Carbon is a native resource, one mined from bodies rather than made. It is found in every tier and is most plentiful in the Relay. A Smelter combines it with iron into steel plate, and a Refinery turns it into fuel, into polymer with hydrogen, and into fiber with polymer.
Carbon is very dark, so a carbon-coated surface absorbs more starlight and runs warmer. It never melts; it only sublimes, at a very high temperature.