34Se Selenium

Year Discovered


Discovered By

Jons Jakob Berzelius of Sweden

Biological Rating

Necessary for all life.


Named from the Greek word meaning “moon,” selenium is a metalloid element that occurs in at least three forms: a gray metallic form, a deep red or black powder, and a red crystalline form. It is stable in air, water and most acids, but reactive to alkalis. Selenium conducts different amounts of electricity, depending on how much light is hitting it. It also can convert light to electricity. Consequently, it is used in photoelectric cells, light meters, TV cameras, photocopiers, solar cells and semi-conductors. Selenium can convert AC electric current to DC current and is used in such converters. It is the active ingredient in dandruff-prevention shampoos, and is a cutting agent in rubber. Selenium can remove color from glass, or it can add a red color to it. It is also used in alloys, especially with steel.

Biological Benefits

In tiny amounts, it is essential to some species, including humans. Its role seems to be that of a cleanser or protector; it shields against cancers and other diseases by scavenging for free radical oxidants and some heavy metals. Natural selenium deficiency in rocks and soils may be related to the incidence of stroke in humans, and excess selenium can cause deformities and disease in animals.

Role in Life Processes

Necessary for full health in plants and animals.

Percentage Amount in the Human Body: 0.00002%


Selenium minerals are rare, and although selenium-rich ores exist, few are mined exclusively for the element. Most selenium is obtained as a by-product of copper ore processing. Selenium is occasionally found in pure form. It occurs in the rare minerals clausthalite and crooksite. Despite the name, the mineral selenite actually contains no selenium. Selenium is mined in China, Japan, Russia, Germany, Belgium, and other countries, including the United States.