Final answer:
Coal is a solid material derived from plants that were buried millions of years ago. It is classified into four types based on carbon content and heat energy. These types include anthracite, bituminous, subbituminous, and lignite.
Step-by-step explanation:
Coal is a complex solid material derived primarily from plants that died and were buried hundreds of millions of years ago and were subsequently subjected to high temperatures and pressures. It is a combustible black or brownish-black sedimentary rock with a high amount of carbon and hydrocarbons.
Coal is classified into four main types, or ranks depending on the types and amounts of carbon present and on the amount of heat energy the coal can produce, including anthracite, bituminous, subbituminous, and lignite.