Coal is an item obtained from ore. While it cannot be used to make armor, weapons, or tools, it can be used in many other useful things, a full list of which is included here. Coal is used as a Furnace fuel, and each peice melts 9 blocks. However, a block of coal is made out of 9 coal, but melts 80 items per block. So, each peice of coal going into a coal block is worth 10 items of smelting, which makes it a slightly more efficent way to smelt.