Selenium

Selenium  has a gray sheen  and is one of the chalcogens. Selenium occurs in several modifications, such as red selenium, black amorphous selenium and gray “metallic” selenium. The electrical conductivity can change depending on the exposure. Since Selenium is essential for all living things, it is often used as a food supplement and processed into feed and fertilizer additives. Other applications are in the manufacture of glass, in the manufacture of semiconductors, in cosmetics, as a toner for black and white printing and for the treatment of AIDS patients.