I have been looking around the forums here for quite a bit to an answer to this question. 

A while ago when I ran out of bituminous coal, I made a run and picked up some more coal. Due to a mistake, I ended up with anthracite. 

At first, I had a tough time using it. I have a buffalo hand crank forge. Needless to say, I had to do a lot of cranking while forging!

What I did notice was that as I was using the coal, it would burn but not be dissolved. I would be left with this, for lack of a better word, "rock". 

While this was not a big deal it did leave me with quite a bit of leftover. After a few weeks of forging I had a bit of "rock" piles. 

Now i was talking to another member about this and we both were curious, The Anthracite burns and is done  what is the "rock" stuff left over? 

With the knowledge on this site, I assume that someone on here uses anthracite and can explain what is going on. 

 

When you burn off the volatiles from coal you are left with coke, in the same way as wood reduces to charcoal. Have you tried burning these 'rocks'? do you have a picture of them?

The anthracite I was given burns down to a lot of clinker.

Are you talking about clinkers? Clinkers are the impurities in coal that dont burn. may glow red but are just being heated by the surrounding coal/coke.  they can resemble volcanic rock, can be hard and make great driveway/ walkway material.   either that or your talking about the coke left over which should still produce heat.

 

Certainly sounds like clinker to me. And yes, it makes for a great walkway! I've been throwing mine on the ground by my forge to slowly build up something resembling solid ground.

They are not clinkers, and as it is anthracite it produces little coke.  Perhaps I did not describe it well enough. The anthracite burned in the forge and it really did not change composition, it stayed in the nut form. Just changed in apperace from glossy black to a dull color. I was able to break the nut up but i had to smash it with a hammer. it chiped like a rock. As a kid we had a coal heater in the house. My job was to clean out the cinders which we used to spread on the driveway.  When i was forging with anthracite it seemed to never break down into smaller peices or be consumed.  I was just wondering if anyone had run into this using Anthracite.

 

I've gotten Some shale (or similar) with my coal before, could be that. pretty much looks like coal at first. I buy "washed" coal now. havnt had any in there since.

So it changed from shiny black to a dull grey? When using full sized "nut" it tends to burn very slowly and goes through that color change. You can break it up in the fire by lightly tapping it and it will burn more effectively. Essentially, the surface area is so small compared to the volume of the piece of coal that it doesn't burn effectively. Using "rice" sized anthracite more or less eliminates this problem.

You can break it up before you put it in the fire or give the big chunky pieces a few light taps with a piece of rod once they have started burning. The latter method nearly eliminates the popping at temperature, but makes fire management more of a pain. I have had success with anthracite, though it took me a while to figure out its quirks.

Jumbojak, I believe you have answered my question.  I would say that it was not possible to break up the Nut sized coal as it was extremely hard, like a rock. I just ended up shoveling it out of the forge when it was done. Another member and I were trying to figure out why this was so.  I also did not like the popping it would constantly do, however, I loved the fact that I could spend all day over the fire and it was so clean. 

 

Banking coal around the fire reduces the popping a LOT. And it's not that difficult to break up. A small tack hammer works very well for that job, if you need to do it. A series of fast, light taps usually takes care of it or you can bank it around the fire and tap it with your rake as heat helps as well.

I have been burning anthracite from Old Town, got for about $16/50#, burns hot, have to start with a good wood fire and use air constantly. this first bunch produces a lot of clinker and would choke off the air supply, I learned that after about two hours to stir the fire up, get the clinker 'unstuck' from itself and let the fire regenerate.

 

Recently have been practicing forge welding in this anthracite fire, if i pay attention to my heat and keep the slag/clinker off the material, my welds will come out, some are less ugly than others

 

Recently I have been using a different brand, Kimble, from Tractor Supply, this seems to have less clinker and costs $6/40# ($15/100) so far this is a win/win.

I've been using the Kimble nut coal from TSC as well. The nut coal as it comes from the bag is much too big, and I usually take a few minutes before I start the fire to break up the larger pieces with a hammer on a block of wood. (I'm thinking I should try the rice coal next, to save myself this step.) As it burns, it doesn't coke the way bituminous coal does; instead, the lumps seem to just keep getting smaller until they burn away entirely.

I've been getting a fair amount of clinker, but I find that if I occasionally kill the air and give the clinker a chance to cool slightly, I can usually hook it out in one or two large pieces.

I appreciate the information. That was the first time I used Anthracite. I have been using Bituminous lately and there is a difference. They both have their pros and cons. I was thinking of getting one of my forges  up and running with an electric blower, I think I might enjoy using Anthracite then as I do not have to work so hard for the air flow. I was constantly cranking.