Geochemical and Metamorphic Processes

Once the source beds have been established, the onset of various processes occurs which ultimately results in the formation of coal. The first of these processes is often referred to as diagenesis which takes place under normal conditions of temperature and pressure and also includes the various biochemical processes (Teichmuller and Teichmuller, 1979 Bouska, 1981). There is also the suggestion that as a result of such processes, changes to the coal components may be continuous, insofar as the coal may be changing even in its current beds changes to various coal macerals have been observed under various conditions that are equivalent to the coal-forming, or maturation, conditions (Smith and Cook, 1980). 

The concept of normal temperatures and normal pressures is also a contradiction to the recent work whereby geological time has been simulated by substituting higher temperatures than might have ever been operative in the past. It is also a caution against the use of such data to project the precise chemistry of coal formation. 

The end product of these early processes is (it is assumed) the familiar peat or, often, a soft lignite-type material. 

Once the biochemical stage of coalification is effectively terminated, the changes in the plant debris (by this time it may be approaching peat or lignite in nature) are entirely physical or chemical and are usually determined by the prevailing conditions of temperature and/or pressure. 

Obviously, other factors may also play an important part in determining the ultimate nature of the finished coal. These include the relative proportions of the chemical compounds that form the source material which become part of the coal substance and which are used as food by the microbial organisms. Indeed, the large variation of chemical compounds that can form the source material almost, even at this point, assure the complexity of coal. 

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