weeping pustules in 7-10% of women and 1-2% of men. In affected people, continued contact with nickel and nickel compounds can lead to chronic diseases.

The nickel compounds found in nature are very difficult or impossible to dissolve in water. Therefore, they can only be absorbed by the body if they enter the lungs or stomach as dust. In this case, poisoning symptoms such as nausea, abdominal cramps, dizziness, faintness and diarrhea may occur. In general, however, nickel poisoning is extremely rare.

The most important nickel ores are nickelin (NiAs) and millerite (NiS). Both are classified as toxic in powder form if swallowed or inhaled in dust. If their dust gets on the skin, it can cause contact allergies.

Nickel carbonate (NiCO3) is a constituent of the minerals hellyerite (NiCO3·6H2O), Ni-magnesite (Ni,Mg)CO3, which is also known by the misleading trade name "lemon chrysoprase," and gaspite (Ni,Mg,Fe)CO3. All 3 variants are insoluble in water, but dissolve relatively easily in stomach acid and release nickel. Therefore, they are harmful to health when swallowed or when dusts are inhaled. In addition, sensitization by skin contact is possible. There is a suspicion of a carcinogenic or cancer-promoting effect.

Handling of nickel minerals

When handling nickel compounds, attention should always be paid to allergic reactions. If they do not occur, handling is relatively problem-free. Nickel compounds are very toxic to aquatic organisms and highly hazardous to water. They should not be allowed to enter groundwater, bodies of water or sewers, even in small quantities.


decomposed cinnabar with globules of elemental mercury

In nature, solid mercury is usually associated with cinnabarite (HgS). When absorbed through the digestive tract, the liquid metal is relatively harmless. However, it tends to evaporate already at room temperature. Inhaled vapors have a strong toxic effect and lead to nausea, vomiting, abdominal pain, bloody diarrhea and loosening of teeth.

Dusty mercury compounds can be absorbed through the lungs, skin, and stomach. Some are corrosive to skin and mucous membranes. If swallowed, they can cause pharyngitis, difficulty swallowing, drowsiness, vomiting, abdominal pain, circulatory collapse and shock. The major hazard is the accumulation of mercury in fat cells, tissues and organs. Even small amounts appear to have effects on embryonic development. Chronic effects on the nervous system have also been demonstrated.

The most common mercury compound is the mercury sulfide cinnabarite (HgS). It is insoluble in water and therefore harmless as a compact crystal. Cinnabarite dust, however, can also be absorbed through the skin and is classified as very toxic if swallowed or inhaled. Tiny mercury droplets may be present on cinnabarite specimens, giving off highly toxic mercury vapors.

Another mineral that is relatively harmless when fresh and increases dramatically in toxicity through decomposition reactions is calomel (HgCl). In its pure state, it is an only slightly water-soluble (2.3 mg/l) white to light gray or yellowish mineral that is harmful to health if swallowed.

In light, it gradually turns dark to black as it decays to elemental mercury and mercury(II) chloride (HgCl2). Both decay products have a much greater hazard potential than the parent product. Mercury(II) chloride is about 250 times more toxic than the original mercury(I) chloride. The substance is highly soluble in water (74 g/l) and can also be absorbed through the skin. It is very toxic if swallowed and causes chemical burns.

Handling of mercury minerals

Rubber gloves should be worn when handling the mercury minerals described. Food ingestion and smoking should be avoided. Minerals should always be stored in airtight plastic boxes and out of reach of children.

All mercury compounds are very toxic to fish and other aquatic organisms and are classified as environmentally hazardous. Therefore, release into the environment should be avoided. Minerals containing mercury must be disposed of as hazardous waste.


The above examples show that it is often not sufficient to know the health hazard of the pure substance. It is equally important to include impurities and decay products in the considerations. Thus, the toxicity of heavy metal mineralizations is often difficult to assess without extensive knowledge of the chemical, physical, and medical relationships. Many factors affecting bioavailability play a role. Therefore, the toxic studies of the chemical-pharmaceutical industry can only be applied to minerals to a limited extent.

In fact, "normal" handling of minerals containing heavy metals very rarely leads to acute symptoms of poisoning. However, in the case of improper handling, it is conceivable that the living or exhibition area may become contaminated with heavy metals. Elevated mercury, cadmium or lead levels are not particularly desirable in living areas. Therefore, corresponding mineral pieces should be stored in plastic boxes or under glass as a precaution.


GESTIS-database of the Institute for Occupational Safety and Health of the German Social Accident Insurance (IFA).


Autor: Dipl.-Min. B. Bruder