Coal and natural gas are two of the most important RESOURCES and FUELS used in the world today. Coal is a combustible black or brownish-black sedimentary rock composed mostly of carbon and hydrocarbons, while natural gas is a naturally occurring hydrocarbon gas mixture consisting primarily of methane. Both of these RESOURCES are used to generate electricity, heat homes, and power industrial processes. They are also used as raw materials in the production of various products such as plastics and fertilizers.