Iron Ingot

Iron ingots are versatile metal crafting ingredients. They are most commonly obtained by smelting iron ore.

Mining
Mining a nether reactor core in the Pocket Edition will drop 6 iron ingots.

Iron golems
Iron golems drop 3-5 iron ingots upon death, regardless of the way they die. The looting enchantment does not increase the amount of iron ingots dropped.

Zombies
Zombies have a 8.5% chance of dropping 1 iron ingot, 9.5% with Looting I, 10.5% with Looting II, and 11.5% with Looting III.

Trading
Villager armorers, tool smiths, and weapon smiths buy 7-9 iron ingots for one emerald as their second tier trades.

Repairing
Chainmail helmets, chestplates, leggings, boots and iron helmets, chestplates, leggings, boots, swords, pickaxes, axes, hoes and shovels can be repaired with iron ingots in an anvil.

Trivia

 * The iron ingot is the most versatile item in the game, being used in 27 crafting recipes (28 as of 1.9). The second most versatile item is wood planks with 23 recipes.

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