Cobblestone

Cobblestone is a darker block, often looking like a roughly paved area. This block doesn't occur naturally on it's own, but makes great walls for constructions such as castles, towers and roads. In the survival and indev/infdev modes, you obtain cobblestone by mining stone. There is an alternative version of the block known as Mossy Cobblestone, available only in Creative mode.

History
Cobblestone was removed in 0.0.19a, but returned in 0.0.20a. It was removed due to lack of room in the UI. Because of its dark color it was often used in pixel art to represent darker colors until other, darker blocks like black cloth and obsidian appeared.