Is Coal homogeneous

Answer 1

Coal is only as homogeneous as the original materials from which it is formed.

Many soft coals (lignites) are formed by the burial and compression etc, of forest or shrubland. Thus the coal formed from this will never be homogeneous, and you may find fossilized branches in the material.

Many 'brown coals' give off much gas (methane) and this is a hazard to mining.

Other coals are formed from mossy bogs, which were in a depression, and which continued to sink, with the moss continuing to fill the hollow.

Many of these coals, buried and subject to compression and heat, form coals that are much more homogeneous.

These coals, if buried sufficiently, give off very little gas, and are much darker in colour.

The lowest rank of coal would be peat, which is not changed much from the original plant material. Rank then passes through the lignites and other brown coals, then through the black shiny coals to Anthracite, the highest grade of coal. Graphite may be considered the highest grade of coal, but is not as useful a fuel as the others.