Diagenesis coal/peat

The geochemistry of sulfur in coal is largely controlled by sedimentary environments during peat accumulation, as well as by the geologic conditions during diagenesis following peat formation. In low-sulfur coal, peat... 

It seems therefore that stable radicals are formed during diagenesis (possibly by aerial oxidation as well as enzymatic action), but it may be questioned whether it is these radicals that survive metamorphism and are observed in bituminous coals. One of the main chemical consequences of metamorphism is that much of the combined oxygen in peats is eliminated, and one would expect that if the majority of the free radical centers in peats were localized on oxygen atoms, they would mostly be eliminated during metamorphism. 

The minerals in a coal clearly reflect its geochemical environment of deposition and diagenesis rather than the composition of the source rocks. Ferromagnesian minerals such as pyroxenes, amphiboles, and ohvines are very rare in coal feldspars are also uncommon. These minerals are unstable in low-pH peat-swamp environments and are apparently destroyed in the early stages of coalihcation. In contrast, more resistant accessory minerals such as rutile, zircon, and rare-earth phosphates are relatively common in coal. 

Orem W. H. and Hatcher P. G. (1987) Early diagenesis of organic matter in a sawgrass peat from the Everglades, Florida. Int. J. Coal Geol. 8, 33-54. 

The main point of this simple study is that, in cases such as peat/coal and aquatic sapropel/ paper shale accumulations, ultimate geoporphyrin (i.e. DPEP-series) precursors beside chlorophyll-a need to be considered. In order to mold bacteriochl orophyl 1-a into current modified Treib s scheme diagenesis (3-5) only the removal of the 3,4-dihydro and 2-acetyl features are required. That is, an aromatization and reduction/dehydration. 

Altschuler, Z.S., Schnepfe, M.M., Silber, C.C. and Simon, F.O. (1983) Sulfur diagenesis in Everglades peat and origin of pyrite in coal. Science, 221, 221-227. 

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