Recovered coal fines. The coal company gets some federal money for putting them out. Some are just tightly compressed dust. Some have a binding agent added in.
I guess I'm lucky, there is a man who will sell coal by the pickup truck bed load about 2 miles from my home. There is also about a foot thick seam of coal that is exposed behind my house. I also have picked up half bed fulls from beside the road where a coal truck has to dump some due to being caught overloaded.