Iron working

A new metal
''What if there is more metals we havn't discovered yet? Some red stones seem to hide a different metal we know nothing off, but that seem to be considerably harder to extract and work with. However making bronze out of Copper and the rarer Tin is a complicated process that makes us rely on 2 different metals and dependent on trade. Maybe this new metal, while harder to extract, could be an alternative to Bronze?

Potential Requirements

 * Unknown

Info
Iron working is a late-game tech that allows you to make use of iron and enable several new buildings.