Coal is not the only rock where fossils are found. The reason coal, oil and methane are considered fossil fuels is because they resulted from dead dinosaurs.
That is the cast in a piece of coal of an ancient fern.
Below is a measure of the diffserent types of coal as well as other fossil fuels. Anthracite is considered clean burning because it was mostly energy with far, far less emissions of sulfur (SO2) and NOx. Yes, Nox. Pronounced "Knocks." Like "Knock, knock" jokes, only they aren't funny. NOx produces "Acid Rain."
Coal releases nitrogen which combines with oxygen in the air and produces NO or Nitrogen monoxide. Coal burning also produces carbon dioxide. 
