Copper

Copper was a metallic element. Its chemical symbol on the periodic table was Cu. (AUDIO: Escape Room)

Properties
When oxidised, it would turn green in a process called verdigris. (PROSE: Verdigris)

Cupronickel was an alloy of copper and nickel. (PROSE: All I Want for Christmas)

Use
Flinthair's axehead was made of copper. (PROSE: Loop the Loup)

When the Timewyrm possessed Dumuzi, she had him place copper around the walls of Kish, turning it into a giant radio transmitter. (PROSE: Timewyrm: Genesys)

Copper was used in the casings of many Earth bullets. When the Sontarans invaded in 2009, they used Cordolaine signals to excite the copper, causing bullets to stick in the barrel. (TV: The Sontaran Stratagem / The Poison Sky)

Copper was magnetically attracted to argonite, and would interfere with computer systems which used the metal. Milo Clancey deployed two tons of copper needles from the LIZ 79 to immobilise Ian Warne's spacecraft, which was about to fire a missile at him. (TV: The Space Pirates)

Kaleds had copper in their blood, giving it a green colour. (AUDIO: Corruption)