33As Arsenic

Year Discovered

1250 C.E. (probably known earlier)

Discovered By

Albertus Magnus (probably discovered earlier)

Biological Rating

Necessary for all life.


Arsenic’s name comes from the Greek term for an arsenic compound, orpiment (arsenic trisulfide). Arsenic is a metalloid element, which, like phosphorus, has two main forms. One is a brittle, gray metallic form and the other is a yellow, non-metallic solid. Yellow arsenic is the more reactive and unstable of the pair. Arsenic is stable, being unaffected by air, water, most acids and alkalis. Arsenic has no liquid phase; the solid sublimes directly into a vapor. Arsenic has semiconductor properties and is used in making transistors. It is also used in alloys, glass production, pyrotechnics and wood preservatives. An arsenic-gallium compound is used in making lasers. Arsenic was once used extensively in pesticides, but that use is subsiding owing to well known poisonous characteristics and danger to humans.

Biological Benefits

Arsenic is critical to some species, including humans. It is necessary for the functioning of the nervous system. A deficiency can lead to inhibited growth.

Role in Life Processes

Necessary to the full health of plants and animals.

Percentage Amount in the Human Body: 0.00001%


Arsenic occurs in pure form only in small deposits. It occurs in many minerals, and usually is obtained as a by-product from the mining, processing and refining of other minerals. Common arsenic-bearing minerals include arsenopyrite, conichalcite, enargite, lollingite (iron arsenide), olivenite and orpiment. Arsenic is mined in China, Chile, Russia, Mexico, and the Philippines.