When the average person considers “types” of coal, they are generally referring to terms that relate to coal rank (lignite, bituminous, etc.) or coal grade (low-sulfur coal, steam coal, met-coal, etc.). Coal type is a specific geologic classification based on the general appearance of coal. Most coals have internal layering, called banding. Coal types, and subsets of types, called lithotypes, are based on the presence or absence of banding, and the brightness or dullness of individual bands. Coal lithotypes are further divided into microscopic microlithotypes, which are composed of different types of microscopic coal components, called macerals. Macerals are to coal what minerals are to rocks (i.e., the building blocks).
There are two basic types of coal, and both can occur in a single coal seam:
References for coal type
- Hutton, A.C., and Hower, J.C., 1999, Cannel coals: Implications for classification and terminology: International Journal of Coal Geology, v. 41, no. 1, p. 157 –188.
- O'Keefe, J.M., Bechtel, A., Christanis, K., Dai, S., DiMichele, W.A., Eble, C.F., Esterle, J.S., Mastalerz, M., Raymond, A.L., Valentim, B.V., Wagner, N.J., Ward, C.R., and Hower, J.C., 2013, On the fundamental difference between coal rank and coal type: International Journal of Coal Geology, v. 118, p. 58 –87.
- Schopf, J.M., 1966, Definitions of peat and coal and of graphite that terminates the coal series (graphocite): Journal of Geology, v. 74, no. 5, p. 584 –592.
- Stach, E., Mackowsky, M.-Th., Teichmüller, M., Taylor, G.H., Chandra, D., and Teichmüller, R., 1982, Stach's textbook of coal petrology : Stuttgart, Germany, Gebrüder Borntraeger, 428 p.
- Stopes, M., 1919, On the four visible ingredients in banded bituminous coal: Proceeding, Royal Society of London, v. B9, p. 470– 487.
Coal can also be defined and classified based on: