Peat is a biogenic sedimentary deposit consisting of slightly compacted terrestrial plant debris. Peat is the precursor to coal. Compaction and heating of peat leads to the formation of lignite coal. Further compaction and heating results in sub-bituminous coal, bituminous coal, sub-anthracite coal, and anthracite coal. Peat deposits are geologically quite young and have not undergone any significant burial or diagenesis. Peats form in stagnant, swampy environments. Plant fragments in peats are easily visible to the naked eye.
Peats are brown to dark brown in color, easily broken, and extremely lightweight, especially when dried out. They have relatively low carbon contents compared with coals, but they will burn in a fire. Peat is used as a source of fuel in some parts of the world, but burning peat releases a fair amount of particulate pollutants (it's a dirty fuel).
Peat (4.2 cm across)