Coal was formed from the remains of swamp plants from 300 - 400 million years ago. The dead plants became buried in the swamp. In the absence of oxygen, the plants did not rot, but formed peat. Sediment covered and compressed the peat nearly 80%.
The types of coal are Peat(coal precurser), Lignite(brown coal), Bituminous coal(black coal), Anthracite coal(hard coal), and Coke(coal product).
Peat, Lignite, and Bituminous are sedimentary.
Peat comes from slowly decaying plant matter found in bogs, moors, and muskegs. Acidic and anaerobic conditions prevent complete decay. Lignite sometimes called brown coal is found in Alaska and some Western states consist of low carbon concentration of 30% and low heat value (< 10,000 BTU/lb) and is used in electric power generation. Bituminous coal is the most common form of coal. Anthracite coal results from the metamorphosis of bituminous coal. Its highest carbon content is 85 - 95% and its heat value is 15,000 BTU/lb. Coke is primarily used as a heat source in the steel industry.
