Copper

Copper is, after iron, the most abundant ore on the Overworld; it is over 3 times as abundant as tin. It is used in Machine Frames and in the Crusher. Being the ingredient for the Crusher makes it a very important early-game ore, because, once you have the Crusher, you can double ores rather easily.

Uses
As stated above, Copper is used as an ingredient for some of the machines.

Copper is also a material used in 2 Alloys. When mixed with tin you get bronze, when mixed with zinc you get brass.