Sulphur


 * Not to be confused with Redstone, Redstone (Dust), Glowstone, or Glowstone Dust

Sulphur is not found naturally in the world of Minecraft. It can only be obtained through the killing of either Creepers or Ghasts. Sulphur can also occasionally be obtained by opening reward chests in dungeons. Creepers are less likely to drop sulphur if burned to death. Ghasts also drop sulphur, but because they float, there is a good chance the sulphur will fall into lava or into a place that cannot be reached.

Trivia
Sulphur was 'officially' referred to as gunpowder until the Beta's Item Naming update. In the "real world", sulphur is one of the ingredients of gunpowder, but is yellow and crystalline like Glowstone, while being grey and powdery like gunpowder in Minecraft. Silly Notch.