Minecraft wiki entry for Things_not_to_do, associated text: Do not mine glowstone unless it can be collected safely by constructing a cobblestone platform underneath it. Otherwise, a ghast might blow up both the player and the cluster or the glowstone may fall a large distance or into a lava pool. Also, players should not go out of their way to find glowstone if they know where a witch hut is – the player can kill witches every so often to have a chance to get a little more glowstone. For those who have the patience, building a witch farm is worthwhile, and circumvents the danger of ghasts. But so long as the player is alert and has a Power I bow, they can kill Ghasts in one shot, making them much less dangerous.