Jack-Hammer Block

I'm imagining a block that functions similar to a dispenser with shears, but using a pickaxe instead. It could break blocks in front of it when powered with a constant redstone signal lasting about as long as the normal mining animation. It could follow the same rules for mining as doing it in person, such as a stone pickaxe can't mine diamond or obsidian, etc. This way you could make automatic mining machines to use in cobblestone farms, rather than relying on duping TNT. It could also be used to dig tunnels in certain configurations.