Charles wants to build a weapon that's secretly a weapon. That is, a hammer that's really a dart gun. He'll give you a recipe for an "Explosive Hammer Prototype".
Go out and harvest the goods he requested: You'll need 2 chert nodules, which are gound spawns in the Glittervein Mine or splitiron mine. You'll also need 2 amadou, which are ground spawn bracket fungus near the Abandoned Fungus Farm. There are several away from agro near 800.31,47.45,289.51 . Also, harvest 10 splitiron ore, which are mined from dark ore nodes.
Craft the hammer using 1 splitiron ore, 3 thalumbral roots, 3 umbrite and 5 thaumic coal.