What is the chemical composition of "ash" like that left in a fireplace after combustion?Does it contain...?

Question

carbon at all? Clearly it has no usable energy, right? So just what is it?

Answer 1

Its mostly carbon but it contains all the elments that would not combust and go up the flue that were in the tree.  If you went through it I'm sure you'd find Fe, Al, Na, Si, K and lots of other elments found thoughout nature

Its pretty intert at this point, all the volities were burned, its not gonna hurt ya

Answer 2

It's good for gardening! Mix with soil when planting instead of other soil conditioners.