Copper Ore

Copper is a material that can be mined with the pickaxe.

According to both Aaron Bishop and the material's image name in the game folder, ORECU-0.TGA, this is Copper, since Cu is Copper on the periodic table. Kickstarter update #8 confirms this here:

"Also decided to put in Copper and Tin ore, and dress up the other material types. Eventually want to make it so Copper and Tin picks can only dig through dirt -- to dig through stone you'll have to alloy the two to make a Bronze pick. Then something similar when it comes to mining deeper ores like Mithril.

-Aaron"

Copper, like all other ores, is currently unusable as of Alpha 37. In the future it may be possible to combine Copper with Tin to make Bronze, in order to create a pickaxe capable of digging through Stone according to Aaron. Any further uses are speculation at this point in time.