Minecraft wiki entry for Surviving_in_a_single_area_indefinitely, associated text: You may notice that sometimes when you mine the cobblestone, the cobblestone item goes into the lava and burns up. If you have sufficient iron, place hoppers underneath where the cobblestone generates, all leading into a chest, so the mined cobblestone ends up in the chest. You could also use pistons to automatically push cobblestone away from the lava, letting you mine it without having to worry about any of it burning.