Coal is a special source of fuel in The Long Dark that enables players to reach high enough temperature to smelt materials to be used for crafting in a furnace. Coal can be found abundantly in mines in various boxes, on the floor and at the entrances. There is also coal and a furnace inside the Riken, which can be used for metalworking. Coal can be used as a fuel source after a fire has been burning for 30 minutes or longer.
A lump of coal.