ABSTRACT
The maturity or stage of coalification reached by a coal is referred to as its rank. Rank is not measured in percentages or other units, though it is judged by composition particularly the carbon or the oxygen content of the coal. The term is used only in a comparative sense, in such expressions as high rank, medium rank and low rank. It does not imply any superiority or inferiority of quality; low rank, for example, does not mean poor quality.
