Block of Coal

The block of coal is a mineral block that can also be used as a fuel.

Obtaining
Blocks of coal can be mined using any pickaxe. If mined without a pickaxe, it drops nothing.

Crafting
Blocks of coal can be crafted only from regular coal, not charcoal. It is crafted in the same way as other mineral blocks. In the legacy console edition, they are crafted with regular coal but drop charcoal instead.

Usage
Blocks of coal are often used to store coal in a compact fashion, or otherwise used as a fairly cheap construction block.

Fuel
Blocks of coal can be used as fuel in a furnace. One block of coal lasts 800 seconds, which smelts 80 items. This is ten times the duration of a single piece of coal and 1$1/9$ times as efficient as nine individual pieces of coal.

Trivia

 * Surprisingly, blocks of coal cannot be used as fuel for the minecart with furnace.
 * A full stack of coal blocks should smelt for 14.2 hours – over 42 Minecraft days. That is over fifty times as many items as a lava bucket. However, the player needs 576 coal or 9 stacks of coal to do this.