Who has actually tested some anthracite coal?

I don't know much about coal at all (I'm learning), but I've got a story to relate that will add some data.
In our guild forge (bgop.org), we burn anthracite in a pot belly stove to heat the place, so we have both anthracite as well as the bituminous coal for the forge. Recently, at the annual shop clean up, some amount of coal on the floor was cleaned up, and thrown into the barrel for the forge. It turns out a great bit of that was the anthracite for the stove but whoever was cleaning up didn't realize the difference. The two types of coals were too mixed up to make separation an option. So recently, we have had to try and use this mix of anthracite and bituminous coal in the forge.
It didn't work well at all. Hard as hell to keep the fire burning and hard to get enough heat out of it to forge with. I don't know how much of this was the particular coal we had, or if it's true in general for trying to use anthracite for forging.
The anthracite we have are fairly large chunks (like 1" size roughly). I'm guessing that larger size really needs a larger sized pot and fire to burn well. So the normal size of the forge pot might simply be too small to burn that larger sized coal. But I suspect it simply doesn't burn as quickly or as hot as normal blacksmith coal, even though the anthracite in general has a higher BTU/ton rating. Maybe a larger sized fire pot, and maybe greater air flow would be required to make it usable? Or maybe it simply doesn't tend to burn as hot no matter what you do making it a very poor choice for forging?
All I know for sure, is that it was a true pain in the ass for us when it got mixed in. Luckily, most of that "mistake" has been burned up now.