What are similarities and differences among peat, Iignite, bituminous coal, and anthracite coal?
They are all composed of organic material. They differ in their rank of coalification and related energy content.
All of these compounds are derived from once living carbonaceous plant material that accumulated in bogs and swampy places in the geological past. As they are buried and over long periods of time, peat is transformed into lignite and then with further pressure, into bituminous coal and then anthracite.
Gradually water is squeezed out during this coalification process and the energy content tends to increase.