Is there any known correlation between the HGI of anthracite and its quality (meaning its analyticals as well as its potential burning characteristics)? I believe the lower the HGI value, the harder the coal.
I was also wondering if a simple (poor mans) hardness test of one coal vs. another would be possible, such as putting like size pieces of each back to back (or coal on coal) in a vice and slowly close the jaws, watching which piece crushes first in the process. The one that crushes first (or most) would presumably be the softer of the two coals. Would that indicate a higher fixed carbon and/or lower volatilities or ash content for the one that crushes last (or least) in such a coal on coal vice-crush test?