While in the ground, coal looks similar to flint. Coal looks like black, squiggly ovals. Coal in an inventory, however, looks like just a lopsided pentagon (a square with a triangle on top).
Where Found
Deposits of coal are common underground, where stone is found. It is more common near the surface of the world. Before Game updates 2023/1010, coal could be warped in from the Diamond Portal. Players have made the mistake of thinking flint was coal; they look very alike, but coal cannot be found within dirt
Coal can also be bought from the Trade Portal
Crafting
Coal is required to convert an iron ingot into a steel ingot in a furnace or electric furnace, taking two in a normal one and one in an electric one. Prior to version 1.4, crafting steel required five coal.