The Source
The ore, mined from the dwarven holds and the surface seams of the old world — the floor of the metal ladder, and the one the anvil-singers start with.
The Yield
A seam gives a season's labor for a forge's load; the hold gives a year for a master's load.
In the Workshop
The iron is the argument every other metal has to win: it is everywhere, it is cheap, and it is the one the world is made of. A masterwork in iron is a story event, because the iron is the one that was already the default.
Cost band: apprentice (raw) — the base of the price ladder — on the ladder in The Maker's Hand, the material is the floor, and the floor is the one the mine or the marsh or the tree has to give. Recipes that take it: forging, smithing, runecraft