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Kathy Feick

Selenium is a widely distributed mineral which is important to all life on Earth. It is found in most rocks and soils. It was officially named by Jons Jakob Berzelius in the year 1817. The word “selenium” was derived from the Greek word “selene,” which means “moon”. In its pure form, selenium may produce metallic gray to black hexagonal crystals, however these crystals are rare and it is usually found as a massive specimen. When crystals do form they are often fine and hair-like. In nature it is usually found combined with a sulphide or with silver, copper, lead and nickel minerals. Although selenium has a metallic lustre, it is not metallic in crystal structure or in bonding characteristics.

Selenium and health:

Selenium is an essential micronutrient in all known forms of life. It has many effects on the body including:

  • Prevent cellular damage from free radicals
  • Helps regulate thyroid function
  • May play a role in the immune system
  • In small amounts may reduce ones risk of cancer.
yellow selenite

Gypsum variety: Selenite. Red River Floodway, Near Winnipeg, Manitoba. Reimer Family Collection. University of Waterloo Earth Sciences Museum.

How do we consume sele​nium?

We receive the majority of selenium from our diets. The concentration of selenium in plants is dependent on the soils in which the plant grows or the animal is raised. It may concentrate up the food chain. Selenium occurs naturally in most rocks and soils, but it may also be released into the environment. Selenium dust can enter the air from burning coal and oil. This dust will eventually settle over the land and water. It can also enter the water from agricultural or industrial waste. Some selenium compounds will dissolve in water, while others will settle to the bottom as particles.

Dangers of selenium:

Selenium is an essential mineral to life on Earth but it does have dangers associated with it.

Over intake

Over intake of selenium may affect ones skin, development or reproductive ability. The general population is exposed to fairly low levels of selenium through food intake. Those who may be at risk to over intake include: those working or living near industries where selenium is produced, processed, or converted into commercial products; or those living in the vicinity of hazardous waste sites or coal burning plants. Selenium itself is not likely to cause cancer in humans, but the compound selenium sulphide likely does.

Under intake

Studies show that low levels of selenium are linked to a higher risk of cancer death. In addition, people with cancer often have low levels of selenium. You may have low levels of selenium if you:

  • Smoke cigarettes
  • Drink alcohol
  • Take birth control pills
  • Have a malabsorption syndrome (such as Crohn’s disease or ulcerative colitis)

Selenium deficiency is relatively rare in healthy people.


Selenium is a naturally occurring mineral element that is distributed widely in nature in most rocks and soils. That being said, it is scare to find in significant concentrations. Most elemental selenium comes from the refining of copper sulphides as selenium is a common trace element in these minerals. There is no real ore of selenium as it is far too rare. Some minerals which contain selenium as a major component include:

  • Berzelianite (copper selenide)
  • Clausthalite (lead selenide)
  • Eucairite (solver copper selenide)
  • Hakite (copper mercury silver antimony selenium sulphide)
  • Klockmannite (copper selenide)
  • Palladesite (palladium selenide)
  • Penroseite (nickel selenide)
  • Selen-tellurium (selenium tellurium)
  • Tiemannite (mercury selenide)
  • Umangite (copper selenide)

Notable occurrences:

  • Jerome, Yavapai County, Arizona
  • Gold Quarry Mine and Willard Mine, Nevada
  • Darwin Mine, California
  • Moctezuma, Sorona, Mexico
  • Monte Vesuvius, Italy
  • Harz Mountains, Germany
  • Potosi, Bolivia and Los Llantenes, Argentina


  • Most processed selenium is used in the electronics industry
  • As a nutritional supplement
  • In the glass industry
  • As a component of pigments in plastics, pains, enamels, inks and rubber
  • In the preparation of pharmaceuticals
  • As a nutritional feed additive for poultry and livestock
  • In pesticide formulations
  • In rubber production
  • As an ingredient in antidandruff shampoos
  • As a constituent of fungicides
  • Radioactive selenium in used in diagnostic medicine



Toxic Substance Portal-Selenium

University of Maryland Medical Center-Selenium

The mineral Native Selenium

Agency for Toxic Substances and Disease Registry (PDF)

Minerals Zone-Selenium