Coal

Coal is a mineral used to power electricity and/or heat.

Physical appearance
It is a black rock.

Season one
The basement of Col. Beauregard Sanders's mansion is full of it, as Scooby-Doo found out after falling down a ramp, which lead from a trap door in the wall of his bathroom.

Appearances

 * Scooby-Doo, Where Are You!
 * 116. A Night of Fright is No Delight