Copper ore

Copper ore is a mineral found underground that can be used to make tools and armor.

Obtaining
Copper ore will only drop if you mine with a flint pickaxe or better. If mined with anything lower than that, it will drop nothing.

Natural Generation
Copper ore only occurs around from the wall to slightly above water temple level. However, almost all of the copper ore be at the lower levels. On average, there are about 163 copper ores per chunk.

Veins can vary in size, but the most common is 5x5x5. Copper always comes in veins of 5 to 11 unless grass, flint, a tunnel, or another ore overlapped into it. Each block in the vein, which otherwise would be stone, has a random chance of being copper ore instead.

Trivia

 * Breaking it gives you the ore, making you have to melt it before it turns into a block.