Iron

Vanilla
on the Minecraft Wiki

Esteemed Innovation
Esteemed Innovation adds the Thin Plate and Nugget variations of the Iron material. The Thin Iron Plate can be created by melting Iron Ingots in a heated Crucible, and then pouring that molten metal into a Mold with a Plate Mold. Likewise, a Mold with a Nugget Mold can be used to cast Iron Nuggets.

Flaxbeard's Steam Power
Flaxbeard's Steam Power only adds the plate and nugget variations of the Iron material. The Iron Plate can be created by throwing Iron Ingots into a heated Crucible, and then pouring that molten metal into a Mold with a Plate Mold. Six nuggets are used in the creation of a Plate, which makes it unable to be used in other mod's recipes requiring their own Iron Plates.

GregTech 5
Small Iron Ore can be found at a height of 40 to 80 in the Nether Overworld and The End with a relative frequency of 16. Regular Iron Ore can be found sporadically inbetween mix veins at a height of 50 to 120 in the Nether and Overworld with a density of 3, a size of 32, and a relative frequency of 160, and sporadically around Iron mix veins at a height of 10 to 40 in the Nether and Overworld with a density of 4, a size of 24, and a relative frequency of 120.

Iron can also be obtained by breaking down the materials, , , , , , , , , , , , , , , , , , , , , , , , , , and , as well as through ore processing of , , , , , , , , , , , , , , , , , , , , , , , and.

Immersive Engineering
Iron Plates are used to create the Fluid Pipe.

Tesla Core Lib
Tesla Core Lib adds a Sheet, Powder, and Gear form of Iron.

Thaumcraft 4
Thaumcraft adds the Nugget variation of Iron as well as other metals. These nuggets can be crafted into wand caps, although (with the exception of Gold and Copper) higher-tier metals will need to be charged in an Infusion Altar.

Iron Ingot has 8 Metallum.