Coal Macerals

Coal is a heterogeneous natural substance consisting of a number of constituents. Microscopically basic coal constituent is maceral which is synonymous to minerals in inorganic rocks. However, there is a difference between mineral and maceral. Minerals are generally inorganic crystalline in nature and has got a definite chemical composition, whereas a maceral is a noncrystalline organic substance and its composition may vary widely. Inorganic substances like mineral matter, shale, clay, and silt are also inherent constituents of coal. These constituents are recognized by the morphology, texture, and gray level or reflectance of macerals. Macerals are classified into three major organic groups, viz., vitrinite/huminite, liptinite/exinite, and inertinite, and one inorganic group, i.e., shale + mineral matter. Association of macerals constitutes microlithotype. These constituents are classified based on mono-, bi-, or tri-assemblage of the constituents.