Minecraft wiki entry for Gravel, associated text: When gravel falls on a player or mob, it can engulf the head, resulting in suffocation inside gravel until destroying the block, moving out of it, or dying. If falling gravel lands in a space occupied by a non-solid block (such as torches, slabs, rails, or redstone dust) or soul sand, it breaks and turns into a gravel item. Gravel falls slowly through a cobweb until it passes completely through, or until it touches any block, at which point it drops and becomes a gravel item.