i. The concept type provides a means for classifying standard varieties of coal microscopically on the basis of simple proportions of anthraxylon or anthraxylon and opaque attritus, including their subdivision into banded and non-banded coals.

Ref: IHCP

ii. A type of coal is a variety initially determined by the nature of the ingredient matter, the conditions of deposition, and the extent of operation of the first or biochemical process of coal making.

Ref: IHCP