A lightweight metallic nanomaterial used in structural 3D-printing.
Nanite production will typically outstrip iron mining. Assuming full staffing, a single T3 iron mine will produce enough iron for a T2 nanite processor to manufacture one nanite per in-game hour, with the ideal situation being two iron mines per nanite processor (fully staffed).
Always prioritize copper over iron, as it is 10% faster to fabricate than iron. Kelko sludge should only come in last as an emergency, such as in Hyla's Crescent, as it takes 800% longer to process than iron.