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 is often found abundantly in mines in various boxes, on the floor and at the entrances. there is also coal found inside of The Riken and a furnace making it an ideal location to smelt. Coal can be used as a fire source after a fire has lasted 30 minutes.
A lump of coal.