Sword of the Godslayer
The man answered, while filling up the wheelbarrow with wood.
"Well, that's what the book said. According to the author, a piece of charcoal is very much like a wizard's stone. He explained that a raw wood like this," he raised a wedge of oak, tried its weight, then placed it back on the wheelbarrow, "is indeed useful for making fire, but the heat it creates is only a quarter of that when you turn the wood into charcoal first.