Minecraft wiki entry for Combat, associated text: Sand or gravel aren't weapons in true sense, but they can be used to kill mobs. Best use is in caves — when the player are on a high place and the player have a mob directly below, they can place that block on a wall near where they are standing; the block will fall, and with right aim, it will fall on the mob, and thus suffocate it. However, killing with this weapon doesn't yield any experience, but that block will make the mob stuck, and the player can finish them with the sword.