Minecraft wiki entry for Things_not_to_do, associated text: Glass does not drop itself when broken unless the player uses a tool enchanted with Silk Touch. Thus, players should be careful where they put glass, because if placed it in the wrong place and broken, it cannot be recovered. For this same reason, the player should also avoid holding glass in the hotbar, unless they plan to use it soon. This same advice is recommended for glass panes and glowstone.