Block of coal

The Block of Coal is an ore block which is made by crafting 9 coal together in a 3 X 3 grid. You can smelt 72 items with 1 Block of Coal, almost as long as a Lava Bucket.

Advantage

 * saves inventory space.
 * smelts more than a full stack.
 * Easy to acquire.
 * Can be placed on the map like any block.

Disadvantage

 * using it to smelt less than 16 items would be a waste.