Selenium (Se)
Selenium (Se)
Discovered in 1817, selenium exists in several allotropic forms and with amorphous or crystalline structures. As a member of the sulfur family, it resembles sulfur in form and in its compounds.
Amorphous selenium is red (powder form) or black (vitreous form); the crystalline monoclinic version is deep red, and the stable crystalline hexagonal form is metallic gray. Selenium naturally contains six stable isotopes, and fifteen others have been found.
Selenium can be found in crooksite, clausthalite, and other rare minerals. It has both photovoltaic and photoconductive properties and is used in solar cells, photocells, and photographic exposure meters.
