Like Stripped Wood, Right Clicking on Stone Creates Cobblestone.

Rather than mining stone which turns into cobblestone, and then replacing it in place, right clicking on stone with a pick would convert it to cobblestone.  A lot of builders like to add cobble into caves and more natural builds to break up the monotony, but this would save some time.  It doesn't avoid any other blocks or tools needed, so I think it wouldn't change the dynamic at all, or let people have an advantage in the early game.