Selenium

Selenium is a nonmetal that conducts electricity better when light shines on it. That property powered early light meters and photocopiers, and early experiments in sending pictures by wire. Jöns Jacob Berzelius discovered it in 1817 and named it after the Moon, selene in Greek, because it resembles tellurium, which is named after Earth. It is mostly recovered from the leftovers of copper refining.

Today selenium is used to remove the green tint from glass or to color it red, in some thin-film solar cells, and in metal alloys. Our bodies need tiny amounts to stay healthy, though larger doses are toxic.