Minecraft wiki entry for Rock, associated text: Cobblestone – a block of cobbles that drops from mining stone; found naturally where flowing water meets flowing lava; widely used in crafting
Flint – a rock that drops from gravel; useful in crafting arrows and starting fires
Obsidian – a hard black blast-proof rock found where lava is flash-cooled by water; useful for crafting enchanting tables, ender chests and beacons, traveling to the Nether and summoning dragons