Coal originates from dead plant material. Plants photosynthesize by use of light energy to produce glucose they use as a food source. When these plants die, the decay process is sometimes stopped and the energy is kept within the plant debris. This is known as an organic sediment called "peat." This eventually becomes buried and subjected to pressure underground, facilitating the coalification process.
Coal has several "ranks" and is consecutively transformed from the highest to the lowest.
- Lignite: lowest rank, peat transformed into rock, used to fuel generation of electricity
- Sub-butiminous: metamorphosed lignite, loss of oxygen and hydrogen yielding more carbon content
- Butiminous: metamorphosed sub-butiminous coal, most abundant (50% of coal produced in the US), higher carbon content than sub-butiminous
- Anthracite: highest rank, highest carbon content (>87%)
Coal is considered a "nonrenewable resource" because of its difficulty to reproduce. Coal is believed to be abundant in North America, Russia, China, and India to name a few. In terms of contribution to the world's coal supply, China leads with 22% followed by the US (19%), former Soviet Union members (16%), Germany (10%) and Poland (5%).