The history of selenium begins with a chemical factory at Gripsholm, Sweden. In 1817, chemists Jöns Jakob Berzelius and Johan Gahn were part-owners. They analyzed a red sludge that sometimes formed at the bottom of the furnace, and the chemists produced a substance that smelled like the already-known element tellurium.
Tellurium was an unlikely answer, though. Berzelius conducted extensive additional analysis on his substance and finally announced a new element. He named it "selenium" after the Moon, since tellurium is named after the Earth.
Mining and Production
Selenium as the primary component of a mineral is rare. There is a mineral called selenite, but it is a form of gypsum. Much more commonly, selenium is found as a trace component of sulfide minerals, particularly of copper, since it resembles sulfur chemically. Metallic selenium is produced at refineries as a byproduct of the electrolysis that produces copper. Annual production is a few thousand tonnes.
Properties and Uses
Selenium can exist in several forms, much like sulfur and carbon. It can be a black, glassy solid or a dark red powder (right). These forms are electrical insulators.
A grey form of selenium, though, is a semiconductor. In fact, it was the first useful semiconductor, for its conductivity increases when light falls on it. Alexander Graham Bell used grey selenium in his photo-telephone. Selenium was used for decades in light meters, electronic diodes, and rectifiers (right) until cheaper substitutes were developed.
The largest use of selenium is in glassmaking. Silicon glass tends to have a yellow tint, and selenium adds a red color that neutralizes that. Selenium is also used occasionally as a substitute for lead in alloys such as brass.
Selenium is an essential trace element in the diet but is toxic in moderate or larger amounts.