What is coal?

Coal is a sedimentary deposit composed predominantly of carbon that is readily combustible. Coal is 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 the United States—predominantly in places where prehistoric forests and marshes existed before being buried and compressed over millions of years. Some of the largest coal deposits are located in the Appalachian basin in the eastern U.S., the Illinois basin in the mid-continent region, and throughout numerous basins and coal fields in the western U.S. and Alaska.

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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. The coal in the Powder River Basin is...

Which country has the most coal?

As of January 2020, the United States has the largest recoverable coal reserves with an estimated 252 billion short tons of coal remaining, according to the U.S. Energy Information Administration . Learn more: U.S. Coal Resources and Assessment World Coal Quality Inventory

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...

What is coal used for?

Coal is primarily used as fuel to generate electric power in the United States. In coal-fired power plants, bituminous coal, subbituminous coal, or lignite is burned. The heat produced by the combustion of the coal is used to convert water into high-pressure steam, which drives a turbine, which produces electricity. In 2019, about 23 percent of...
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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: 

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: 

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: 

Attribution: Energy and Minerals
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

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