From Pathfinder Rage of Elements, which isn't enabled.

Precious Alloys

FEAT 5

Choose cold iron or silver. Your melee unarmed attacks have the special properties of a weapon made of that metal. If you are at least 13th level, you can choose adamantine instead of just cold iron or silver.

Special You can take this ancestry feat multiple times, choosing a different metal each time.

Pathfinder Rage of ElementsOGL