My buddy and I recently made some rice/buckwheat size coal out of four chunks that combined weighed around 1,100 #. We just put them on the asphalt driveway and ran them over a few times with the dozer.
He had found the coal while doing an excavation project (one of the benefits of living in coal country).
There was a little dirt mixed in that I manually sifted out when I loaded the coal into my stove. But the total operation took around 45 minutes so in my view it was worth the effort.
Have fun and be careful!