Tellurium

Tellurium is a brittle, silvery-white metalloid and one of the rarest stable elements in Earth's crust. Franz-Joseph Müller von Reichenstein discovered it in 1782 in a gold ore from Transylvania, and Martin Heinrich Klaproth later named it after tellus, Latin for Earth. It is recovered from the leftovers of copper refining.

Its biggest modern use is in cadmium telluride thin-film solar panels. Tellurium compounds also form the recording layer of rewritable CDs, DVDs and Blu-ray discs, and bismuth telluride powers thermoelectric devices that cool or heat when electricity flows, as in some portable coolers. A little tellurium makes steel and copper easier to machine.