Iron Ore

Iron Ore is an early-game ore that generates upon world creation on the surface, as well as in the Underground and Cavern layers. Its primary use is in crafting Iron Bars, which can then be used to craft the Iron tier of tools, weapons, and armor, as well as Buckets, Chains, and several other items. The equivalent of Iron Ore is Lead Ore, which will sometimes replace Iron in a world. Iron Ore has a small chance to appear as a bonus drop from Slimes.

As Iron Bars are needed to create an Iron Anvil, Iron Ore must usually be obtained before any weapons or armor can be created out of metal bars. While this can be circumvented by purchasing an Iron Anvil from the Merchant, that is generally inefficient, as it is not difficult to find 15 Iron Ore early on in the game.

Trivia

 * Iron Ore and Lead Ore are the only ores that do not have corresponding bricks or chandeliers (until Terraria 1.4 update).
 * Real is very malleable and susceptible to corrosion, generally making it infeasible for crafting tools. The use of iron in Terraria more closely resembles real-life.

History
Eisenerz Minerai de fer 철 광석 Iron Ore Железная руда 铁矿