What is coal?

Coal is a sedimentary rock made predominantly of carbon that can be burned for fuel. Coal is readily combustible, black or brownish-black, and has a composition that, including inherent moisture, consists of more than 50 percent by weight and more than 70 percent by volume of carbonaceous material. It is formed from plant remains that have been compacted, hardened, chemically altered, and metamorphosed by heat and pressure over geologic time.

Coal is found all over the world including our country, predominantly in places where forests and marshes existed prehistorically, before being buried and compressed over millions of years. Some of the largest deposits, though, are located in areas of the Appalachian basin in the eastern U.S., the Illinois basin in the mid-continent region, and throughout the Rocky Mountain basins in the western U.S.

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What is the biggest coal deposit in the United States?

The biggest coal deposit by volume is the Powder River Basin in Wyoming and Montana, which the USGS estimated to have 1.07 trillion short tons of in-place coal resources, 162 billion short tons of recoverable coal resources, and 25 billion short tons of economic coal resources (also called reserves) in 2013.

Which country has the most coal?

The United States has the largest proven coal reserves, with an estimated 260.5 billion short tons of coal in 2008, according to the U.S. Energy Information Administration.

What are the types of coal?

There are four major types (or “ranks”) of coal. Rank refers to steps in a slow, natural process called “coalification,” during which buried plant matter changes into an ever denser, drier, more carbon rich, and harder material. The four ranks are: Anthracite: The highest rank of coal. It is a hard, brittle, and black lustrous coal, often referred...

What is coal used for?

Coal is primarily used as fuel to generate electric power in the United States. The coal is burned and the heat given off is used to convert water into steam, which drives a turbine. In 2012, about 39 percent of all electricity in the United States was generated by coal-fired power plants, according to the U.S. Energy Information Administration...
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Date published: October 23, 2017

Assessments Evolved: USGS Coal Research in the 21st Century

Although often associated with helping fuel the Nation’s growth during the Industrial Revolution, coal is very much part of our space-age present. In 2016, coal-fired power plants provided 30.4 percent of the country’s electricity, and it is an important source of employment in many states.

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Image shows a large black stone with a silver sign in front
July 20, 2016

Cannel Coal

Cannel coal is a type of bituminous coal, which is the second-highest rank of coal (just behind anthracite). This particular sample has a high carbon content with high pollen and spore content as well. Unlike most bituminous coal, Cannel coal can be carved into ornaments. This sample came from the Eastern Interior Coalfield in Kentucky.

Image shows a sample of peacock coal against a rock background
December 31, 2013

Peacock Coal

This sample is of peacock coal. Peacock coal is not a specific class of coal, but rather the name for an effect in which oxidizing materials in the coal create a dazzling array of colors on the surface of the coal. Usually it is short-lived, as the material fully oxidizes away shortly after exposed to air. Read more about our coal research here: 

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Image shows a sample of bituminous coal on a rock backdrop
December 31, 2013

Bituminous Coal

This sample is of bituminous coal, a middle rank coal (between subbituminous and anthracite) formed by additional pressure and heat on lignite. Usually has a high Btu value and may be referred to as "soft coal." Read more about USGS coal research here: 

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Image shows a sample of cannel coal on a rock background
December 31, 2013

Cannel Coal

Cannel coal is a type of bituminous coal that is also sometimes referred to as a type of oil shale. It's name likely came from the word "candle." Cannel coal was once used as a source for kerosene. Read more about our coal research here: 

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Image shows a sample of anthracite coal on a rock backdrop
December 31, 2013

Anthracite Coal

This is anthracite, the highest rank of coal. It is a hard, brittle, and black lustrous coal, often referred to as hard coal, containing a high percentage of fixed carbon and a low percentage of volatile matter. Anthracite is not as commonly mined as other ranks of coal. It played a significant role in Pennsylvania coal during the Industrial Revolution in the United

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Image shows a sample of lignite on a rock background
December 31, 2013

Lignite Coal

A sample of lignite, the lowest rank of coal. It is primarily mined for burning in steam-generation power plants. Read more about our coal research here: https://www.usgs.gov/centers/cersc/science/us-coal-resources-and-reserves-assessment