Here's why:

* Coal Formation: Coal forms from the accumulation and compression of plant matter over millions of years. It's essentially fossilized organic material.

* Carbon Content: Coal is rich in carbon, which is the key element that makes it combustible.

* Burning Process: When coal is burned, the carbon reacts with oxygen, releasing energy in the form of heat and light.

While other sedimentary rocks like limestone and sandstone may contain trace amounts of organic matter, they don't have the high carbon content needed to be burned as fuel.