Charcoal

Charcoal is an alternative to Coal and works just the same. The higher the potential, the longer it burns. Although Charcoal doesn't last as long, it is easier to get and far more abundant. As long as there are trees there is an infinite supply of charcoal, and trees respawn. To create charcoal you need to have a lit fire or forge and wooden blocks. Place the blocks on the same tile as the fire and they will catch on fire, then burn into charcoal.