coal
Coal is made largely of carbon but also features other elements such as hydrogen, oxygen, sulfur and nitrogen. Coal starts off as a plant matter at the bottom of water and is eventually covered and deeply buried by sediments where over time metamorphosis takes place. When peat is altered physically and chemically. This process is called “coalification.” During coalification, peat undergoes several changes as a result of bacterial decay, compaction, heat and time. Peat deposits are varied and contain everything from pristine plant parts, to decayed plants, decayed products, and even charcoal if the peat caught fire during accumulation. Peat deposits form in a waterlogged environment where plant debris accumulated, like peat bogs and peat swamps. The accumulation of plant debris exceeds the rate of bacterial decay of the debris. The bacterial decay rate is reduced because of the available oxygen in organic-rich water is completely used up by the decaying process. For peat to become coal, it must be buried by sediment. Burial compacts the peat and, consequently, much water is squeezed out during the first stages of burial. Continued burial and the addition of heat and time cause the complex hydrocarbon compounds in the peat to break down and alter in a variety of ways. The gaseous alteration products are typically expelled from the deposit and the deposit becomes more and more carbon-rich as the other elements disperse. Lignite coal is the lowest grade of coal and is brownish-black in appearance. This coal forms from organic carbon in plant material like peat. As peat is squeezed at low temperatures it is considered a sedimentary rock, unlike a metamorphic rock that is subjected to greater temperatures and pressures causing profound physical or chemical change. I believe coal starts out as a sedimentary rock and goes through a process called metamorphism, “a change in form” with the addition of heat and pressure. Contact metamorphic rocks are those