Iron Ore

Iron ore is a mineral block which may be found underground. It is the most common mineral which may be used to make tools and armor.

Iron ore requires a stone, iron, or diamond pickaxe to successfully mine. It must then be smelted in a furnace to make an iron ingot; iron ingots can be used to make medium quality tools, armor, buckets, Flint and Steel and shears, as well as a compass. A full list of craftable items can be found at Crafting.

Iron ore is often used in player traps as it can be mined and replaced in its raw form.

Natural Occurrence
Iron occurs only around from bedrock to slightly above sea level(layers 1-65). However, almost all of the iron ore will be underground. It is found in approximately 0.72% of stone from rows 2-61. On average, there are about 78.8 iron ores per chunk. Due to being extremely common, iron veins are frequently seen at the boundaries of any hollow space such as caves and lava lakes, but they are no more common there than in any other volume of stone.

Veins can vary in size, but the most common size is 2x2x2. Iron always comes in veins of 4 to 8 unless dirt, gravel, a cave, or another ore replaced some. Each block in the vein which otherwise would be stone has a random chance of being iron ore instead. (Therefore, it is good practice to check around a located ore block for more ore, as ore blocks may be only diagonally adjacent rather than face-to-face.) If the vein intersects a cave or other structure, part of it may be replaced with empty air. Occasionally, two veins will form next to each other, making it look like more than 8 ores.

Edit: Whoever is the owner of the Wiki needs to check the math on just how much Iron Ore can be found. 0.72% of layers 2-61 (333,235.814 blocks per Xbox 360 world) does not even come out close to 78.8 per chunk (229,780.8 blocks per Xbox 360 world).

Trivia

 * In third person view, all ores being held by the player such as Diamond Ore, Gold Ore, or Redstone Ore, seem to look like the texture is reversed, like TNT.
 * Iron ore can rarely be seen from the surface.
 * Iron, coal, gold, diamond and redstone ores all have the same texture, with different colors of the spots being the only way to separate them.

Gallery
Eisen (Erz) Iron (Ore)/es Fer (minerai) 철 원석 IJzer (erts) Ruda żelaza pt-br:Iron (Ore)/ptbr Железо (руда) 铁矿石