Coal

Coal is a combustible black or brownish-black sedimentary rock composed mostly of carbon and hydrocarbons. It is the most abundant fossil fuel produced in the United States and a nonrenewable resource. Over 90% of the coal used in the United States is used to generate electricity. It's also used as a basic energy source in many industries, including, steel, cement and paper.  
 
Facts

  • One quarter of the world’s coal reserves are found within the United States, and the energy content of the nation’s coal resources exceeds that of all the world’s known recoverable oil.
    Read more at the Department of Energy.
  • Coal is also the workhorse of the nation’s electric power industry, supplying more than half the electricity consumed by Americans.
    Read more at the Department of Energy.
  • Coal is classified into four ranks based on age and heating value, which is graded higher the higher the percentage of fixed carbon content in the coal. The age of the coal also affects how much pollution and emissions are generated when it burns; the older the coal the relatively cleaner it burns. Oldest to youngest:
    • Anthracite - Used primarily for residential and commercial space heating, anthracite is the highest rank of coal. Its hard, brittle, lustrous black texture contains a high percentage of fixed carbon and low percentage of volatile matter. It is often called "hard coal." 
    • Bituminous - Dense coal of black or dark brown color and usually has well-defined bands of contrasting bright and dull material. It is used primarily to generate steam electric power. Substantial quantities are used for power and heat applications in manufacturing as well as to make coke. In active U.S. mining regions, bituminous coal is the most abundant coal.
    • Sub-bituminous - This coal can range in composition from dull, dark brown-to-black in color and soft and crumbly as one quality, to bright, jet black, hard and strong as another quality. Used primarily as fuel for steam-electric power generation, subbituminous coal has properties ranging from the properties of lignite or bituminous coal. 
    • Lignite - This coal's brownish-black color has a high moisture content and is the lowest rank coal. It is often called "brown coal" and is used almost entirely as fuel for steam-electric power generation.  Read more at the Maryland Energy Administration .
    • There is a lot of interest in trying to make "clean" coal by removing the greenhouse gases and other pollutants from coal power generation before they are emitted into the air, through such methods as carbon capture and storage.

Read more at the Maryland Energy Administration