I would call them and ask if its like that all the way through it might be covered with broken down leaves from the two trees it in between. another thing to ask would be whats the size of most of the pieces of coal you will have a lot of trouble with coal smaller than a computer mouse.
If you want to try bituminous coal you would be far better off buying "new" coal from a dealer or mine, bituminous coal flakes apart if it sits outside for years.