Wow, very interesting thread! The coal I used last year had a light grayish white color to it. It burned great, although I never compared it to anything since it was my first year. It produced a lot of pieces in the ash, many quarter sized flat and had a resemblance of bone. Many of these pieces were marbled with a brown color. It had many smaller pieces too the same way. I haul my coal with barrels. A barrel of this coal weighed in at about 420 pounds.
Now this year, my dealer is getting his coal from a different supplier. And its only $200 per ton instead of $235 per ton last year for the white ash coal. This coal produces an ash that has a very red hue to it. Kinda looks like the surface of Mars. It mostly burns down to a fine powder and I hardly have any of these pieces that I described with the coal I used last year. Other than the powdery ash, there is some unburnt coal pieces that fall through. Seems more stubborn to shake down. This coal weighs in at about 480 pounds per barrel.
SO you can see the coal I have this year is more dense. Also, it seems to burn longer, hotter, and it seems to not burn down as fast. Just today when I opened the load door to check it, it looked like I just filled it, that was after a 15 hour burn. I shook it down good and only had to add 2 shovels (15 pounds) to bring it back up to where it was. I don't need to push my furnace very hard to keep warm so hopefully I won't have the clinker problem that seems to be associated with red ash coal.
IN the pics below, I put a blue eraser in there for a reference color..
Overall, I think I'm going to prefer this red ash coal over the white ash that I used last year..